Language its Neurophysiology and Disorders

General remarks :Language performance is a highly complex activity. The tongue and lips must make skilled movements and there must be highly coordinated muscular activity involving even areas which are not directly involved in the production of speech. The speech is performed so rapidly that we are not even aware of the process. But speech is more than just a complex motor activity. It is also a complex mental activity which involves the acquisition of the language structures, associating words, objects and concepts and so on. The acquisition, storage and retrieval of language involve the Central Nervous System.

We will present here a sketch essay on the known structure of the Central Nervous System (CNS) and its role in the production and control of speech. We will present also certain important neuropsychological theories proposed as constructs of the process that underlie human behaviour. Then we will identify and describe pathologies of speech from the neurophysiological and linguistic background.

Our knowledge about the structure and functioning of the human nervous system and the brain continues to be scanty in spite of intense research activity in this area. We know now a great deal about the anatomy of the nervous system. We know also about the neuron which is the basis of the nervous system. But nothing in detail is known about how any one particular function is carried on in the nervous system; nor do we have answers to questions such as what happens in our brain when we are involved in language activity, how do we associate a word with an idea, and what is its neurological correspondence, how do we associate a word with an idea acquired long ago, what is the corresponding neural activity for the thought which occurs before we start speaking, what is the precise nature of the storage and retrieval system that must underlie language and all human behaviour.

The nervous system consists of billions of neurons which are interconnected. These neurons are the basis of the nervous system. The neuron is a living nerve cell. It is a small mass of protoplasm covered by a semi-permeable membrane. This membrane allows the materials essential for maintaining the cell's life to enter and the waste products to go out. The neurons have some features common to all of them. These include cell body, cell nucleus, the axon or nerve fibre, terminal arbor, dendrites and synapses. (See Fig-1).

The cell body contains the cell nucleus. The axon is a fine filament which extends from the cell body and which can be even several feet long, as in the case of the axon from the spinal column to the muscles which control the movement of the toes. The axon has several side branches and these side branches terminate as the terminal arbor in a fine network of filaments. Dendrites are extensions that sprout from the cell body of a different neuron. Synapses are the junctions at which connections between neurons are made. The synaptic junctions are very important for the activity in one nerve cell to excite the neighbouring cell.

Receptor cells are those cells which receive sensory information from their environment. These help in coding the information thus received into electrochemical pulses which are responded to by the effector cells. The fine surface membrane which covers the neuron maintains a difference in chemical constitution between the neuron's interior and exterior.

The interior of the axon contains a concentration of positively charged potassium ions. The cellular fluid through which the axon runs contains positively charged sodium ions. Negatively charged chlorine ions are present in both fluids. The neuron is stimulated strongly and this stimulation leads to a quick exchange of ions between the inside and outside of the surface membrane. A pulse of electrical activity passes along the axon. But energy is not transmitted from one point to another over the axon. It is only the local electrical activity that moves along the axon.

A neuron must be sufficiently stimulated for the impulse to be sent along the fibre. The stimulus thus sent must be increased to the neuron's threshold level. When the stimulus is sufficiently greater than the level of excitation the neuron sends a pulse along its axon. The shape and amplitude can be relatively independent of the intensity of the stimulus. We notice a refractory period, very minute indeed, but this refractory period is sufficient enough to avoid the production of a new pulse, regardless of how intense the stimulation is. This is an absolute refractory period. There is yet another refractory period slightly longer in which the neuron's threshold level will be higher than the normal level. Neurologists relate these intervals to the time necessary for the displaced ions to move back to where they were before the pulse occurred. Notice that this time gap is also necessary for the completion of an utterance. Note also that we have the phenomena in which the overlapping of utterances takes place.

The production of pulses by the neuron depends upon the intensity of the stimulus. There is a limit, however, on the number of pulses which a neuron can produce each second because of the refractory period. When the nerve fibre reaches its maximum rate, increase in stimulus activity can have no effect. Several fibres are fired even for hundred pulses per second. The diameter of the axon decides the velocity at which a pulse travels along a nerve fibre.

The large nerve fibres of human beings have a layer called the myelin sheath. (See Fig.2). This sheath is a fatty substance and is an electrical insulator. This sheath has periodic nodes at which very short lengths of the axon membrane are exposed. The pulses seem to proceed with greater speed in such nodded fibres. There seems to be a jump from one node to the other. Though the process and the organization are not yet fully understood, the noded fibres seem to be a leap forward in the wiring structure of the nervous system. This is so because the lower forms of life do not have such noded fibres.

We do not have myelin sheaths for dendrites and nerve endings. Neurologists find that we transfer activity from one nerve to the other with the help of these. But again the process is yet to be fully understood. They suggest chemical means for the transmission process across synapses. The synapses can have either excitatory or inhibitory function. In the first a pulse reaching a nerve end makes the succeeding neuron fire. In the second a pulse reaching a nerve end prevents the succeeding neuron from firing. It is the combined effect of the stimuli that finally determine the response.

The central and peripheral systems : Their roles in information processing :

The nervous system may be divided into central and peripheral subsystems. The brain and the spinal cord make the central nervous system. The peripheral system consists of the nerve fibres that connect all the parts of the body with the central nervous system. The fibres of the peripheral nervous system may be either sensory or motor. The sensory fibres transmit impulses initiated by external stimuli to the central nervous system generally. The motor fibres of peripheral nerves conduct the nerve pulses to the parts of the body to cause appropriate muscular movements. There are also other fibres of the peripheral system. These fibres go to organs of the body, such as glands and control the activity of these organs.

The central nervous system is responsible for the coordination and direction of most human behaviour. The central nervous system sorts out the information brought by the peripheral nerves, interprets the information and inititates appropriate action. The central nervous system can also initiate its own action without external stimuli.

The CNS seems to be organized on some hierarchical lines. The spinal cord is concerned with the interpretation of elementary information and initiation of elementary activities such as automatic reflex responses. The brain may be considered as the high level in this hierarchy (See Fi.3). The medulla oblongata which lies at the upper end of the spinal cord, controls the reflex mechanisms of the respiratory, circulatory and digestive systems. The cerebellum receives information about body position and movement, and muscles and their movement. The central hemispheres have many deep convolutions. The control many lower functions as well as memory, consciousness and voluntary activities. The human brain's hemispheres have a great complexity that has not been found in the brains of animals. The folded surface of the hemispheres have concentrations of neuron. These concentrations are known as the cerebral cortex.

As stated earlier, the neural processes involved in the thought prior to speech, speech production itself, retrieval of speech and so on are poorly understood even today, though we have now a variety of techniques to obtain information and conduct research in this area. Anatomy of the nervous system is largely known through postmortem dissections. This has enabled us to trace the origins and ends of nerve fibres, to have a good description of the kinds of synapses and the neurons.

Scientists have made observations of the nervous functions using live animals. The electrodes inserted in different parts of the auditory pathway observe nerve pulses which result from the acoustic stimulation. Again the electrodes are used to map the areas of the brain essential for certain functions like hearing, vision, or motor activity. Certain areas of the brain have been removed and the resultant activity or lack of it studied. Likewise certain nerves may be cut and the resultant communication conditions studied. This enables us to know about the functions of various localized areas of the nervous system. The external electrodes are used to observe electrical activity. However, major surgery

1. Cerebral Hemisphere	4. Thalamus
2. Cerebral Cortex	5. Medulla oblongata
3. Cerebellum	6. Spinal Cord

is necessary to observe electrical activity in localized areas and this involves danger to the subject. Still direct experiments have been conducted on the brain, as a last resort only on cases whose maladies are severe. And on the basis of such direct experiments we come to know of the essentiality of certain localized areas of the cerebral cortex for the production of speech and comprehension. This indicates that large areas of the brain may be removed without impairing speech production and comprehension.

A speech production originates from a high level in the central nervous system; whereas the hearing process begins in the inner ear. The inner ear receives the signals and these signals are conducted to the sensory centers of the cerebral cortex. While such signals are transmitted, some information processing may take place at the synapses. The information is carried on to the central nervous system. Further there is a complete and complicated feedback loop by which control is exercised over the peripheral organs. We do not however know in any detail the what, how and why of the information processing procedures.

It is still a mystery as to how the acoustic signals are perceived by the ear and then transmitted to the central nervous system. We do not know how our ears determine the loudness, how they analyze the complex sounds into component tones and so on. The current view places an emphasis on the inner ear's capacity to analyze the frequencies of the sound waves.

The hypothalamus, a phylogentically very old part of the brain, is considered to be the motivational center of the brain. This seems to control several behaviours and physiological functions, such as sham rage, regulation of body temperature. The reticular activiating (RAS) is located above the spinal cord and below the thalamus and hypothalamus. This system seems to be involved in sleeping, wakefulness and attention. The RAS is stimulated by the sensory information and it relays this new information or the presence of stimulation to the cortex. This is sent in the form of attention calls which enable the cortex to get ready to process the specific information through specific input channel to the cortex. Attention thus seems to be controlled by the RAS, the destruction of which can make the animal to tune off completely.

Neurophysiologists suggest that habituation takes place as soon as novelty of stimulation is lost. Habituatory control perhaps is not the function of higher brain centers which may concentrate on more novel and significant information. The distinction between habituatory and non-habituatory information and the relative importance and novelty of the information may be made either at the periphery or in the central analyses. Knowledge on this count is scanty once again.

We have two kinds of views about the neural basis for the retention of learned behaviour in the dynamic view, the learning situation leads to a continuing electrical activity in appropriate neural circuits. The memory is related to the persistence of the continuing electrical activity in the circuits. In the structural view the learning situation leads to some rather long lasting physical change in the nervous system. This lasting of the physical change is not dependent upon the original circuits which brought in the change. Experiments have shown that even when the electrical activity is reduced or completely eroded, the learning continues to be retained. As regards the second view, information is scanty and controversial either to confirm or to reject it. Neurological evidence suggests that the ribonucleic acid (RNA) is a very strong contender for being the memory molecule.

Neurologists attempt to identify the biochemistry of the brain, seeking answers for the difference in the learning capabilities of individuals. They try to identify the chemicals, and their relative spread in the different areas of the brain. They try to measure the amount of chemicals in neural cells in specific brain structures and identify the changes they undergo in specific activities undertaken by the subject. One may manipulate the rearing and learning experiences of animals with a common background and identify how their brain chemistry has been changed in the light of experience gained. Further, one may find out how the behaviour of individuals with different distributions of chemicals vary from each other.

In the previous sections we presented some information about the network and the functions of nerves and the central and peripheral systems with their roles in information processing. Before we take up the neurological models of behaviour, we would like to draw the attention of our readers to two approaches to speech perception, viz., the motor theory of speech perception and the auditory theory of speech perception.

The current research on the role of motor movements in perception, especially of speech perception, indicates that a child perceives sound sequences in terms of his own motor reactions. This motor theory of perception, however, does not deny the importance of the acoustic events, but gives priority to the motor kinesthetic feedback loops in the comprehension-use of language. For the motor theory of perception the proprioceptive impulses are very important. They have their origin in stretch or tension, receptors in muscles, tendons, joints, and in the vestibular apparatus of the ear. 'The resulting appreiciation of position, movement, balance and change in the equilibrium is called proprioception or kinesthesis' (Berry, 1969). Proprioception is carried on in sensori-motor loops with bi-directional tracts. These sensori-motor loops are found to be used in comprehension -- use of language. A.M. Lieberman, the chief proponent of the theory, asserts that the perception of speech sounds is somehow more closely related to the articulation than to the acoustic stimulus. Speech is perceived by the articulatory movements and their sensory effects mediate between the acoustic stimulus and its perception. The articulatory movements that a listener makes in reproducing the acoustic patterns help in determining the cues for perception of words. Linguists like Twaddell (Twaddell 1952) also are of the opinion that listeners classify sound sequences on the basis of motor articulation rather than acoustic properties. Further some psychologists like Sherry (Cherry 1957) suggest that if there is an order in acoustic and articulatory events, we perceive the sound sequence only after the neuromuscular patterns of articulation have been mediated. (For details of this approach, one may like to read A.M. Lieberman's articles particularly Lieberman, et al 1963; and Lieberman, 1957).

The studies in the auditory perception of speech concentrate on a person's ability in hearing for speech. In these studies, the attributes of tone, namely, fundamental frequency, amplitude and duration form the basis of analysis and are found embedded in the discrimination cues to phonemic sequences of speech. The auditory perception researchers study also how the different parts of the ear and other systems such as reticular, thalamus and cortex are involved in the auditory perception. These studies deal mainly with the temporal management of information from the input. They aim at explaining how a person's nervous system learns to comprehend and make use of auditory information. Such studies include several information, namely, analysis of the rapidly successive bits of information that crowd the auditory mechanism at the initial stage, initial patterning of the information through activating and feedback processes, linking up these patterns with other wave patterns from modalities and modification of wave patterns effected partly by earlier patterns activated in cortical and subcortical areas. Auditory perception of speech depends also upon memory, that is, the retained auditory patterns in the nervous system. The physiological limits set by the auditory apparatus may also be studied in the auditory perception of speech.

The studies of auditory perception of speech, thus, include both the physical aspects of sound and the physiological aspects/apparatus for audition. In these studies, time as a measure is considered to be a very important factor in all the neural events including frequency variations, duration of input signals, periodicity into elements, identification and match of elements, and in the production of speech patterns (Berry, 1969). The auditory perception may be imagined to be taking place in several phases. Berry (1969) presents three phases in auditory perception of speech, while agreeing at the same time that such identification and segmentation of auditory processes of perception are merely a kind of abstraction for the matching of specific neural activity with the temporal phase. In the first phase activation of neurons takes place and this requires a chemical mediator which is responsible for the sensitivity of end organs. Further the change in the end organs should be transformed into a form of energy capable of discharging the nerve terminals. In the second phase, the wave pattern makes connections with various parts of the hearing apparatus. While these connections are being made, modification and discrimination of the auditory patterns continue. At this stage information from other modalities, particularly from the reticular system, is available for organizing and focusing the perceptive field of audition. In the third phase, certain neural events occur in order to improve the quality of the perceptual processes of audition. All the systems that are relevant for perception in general pool their resources in arriving at a comprehensive auditory perception of speech and other events. At this phase short-term memory (use of retained auditory patterns from earlier inputs) is utilized. Analysis by synthesis of various number and kinds of information is the highlight of the auditory perception process in the third phase. In linguistic terms, ordering and sequencing of syllables, words, phrases and sentences are achieved in this phase. For detailed information in relation to aspects of auditory perception of speech, the readers may refer to Fay (1966), Lieberman (1967), Rosenblith (1961) and Granit (1962).

In every society we have a belief in one form or the other that man's intelligence is a gift given to him by the Almighty. There is also a belief in every society linking brain and intelligence. The existence of such a belief can be found in their language inn which the intelligence is referred to as emanating from the brain. Many societies posit entities called mind, brain and others which are supposed to control human behaviour in some sense or the other. Clinical neurologists, neuropsychologists and neurophysiologists-several of them - are and have been involved in intense research work to identify the exact cerebral localization for the various mental and physical functions. In fact the clinical neurology and neuro-physiology are dominated by research activities with the identification of exact cerebral localization as the main focus. Researchers demanding 'exactitude' assume that they can find a correlation, perhaps one to one correspondence, between the part or structure of any size of the brain and specific kinds of behaviour or functions. For every action and for every function there must be a center, a nerve or something else in the brain and in finding such correlations depends our ability to characterize and explain human behaviour. The above assumption is a historical product and is a direct reflection and extension, in general, of the reflex theories. Coupled with such a concept of cerebral localizations is the attempt on the part of the researchers to seek their models in the machines and mechanisms about which they have an explicit knowledge. Usually a communication model is constructed and the characteristics of these models are assumed to be the underlying neural processes etc., on grounds such as communication is not possible without these characteristics and so on. Thus we have theories based on hydraulic systems, telephone, radio and others. Such an approach may clarify the issues and sharpen the focus. At the same tie it can lead to a narrow view which leads to comparisons, and deductions based on materials which may not have direct relevance. We must rather study the brain and the behaviour to find out how the brain works instead of making comparisons. Similarities in such comparisons may be the product of an oversimplification of the problem of behaviour.

Earlier we have presented certain anatomical descriptions of the parts of the brain, neurophysiological processes and indicated even certain localizations of functions in the brain parts. We will present below three approaches which are in some complementary to each other in accounting for the neuropsychological organization of human behaviour including language.

Our behaviour is a product of our nervous system. This fact has been recognized by psychologists. Many psychologists have used neurophysiological constructs even as the basis of their theories. Even linguists are no exception to this. However, there is and has been a very strong tendency to base the explanations mainly on the observable phenomena. As a result the physiological constructs have been avoided in several influential psychological theories.

Bloomfield, the most influential among the American structural linguists, opposed the mentalistic interpretation of language and took a behaviouristic view. Linguists were in the process of establishing their field as a separate entity and they succeeded to a large extent in their effort. In this effort and process, the emphasis has been to avoid the so called psychologizing and neurophysiological assumptions and implications, even though some makers of modern linguists resorted to neurophysiological interpretations of the language phenomenon and its underlying mechanisms.

The field of psychology also has been characterized in the past by the use of certain constructs which cannot be directly observed. The behaviourists emphasized the need to base their constructs and explanations on the directly observable phenomena. Coupled with this movement was the swing towards the separation and establishment of psychology as an independent field of activity on its own merits.

Though such a demarcation of the fields, and establishment of independent constructs and techniques are essential for any field to grow and to contribute in a precise manner to the general body of knowledge, excessive independence can lead to disastrous results. This is especially so with regard to the relationship between psychology and neurophysiology. This is true also for the relationship between psychology, linguistics and neurophysiology.

Hebb (1949) presents a theory of behaviour, seeking a common ground with the anatomist, physiologist and neurologist, showing them how the psychological theory is related to their problems. He finds that one is forced to oversimplify when he deals with behaviour, because of the scanty knowledge we have about the underlying mechanisms. This leads one to a kind of concealed mysticism, even when one takes a formalistic view.

Though psychologists take for granted that the behaviour and neural functions are perfectly correlated and that the problem of understanding behaviour is the problem of understanding the total action of the nervous system and vice versa, Hebb finds, to his regret, that there is a tendency in psychology to stop using physiological hypothesis. He also finds that many physiologists take the same position with regard to psychology. One is on a formal and certain ground when he studies the electrical activity of a well-defined tract in the brain. However, a question arises as to whether such specific and particular studies alone can lead to a physiology of the human brain. The parts and their properties may be discovered in isolation, but the parts may have properties not discernible in isolation. Perhaps it is necessary to study the brain as a whole, in addition to a study of the specifics and parts of the brain, to have a clear and realistic picture of the functioning of the human brain. Hence Hebb calls for learning about what the parts of the brain do , which belong basically to the physiologist's field and for relating the human behaviour as far as possible to this knowledge, which is basically the psychologist's field. He calls for seeing what further information can be had about how the total brain works from the discrepancy between actual behaviour and the behaviour which would be predicted from the addition of what is known about the action of the various parts of the human brain.

The problem we face in accounting for human behaviour has two facets. From the psychological view it is a problem of thought. Here we have a process which is not fully controlled by environmental stimulation and yet it goes along with the environmental stimulation. From the physiological point of view it is a problem of the transmission of excitation from sensory to motor cortex. Transmission can be a very complex process involving time-lag between sensory stimulation and the final motor response. Hebb considers that both psychology and neurophysiology are not in a position to handle thought and its corresponding neurophysiological mechanism adequately. One is not in a position to describe behaviour simply as an interaction directly between sensory and motor processes. Something intervenes and this something we call thinking. This thinking must be due to the operation of central processes. Though one is able to identify the pathways to cortex and the pathways from cortex and also about the structures that link the two, the complexity of the links is not yet fully understood. As a result one does not know anything about what goes on between the arrival of an excitation and its later departure from the motor area of the cortex. Two types of formula have been proposed to account for the processes. The first one may be called a switch board theory and the second one may be called a field theory. In the first type the cells in the sensory system acquire connections with cells in the motor system. The cortex functions as a telephone exchange. In the second theory the conception of field is utilized. The cortex is made up of cells and the sensory control of motor centers depends upon the distribution of the sensory-excitation, ratios of excitation and not on the locus or the action of any particular cell. Connections do not control learning. However, Hebb finds that both these two theories do not account for the delay between stimulation and response which is characteristic of thought. Intra cerebral events must be a prolonged one is such a case. But this has not been explained or provided for.

Hebb presents a speculative physiological theory of behaviour with a synthesis of psychological information. This presents a temporally organized intra cerebral process with the psychological facts of perception, learning, expectancy, attention and soon. He suggests that a frequently repeated stimulation leads to the slow development of a cell assembly. This is a diffuse structure of cells in the cortex and diencephalons and possibly in the basal ganglia of the cerebrum. This can act as a closed system delivering facilitation to other such systems and usually having a specific motor facilitation. The series of such events makes a phase sequence and this phase sequence is the thought process.

Each assembly action can be aroused by a preceding assembly. It can be aroused also by a sensory event. The central facilitation issuing from one of these activities and impinging on the next is the prototype of attention. The adult waking behaviour is the result of the cortical organization of the slow development of a cell assembly. There is an alternate intrinsic organization. This occurs in sleep and in infancy and consists of hypersynchrony in the firing of cortical cells. There is also disorganization as the assembly depends completely on a fine and delicate timing which might be disturbed by metabolic changes and sensory events which are not in accordance with the pre-existent central process. Transitory type of such disturbance is called emotional disturbance. A chronic disturbance is neurosis or psychosis.

Hebb's theory, as he himself calls it, is a form of connections, one of the switchboard variety. The connections are not direct connections to and from the cortex. The connections are there to establish autonomous central activities and these autonomous central activities form the basis for further learning. Further no nerve cell or pathway is essential to any habit or perception.

A.R. Luria of Soviet Union is a great neuropsychologist of all times. His contribution to an understanding of the organization and disorganization of human behaviour is of vital importance for many reasons. His experiments were conducted mainly on human beings, using that medium, namely, language which defines man as man. Luria identified and established a method for neuropsychology to probe and penetrate the underlying mechanisms not manifest in overt behaviour.

Luria argues that the complex mechanisms of organization and disorganization of human behaviour cannot be explained as a simple play of neurophysiological processes. The causes of the affective processes should not be sought in the peripheral apparatus, but in the central. No phenomena of elementary neurodynamics can explain the configurations of integrated behaviour specific for the human beings as social subjects. Perhaps even the elementary neurodynamics may be comprehended only through an analysis of the culturally created psychological functions which include the involved behaviour of work, speech and complex indirect operations.

Luria does not attempt to deduce the laws of higher activity from simple neuro dynamical processes. Neither the laws of dynamics of tendency nor the conditions of reflex connections can throw light on the most complicated forms of human behaviour. Only a careful description of the specific systems of behaviour produced in the process of socio-historical development alone will help us in comprehending the higher neurodynamics.

Luria attacks the tendency to introduce naïve concepts and analogies with artificial things to explain the nervous system. The telephone system was considered the basic theory of nervous activity. Related to this is the concept of the structure of neuropsychology, which posits a series of separate self-sufficient mechanisms. These mechanisms were assumed to have been arranged with the help of the connecting excitations and inhibitions.

In the above view, the whole nervous apparatus is assumed to consist of separate neurons and the brain is assumed to be nothing more than a centralization of these neurons and their conduits which connect the neurons. Accepting this assumption means that the laws of behaviour must be found in those laws which hold for the individual neurons. The behaviour has to be understood merely as a preservation of equilibrium between the separate apparatus of the nervous system. The pathological conditions which one notices must be deduced as a destruction of this equilibrium. This kind of analogy leads to naïve postulations. This makes one to postulate that the elementary processes of excitation and inhibition are basic, founding every nerve cell and carried throughout the whole organism. This also leads one to believe that at a given moment only certain cells of the nervous system are in a state of excitation and others in a state of inertness. Other cells are in an inhibitory condition.

Luria suggests that the process of excitation and inhibition are elementary processes and this occurs in the isolated nerve preparation. Luria asks whether we can express all the forms of organization or disorganization of human behaviour in terms of elementary inhibition and excitation. He finds that this conception does not extend adequately to the whole phenomena. The behaviour cannot be explained as an equilibrium of the separate systems. The disease of any of the mechanisms causes general changes which can be understood only from a most complicated functional, reciprocity of the internal behaviour. The conceptions which one needs for an understanding of the characteristic mechanisms of complicated human behaviour requires that we take into account the whole organization of behaviour, with its structure and dynamics. The organization is sought in a functional correlation of the systems because these systems are not combined in an accidental way but as very definite parts into an integrated functional structure. The parts are functionally equal. Certain systems are meant for governing and regulating while others for supporting and exacting one for another function.

Luria finds that the organization and disorganization of human behaviour, conditions, laws and formulations are the most important problems of psycho-biology. There are some general laws operative in the organization of behaviour. These general laws depend upon the inclination of some special vital forces. The organization we find in adult human behaviour is the product of a fairly complicated and long development. This development precedes in such a way that it dominates the primitive laws and not in the way that it becomes the simple representations in new stages. By taking a developmental view we can arrive at an understanding of the activity of the human personality. The development will include the new regulating systems intended to overcome the primitive forms of behaviour and transfer them to a new and more systematized organization. In this development the question of age does not play the leading role. The primitive forms of organization of behaviour is characterized by the sub-cortical activity. This activity is transferred into the process of the highest development. There is a conflict between the development of newly regulated systems and the primitive sub-cortical activity. The conflict creates all the new forms of organization. The higher cortical mechanism plays an active role in the formation of the new organization. Because of this participation the higher cortical mechanism is included in the regulating systems.

The development of a child involves several processes. First there is a general development of regulations and this begins with the primitive aspects of instinctive capabilities. With the development of higher psychological mechanisms the most complicated forms of control of behaviour is achieved. Such an achievement begins with the complicated organic mechanism and with the higher cultural systems conditioning new forms of organization.

There are two general groups of approaches for the study of the motor functions of the human being. In the first group scholars study the development of motor movement co-ordination, motor formulae and their destruction caused by certain diseases of the nervous system. This study concentrates on the motor function as a physiological process. This can conceal symptoms underlying the disturbance. In the second group the motor activity of the human being is only a means to study the complicated psychological and physiological processes. The structure of the movement is studied as a reflection of certain changes concealed from immediate observation. For the scholars who pursue this type of research the motor activity is significant in so far as this is connected with the psychological changes. Such an approach makes the investigation more complicated and yet infinitely more significant than the previous one. The main problem is to differentiate the motor changes which are the product of the psychological influence from those resulting from the organic peculiarities. Luria's research is more closely allied with the second group. He is only very slightly interested in the motor activities of the subject per se.

Luria suggests that we study voluntary movements in the analysis of behaviour. The voluntary movements are not less regular, not less suitable than the reflexes. He argues in favour of the combination of the central and the motor activities in one functional system. If we combine we can record that the central change is necessarily reflected in the motor system. What we have here is a united whole. The central part is concealed from direct study and yet the motor functions can be objectively registered. This method of the basic combination of the central and motor activities is called the combined motor method. Luria steered his researches toward an understanding of the neuro-psychological processes through the combined method. The subject is asked to reply to a word given him by the first thought which enters his mind. While doing so he is asked to press the finger of the right hand of the receiver of an apparatus lying in front of him. Such a process stimulates in the subject two systems of activity. These systems are connected with each other so closely that they are set into motion by two simultaneously occurrence of the activities of one and the same process. When we ask a subject to answer a given word by another one, his central process is excited in a very complicated manner, and this is very close to the speech system. When we analyze the result psychologically we can in some cases find its associative process, in some cases its primitive fate and in others 'its reintegration with the origin of the whole image of the details contained in the word, or the production of some other details entering together with what is represented in the word-stimulus into one and the same formation'. In this process we evoke definite and a complicated neuro-dynamic process which cannot be observed immediately and which leads after a certain period to the speech response. The language response is connected to the motor reaction of the hand and uniting those two into a single process, Luria finds that we can estimate 'the actual changes in this obscured process as necessarily reflected in a clearly defined process and we see that the differences in the neurodynamic structure of the central process are reflected in the evident differences of structure in the motor curve'. Luria suggests that every short fluctuation and every tendency to a speech response, and, even more so, every marked affective disorganized character of the central process does not remain without influence on the structure of the compounded motor reaction ; and analyzing it, we have at hand a very objective means for drawing conclusions concerning the structure of the internal neurodynamic process'.

The psychologists and neurophysiologists who are interested in identifying the hidden processes between movement of stimulation and the movement of clear response have to surmount many obstacles. Failure in characterizing the underlying mechanisms is due in no small measure to this almost insurmountable obstacle. We have to find out whether the evident response is indeed the result of the undisturbed and uninterrupted process or the process is connected with the struggle of the direct tendencies. There can be internal suppressions. Even an honest subject can inadvertently or because of his socio-cultural inhibition may suppress his original response and give another one in its place. Luria is aware of these difficulties and suggests that the combined method can be so manipulated that we can objectively study only the central process. In a number of experiments the subjects are sought to answer with the first word they thought of. In these experiments they are asked to first give the answer and then press the button.

What we have in behaviour is a union of internal processes and its resultant manifestation. In the combined method what we get in essence is an active union which gives us a unified acting structure. The unified acting structure consists of both the obscure and externally observed symptoms. The changes initiated in one side is reflected inevitably in the other side. An analysis of this active union enables us to study the character of the highest psychological processes.

Luria, thus, is a psychologist, a neuropsychologist using mainly the linguistic utterances as basic items/tools for the analysis of underlying mechanisms. He occupies a unique position among the psychologists and others, because of his use of linguistic items and lucid exposition of underlying mechanisms. In addition to using linguistic items as tools of his analysis, Luria has conducted several experiments to identify the underlying mechanisms of language performance. We give below an experiment he made to elucidate the conflict of the language.

We find that various languages use very different words for one and the same set of contents. A person speaking in a language creates a definite setting in that language which loses its forms when transferred to another language. But the expressed contents remain completely untouched as far as the motor innervations are concerned. Luria in this experiment aims at brings into collision such language settings, evoking a conflict of two very complicated structural systems. He wants to investigate the neurodynamics of the conflicts that may result in a person in such a transfer.

Subjects who know the languages equally well are given words from both these languages and are asked to answer by the first word they thought of in every case. But the answer must be given in the language of the given stimulus in every case. Thus the experiment includes the conditions of the conflict. The conflict, however, is not connected with the content of the word. There are two parallel series of the experiment. This is to ensure that the relations we obtain are not connected with the ignorance of the foreign language but with the factor of the sudden change of the setting. In the first series five foreign words are scattered among twenty five Russian ones. In the second series, five Russian words are scattered among twenty five foreign words. A basic setting is created when the first eleven words of each series are from the basic language of the series. The stimuli words themselves are of equal difficulty. The results indicate that one problem is quickly transferred to another language setting, after the setting to that language is created. It is found that crucial reactions occur with a distinct slowing and considerable disturbance in the accompanying motor system. Associations do not create the disturbance as the subjects know both the languages equally well. The disturbance is due to the position of the critical words in the series. This is revealed in the second series which has only five Russian words scattered among the twenty five foreign words. The critical Russian words call out more inhibited reaction than even the foreign critical words in the Russian series. This is because we have two processes - a transfer to a new setting and a removal of the former setting. We meet with disturbance in the accompanying motor activity in cases connected in one way or another with the conflict of the settings.

The sudden appearance of the new language setting produces a shock which may disturb the receptory activity or cause a conflict in the motor system. The receptory failure is due to the sudden change of setting. The reaction to word depends upon the context in which the word is used. It is found that when the context is altered, perception can be difficult, the word inaudible or it changes its sounds and so on. In the second case, a setting is created to react to definite language. This setting is not removed during a sudden transfer and continues, when the transfer collides with this tendency to continue. A conflict in the linguistic motor system is brought out. The subject begins to give the equivalent in the basic language instead of working himself to think and give another word. Such a tendency can even be extended to non-critical words in the series. These processes indicate the conflict the subject is undergoing. The conflict in the motor activity is clearly shown in the graphic curves. The conflict causes a shock of the higher speech processes in the subject. This is accompanied by a breaking of the functional barrier and the emancipation of the motor area from the connected organized process. The inhibition of speech reaction we find usually in such shocks and transfers is found to be due to the direct transfer of the excitation to the motor sphere. Further the conflict caused by the critical stimuli leaves traces which continue for some time and gets extinguished only gradually, influencing all the while the reactions to other stimuli.

Luria, like his late colleague Vygotsky, recognizes that speech can be used for auto-stimulation and organization of behaviour. Speech is the means of regulating and organizing the external world. It is an agent for organizing the behaviour. It is an agent for planning further actions; it enables the human to avoid subordination by direct optical means. Organizing the behaviour begins with speech auto-commands and ends with the complex forms of judgement. Luria finds that the mechanisms of the substitution of the primitive process by cultural signals is the most important factor in the control of human behaviour.

Finally, Luria is skeptical about the attempts which localize the intricate psychological process in parts of the brain and the nervous system. It is easier to think in terms of things than in terms of process and this is perhaps the reason for continuing attempts to localize the psychological processes. It must be assumed that the acquisition of speech, the use of instruments and the transition of the new cultural forms of organization of the individual behaviour, all achieved in social setting, will also change the structure of the psychophysiological processes. These changes, the functional changes, are much more important, for in several cases. Luria claims, the use of these compensates for serious defects in the morphological structure of the nervous apparatus. There may be a definite organization of the cerebral apparatus underlying complex psychological phenomena, but there need be no specific morphological new formulations for every peculiarity. 'Cultural behaviour does not require a new brain morphology, and the brain of a savage may be morphologically identical with that of a member of Academy of Sciences.'

Lashley's contributions are very significant of an understanding of the organization and control of behaviour. Lashley did not use linguistic utterances as his major tool for the analysis of the underlying mechanisms of human behaviour. He relied upon surgery to demonstrate the untenability of the localization concept. In Lashley's words : 'In experiments extending over the past thirty years I have been trying to trace conditioned reflex paths through the brain or to find the locus of specific memory traces. The results for different types of learning have been inconsistent and often mutually contradictory in spite of confirmation by repeated tests' (Lashley 1960). Both Lashley and Luria arrived at some similar conclusions and findings through the use of different approaches, methods and tools.

Lashley has chosen rats and monkeys as his subjects. In a few cases chimpanzees were also his subjects. He followed two lines of approach. In the first one which is a behavioural type the analysis of the excitations was done. These excitations are actually associated wit reactions in learning and are effective in the elicitation of the learned reactions. Lashley analyzed the associated reactions also. This approach defined the patterns of nervous activity at the receptor and effector levels. The second approach is by surgical destruction of parts of the brain. Lashley trained animals in wide ranging tasks from direct sensory motor associations to the solution of difficult problems. Portions of the brain and associated links were cut or removed. The resultant effect of these surgical operations were measured. When the experiments were over the brain parts were sectioned and the extent of damage reconstructed from serial sections.

In an experiment monkeys were trained to open various latch boxes. After this training their motor areas were removed resulting in a temporary paralysis. Yet, after eight to twelve weeks the animals became capable of opening the boxes. The monkeys did not have access to the training boxes. When sufficiently recovered they did not exhibit even exploratory movements. Hence learning must be considered as the specific localization of the whole of cerebellum.

As regards the role of cortex and the connections to it, Lashley's experiments showed that neither the motor cortex nor the connections are indispensable for the transmission of the conditioned reflex pattern. Lashley trained rats on the maze and then made knife cuts through the cortex and underlying fibres. This disconnected or cut through different functional areas. After recovery the animals did not show any significant loss of the learned behaviour. The general assumption in the field is that there are conditioned reflex paths connecting sense organ and the motor cortex via association areas. Lashley's experiments, however, disprove involvement of the motor areas. Further his experiments show that the memory trace cannot be localized anywhere within the nervous system. It is perhaps true that limited regions are essential for learning or retention of a particular activity. But even if there is a limited region, the parts within the region seem to be functionally equivalent.

The frontal, parietal, occipital and temporal areas of the cortex are considered as associative areas because of their anatomic relations and these are considered as the store house of images of sensations. Lashley suggests that these associative areas are concerned more with the modes of organization than with any specific memory storage. Further these areas seem to be concerned with the general facilitation or maintenance of the level of vigilance. Destruction of these does not lead to amnesia but only to difficulties in the performance of tasks involving abstractions and generalization.

As the parts of a region have equivalent capacity, there may be multiple representation of an event in a region. The pattern of excitation leads to a pattern of activity and this pattern of activity is fully reduplicated throughout an entire functional area, 'much as the surface of a liquid develops an interference pattern of spreading waves when it is disturbed at several points'. Further, Lashley suggests that all the cells of the brain must be assumed to be in constant activity. There is no cell in excess which is reserved as the storage of memories. He would argue that one should not seek for the trace of any activity merely as an isolated connection between the sensory and motor elements. The spatial and temporal axes of the nervous system which underlie the behaviour must be considered as the basis even for the trace of any activity.

The two concepts which Lashley formulated have been already indicated in the foregoing paragraphs. These are the concepts of equipotentiality and mass action. 'Equipotentiality of parts is the capacity of any intact part of a functional area to carry out, with or without reduction in efficiency, the functions that are lost by the destruction of other parts'. This is 'not an absolute property but is subject to the law of mass action whereby the efficiency of performance of an entire complex function may be reduced in proportion to the extent of the brain injury within an area whose parts are not more specialized for one component of the function than for another' (Lashley 1960).

Lashley was a contributor to and adherent of the gestalt psychology. He believed that what the organism perceives is the total pattern and the behaviour is a series of conditioned reflexes. It is tempting to follow the association - connectionistic theories, especially after the discovery of neurons and the synapses. But no simple connectionism can explain the human behaviour and the neurophysiological mechanisms. Localization does not solve the problem of how a part functions in a complex system. Specificity is perhaps there in some measure in the visual area, but it is very much less elsewhere. "Mind" must not be sought in localization as an integrated interaction of processes reflected in an organization of its own. The mental phenomenon must be subjected to an analysis as complete and detailed as that which is being made of neural activities. Only as progress is made in such an analysis and as the picture of the brain's activities is completed, will it be possible to make significant correlations between the two organized systems. Meanwhile, there is no logical or empirical reason for denying the possibility that the correlation may eventually show a complete identity of the two organizations (Lashley 1960).

Lashley considered that the temporal organization of behaviour is the most fundamental and troublesome problem in neurology. (Even now it continues to be so, not only in neurology, but also in psychology and linguistic semantics and conceptualizations). A solution may be found, according to Lashley, if we study the translation of temporal orders of action into spatial patterns and also the reverse in the brain. In such cases the after-discharge of the sensory excitations persist with a spatial distribution in the brain. Language may represent the characteristic integrative functions of the cerebral cortex, but temporal integration is found in all our behaviour. In the associative chain theory an element in the chain excites the next element. When applied to language this approach loses its ground. In a sentence, the order of occurrence of words, one may think, represents the real order of associations of one word with the next. But words in a sentence can have associations not only with their immediate neighbour but also with the remote ones. The different positions of the word "right" in the sentence 'the Millwright on my right thinks it right some conventional rite symbolize the right of every man to write as he pleases' are determined by the meanings which the positions in relation to other words denote, but those meanings are given by other associations than those with the words in the spoken sentence'. Thus 'the individual items of the temporal series do not in themselves have a temporal 'valence' in their associative connections with other elements. The order is imposed by some other agent. ….The order in which the fingers of the musician fall on the keys or fingerboard is determined by the signature of the composition. This gives a set which is not inherent in the association of the individual movements,' (Lashley 1960).

We find that one can easily change the form of expression of the idea and that different word orders may be employed to express the same thought. These indicate that the temporal integration is not inherent in the preliminary organization of the idea. In fact all the elements of an idea must be considered co-temporal. This precludes the possibility that the intention to act or the idea to be expressed determines the serial order. Lashley suggests that the mechanism 'which determines the serial activation of the motor units is relatively independent both of the motor units and of the thought structure'. The evidence for this is found in the mistakes of order, and the slips and interferences which occur in writing and speaking. Then how does the order come into practice?

Lashley suggests that prior to the internal or overt composition of sentence, a whole range of word units is partially activated or readied. Syntax is then impressed on the acts as they occur. There are three things in so far as language is concerned. In the first place we must identify the activation of expressive elements. As said earlier, these elements do not contain the temporal relations. In the second place we must identify the characteristics of the determining tendency. In the third place, we should consider the syntax of the act-'on habitual order or mode of relating the expressive elements; a generalized pattern or schema of integration which may be imposed upon a wide range and a wide variety of specific acts'. The essential problem of the serial order thus is : 'the existence of generalized schemata of action which determine the sequence of specific acts, acts which in themselves or in their associations seem to have no temporal valence' (Lashley 1960). As far as language is concerned, the understanding of speech and the production of speech may involve essentially the same problems. The performance and reaction to a speech event demand that we postulate an after effect or after discharge of the sensory compounds for a significant time following stimulation.

As regards the integration of temporal and spatial systems Lashley suggests that 'the same cells in the visual cortex participate in a great variety of activities. Practically all of the cells of the area must be fired by every visual stimulation, and these same cells must be the ones which retain the visual memories. The conclusion follows that differential responses depend upon the pattern of cells which are excited in combination. The visual cortex is a network of cells of short axon without long interconnections between its parts or with other cortical areas. Its integrative functions are an expression of the properties of such a network. The same conception must be applied to other cortical areas. There are, of course, long association tracts in the cortex'. But Lashley finds that these long associations may be only skeletal structures and that they do not have any special function. The major integrative functions must be assumed to be carried out by the network of cells of short axon. He argues in favour of analyzing the properties of such networks of cells to understand the mechanisms of the cerebral cortex. All the cells in the network must be considered as in constant excitation and are firing; this happens subject to their recovery from the refractory state. Because of this excitation state, mutual interference of circuits takes place and this results in complicated patterns. These complicated patterns get stabilized in the absence of differential stimulation. What happens at any particular point in the system, as at an efferent neuron, not of the transmission of impulses over a restricted path, of which that efferent cell forms a link. 'Perhaps one will be able to isolate the parts of the system, but the isolated parts are influenced by multiplicity of effects, for which no trace may be found in the isolated preparation of an isolated part'.

if we assume that psycholinguistics is concerned with the symbolic activity of human beings, it is all the more important that in such a study the destructional processes of this activity find a crucial place. The psychobiologists like Luria have demonstrated that the study of the destructional processes actually contribute to an understanding of normal human behaviour. A contrast is available, the factors in several cases can be isolated and one can reconstruct the normal behaviour, in the process identifying the relative importance of the factors and the structures that go into the composition of normal human behaviour. Furthermore the analysis of the destructional processes have immediate applicational value in ameliorating the unfortunate conditions of the suffering humanity.

Speech and Hearing is a very special field to which several disciplines contribute their theories, research methods and findings. There are speech disorders which require surgical and clinical operations. But these operations need not lead to the establishment of normal speech. In some cases they do not definitely lead to normal speech. Hence the importance and the need for the speech and hearing expertise apart from the expertise of surgical and clinical fields, psychology and neurophysiology, etc. the speech and hearing expert acquires a knowledge of the neurophysiology of speech pathologies. He acquires a competence in the psychological analysis of the speech disorders. He can appreciate the role of other psychological factors involved in the maintenance and destruction of speech. He acquires a sound knowledge of the physical aspects of sounds both at the production and auditory levels. He has a knowledge of linguistics, language history of the patients etc., which enable him to diagnose a patient linguistically and set before himself formal linguistic objectives.

Speech pathology is the study of abnormalities of speech-speech disorders. There are certain social conventions, neurophysiological bases and psychological reasons for considering someone's speech behaviour at pathological, as speech defects. If a person's voice is not loud enough, as demanded in normal discourses of a community, his speech is considered a defective speech. Inaccurate articulations which are wholly does not follow the rules of his language, which results in his speech not being understood by the speakers of the same language the person's speech is considered a discovered one. Some people do have, from the point of view of listeners, unpleasant voice. Their speech, because of some reasons not fully explainable, is also considered as disordered. We have some intrinsic notions about the quality of speech in terms of its rate of delivery, rhythm, pitch, loudness, timbre, some special sounds with regard to age of persons and their sex. When such expected notions are violated by the 'peculiarity' of individual's speech, then we consider it as defective. Even the accompanying gestures, grimaces, postures and additional noises can lead to someone's speech being considered as a disordered one. In essence, in a defective speech the listener's attention is distraced from the subject matter of the discourse to its mechanical mode of delivery.

The speech and hearing expert does not consider every speech defect a disorder. If the defects stem from neurophysiological, physiological and anatomical bases, they will be considered as disorders.

The literature on conditions that facilitate acquisition and performance of normal speech does not indicate firm grounds, which help speech facility. However, some experts consider that better physical strength, early establishment of right handedness, type of intelligence (humanistic, artistic and linguistic talents) and tendency to appreciate and enjoy music help the speech facility. Acquisition and performance of speech are not facilitated if the individual has poor physical strength, no clear establishment of right handedness, tendency to acquire, appreciate and enjoy mathematics and sciences (Q-type of intelligence) and lack of interest in music. The role and function of the above in the development and maintenance of speech facility are quite controversial. Speech defects are found in both groups, although certain forms of speech disorders such as stuttering are found more among the male population.

The speech disorders may have their bases in the central and peripheral nervous systems. However, the speech and hearing experts insist that one should not jump to conclusion as to the structural bases of any disorder. A proper investigation may show that a disorder is due simply to psychological factors and that it does not require surgical and clinical operations. Hence a cautious approach taking a comprehensive view of the etiological conditions is absolutely necessary.

It is indeed difficult to characterize a voice as a disordered one purely on objective criteria. Certain social and cultural conventions play a vital role in deciding upon the quality of voice. Generally we consider a voice as defective if it has no adequate loudness, clearness of tone, when its pitch does not match the expectations for the sex and the age, when there is no proper movement of pitch to be followed in a language. Such vocal defects are called dysphonia or aphonia. In dysphonia we have vocal defects and yet one retains the voice. In aphonia one loses the voice.

It would be interesting indeed to study how social and cultural conventions characterize a voice as pleasant, unpleasant, mellifluous and so on. When a voice lacks vibrato, one may call it metallic, flat or hard etc. Inappropriate pitch levels to the age and sex may invite a characterization as high, shrill, etc. irregular vibrato leads one to characterize a voice as tremulous and so on. A thin voice is that which lacks adequate loudness. A husky voice is that which lacks clearness of tone.

There can be structural, neuropathological and emotional disorders and improper vocal habits can also contribute to dysphonia.

In maintaining the quality of voice the glottis plays a very significant role. The glottis should have properly formed edges which can be brought close together. When the edges are brought close together it should allow the escape of any air only when brought about by chest pressure. Further they should be brought together in such a way that it would allow the free movement of the bands when vibrated by the air stream. In a normal situation the throat and the mouth are kept open enough to achieve proper resonance of the tone. When these are not obtained, we get defective speech based on the deformities of the glottis. The deformities do not allow for proper flow of air as demanded.

Anatomically there may be some firm of growths on the cords which lead to improper approximations. When the bands show active pathology, the expert does not give voice training. When the bands show irremediable irregularities, no surgery or medicine can help. Voice sensory-motor control of the voice through ear training drills. They may be encouraged to learn to adjust the larynx. Relief may be extended to people whose bands have irregularities as a result of the misuse of voice. Persons such as singers, auctioneers, and public speakers belong to this category and can be treated successfully.

Another phenomenon which is often considered as dysphonia is the carry over of the high pitched voice of the childhood into adolescence and even adulthood. There are many psychological factors that induce the boy to retain his high pitched voice. Ultimately he gives up the high-pitched voice and acquires an adult voice. When the boy reaches puberty the glottis becomes bigger and lengthened. In this process the boy's voice gets a lower pitch, almost one half of the pubescent rate of frequency. Several boys, however, do not make the grade and continue to prefer the high-pitched voice, though they have had an option to adopt either the high-pitched or the low-pitched voice. This may be due to the premature setting in of the pubescence and/or the unusual lengthening of the vocal cords. The premature development leads to the emergence of a sort of husky voice not appropriate to his age level and not found among his mates. To avoid embarrassment the boy may choose the high pitched voice which sets in so heavily in his speech habits that he cannot give it up even after the entry into adolescence and adulthood. The therapy will be a psycho-therapy, kindling in the individual a desire to change his voice. Intensive training is followed.

Cleft palate is a congenital deformity. There may be a hiatus along the central seam of the palate. Or there may be a gap on the alveolar border and the related structure of the lip. The first one is cleft palate and the second one is usually called a harelip or cleftlip. One must first establish a control over the opening into the nasal chamber. Only then sufficient pressure can be built up in the mouth to produce sounds such as plosives, fricatives and sibilants. The therapists will try to eliminate excessive nasality and sharpen the discriminations between the consonants. He will also try to eliminate the usually accompanying movements and sounds, the patient has developed as substitutions.

In another speech disorder obstructional of the nasal passage causes the patient to produce corresponding consonant stops for the nasals. The hypertrophy of the pharyngeal tonsil can lead to this condition. The patient tends not to use the nasapharyngeal sphincter, as he is able to build up air pressure in the mouth cavity without using the sphincter. And this leads him to develop the habit of speaking without involving the velum. This nasal obstruction can be removed by surgical and clinical operations to certain extent. However, such operations are only a step forward in the actual treatment of the disorder. Intensive speech training is necessary to bring in normalcy. The speech habits acquired earlier can be eliminated only by intensive speech training. Complete elimination is not guaranteed.

In addition to the above disorders based on structural deformities, the experts include the following also : openbite in which the upper and lower lip incisors do not meet each other. This leads to the defective nature of the fricative sounds produced ; short chin causes incorrect articulations of bilabials and sibilants. In prognathic mandible condition, the patient has difficulty with the control of his jaws. He must adjust his speech habits for the production of fricative sounds. A narrow and pointed roof of the mouth can also lead to the defective production of sibilants.

In stuttering we have muscular spasms which interfere with speech. The spasms can be of repetitive (clonic) or continuous (tonic nature). The vocalization and articulation of speech are repetitions and these consist of hesitations. The stutterer gives a feeling that he is engaged in a struggle to overcome the spasms. Such struggles increase in social tensions. The spasms can spread to other muscles also in acute and advanced cases of stuttering. The stutterer thus has a laboured and tense voice, because of his muscular hypertonicity. The stuttering is found more among the boys than among the girls. The incidence is high in the age range of 5 to 10 years. There is rather a rapid decrease as puberty age is approached. Perhaps the higher incidence of stuttering among the males may be ascribed to the comparatively late development of language in the males. Stuttering can be acquired socially, through heredity or by imitation. The stutterer's blood seems to contain more animal sugar than the blood of the non-stutterer and they are found more often in families which have multiple births. They are also found more often in families which have left-handers. Further, stutterers are found more often in families which are susceptible for allergies.

Stuttering can be caused by the anxiety a child develop when his clumsy speech is ridiculed as stuttering by his playmates, parents and other contacts. It may be also a hysterical phenomenon to gain the attention of parents and others. It may be a result of sexual immaturity and/or a phenomenon seeking compensation for fear, etc. Experts consider that stuttering may be a result of conflicts of control between the right and the left cerebral hemispheres. It may be due also to the delayed development of the myelin sheath of the nervous system. It is found that the myelin sheath develops and grows faster in girls than in boys.

The jerky and involuntary speech, called chorea speech, is found among the girls. Stuttering occurs usually before puberty and the chorea speech occurs usually after puberty. The chorea speech is of repetitive nature.

Bulbar polio is due to the damage caused to the peripheral nerves which control the muscles of articulation. One notices stiffness of the neck, fever, muscular pain and severe head ache. The speech disturbance is noticed only after the sickness with the above symptoms runs into a full course. Bulbar polio can disturb the already formed speech habits and it can also arrest further development. The speech disorders which have their bases in the central nervous system include the following : encephalitis, neurosyphilis, chronic subdural hematoma, intra cranial aneurysm, cerebral abscess and glioma. Encephalitis is caused by the inflammation of the brain which usually occurs from the second to fourth decade. Articulation as well as the function of language are disturbed. Syphilis in the blood stream causes the neurosyphilis. The speech is disturbed by dysarthria as well as by other emotional and aphasic disorders. In chronic subdural hematoma, a cyst of blood tumor occurs under the covering of the brain, which may press the brain down and cause a paralysis. This cause disturbance in the articulation of speech as well as in the use of language. The cerebral abscess is like a boil which presses upon the tissues of the brain. Glioma is a type of tumor which can cause articulatory incoordinations.

Aphasia is the term we often use to denote the impairment of the faculty of using or understanding language, both spoken and written. Linguistic impairments can be congential or non-congential. Infantile aphasia is classified into four major types. These are aphasia proper in which there is a deficit of spoken language. This is often called motor aphasia. In the auditory aphasia there is deficit of the hearing of the language. In alexia the patient is unable to read the language. In agraphia, the patient is unable to write the language. The patient is unable to read the language not because of impairment in his vision. The patient is unable to write the language not because of paralysis of fingers. It is the faculty which underlies language performance that must be considered as the basis of the aphasic conditions. Paralysis of the tongue, peripheral deafness, blindness and the paralysis of the fingers are not considered as factors which decide the description of a disorder as aphasia. The etiology of aphasia is traced generally to the underdevelopment and damage of language centers in the cerebrum. Feeblemindedness can result in aphasoid which is characterized by paucity of vocabulary and defective syntax. In infantile schizophrenia, the patient has a tendency to withdraw inwardly from his social contacts. He may understand what is said to him. Yet he may have no desire to reply to what is spoken. These two cases are also considered wrongly as constituting aphasia.

Deficiencies of hearing also lead to communicative disorders. A child may not be able to receive and comprehend what is told to him. He may have also difficulty in monitoring his own speech. There are three kinds of deficiencies of hearing. Technically speaking an individual is considered as a deaf person if he has been unable to hear speech from birth or early infancy. This person has no linguistic memory or impression at all. There is no habit of any oral communication. We consider an individual as a deafened person if he once heard speech in a normal fashion, but is now unable to hear it. We consider an individual as hard of hearing if he can hear speech but his efficiency in hearing is lower than the normal standards.

A deaf child as defined above has severe impairments both in his reception and production of speech. The rate of impairment in the deafened child depends upon the degree of deafening of the child. When a child is hard of hearing, he has difficulty in understanding what he hears. He has no difficulty, however, in monitoring his own speech. There are three kinds of deafness on the basis of etiological factors. These are mechanical or conduction deafness in which the impairment is due to defects in the receiving and transmitting portions in the canal of the outer ear, in the ear drum or middle ear; cochlear deafness in which the impairment is related to the transmission of mechanical sounds into neutral stimuli and/or to the sensory end organs of the acoustic nerve, and, nerve deafness in which there is defect in the acoustic nerve or in the efferent nerves that carry signals from the cochlea to the auditory centers of the cerebrum. There can be also some non-organic deafness related to psychogenic factors.

Perception and conduction deafness are the forms of reduced acuity. The patient produces his speech in a subdued volume in the conduction deafness whereas he produces shouts in the perception deafness hears his own voice louder than it really is. He feels that others are speaking in low voice. Hence he begins to reduce the volume.

we have thus far presented the neurophysiology of speech, three approaches to the description and explanation of the neurophysiology and psychology of speech and have given certain kinds of speech disorders from the speech and hearing experts' point of view. In this section we present the language disorders from the linguists' view point.

Linguists may also consider the neurophysiological bases of speech in order to characterize the speech disorders. However, they can describe speech disorders even without reference to the neurophysiological, psychological and other bases. They consider the speech of a child as delayed if the development of speech in that child is not commensurate with the normal development of the chronological age. When the children are not in a position to follow and produce the patterns of the language while learning the language, their speech may be described as disordered. These disorders of speech can occur in all the language levels a linguist posits for language. Thus one can have disorders at the phonological level, at the morphological and syntactic levels and also at the semantic level. The disorders can be looked at again from the point of view of language skills. Thus the disorders may be related to listening, speaking, reading and writing skills.

At the phonological level the speech is considered defective if a child does not follow the phonological patterns, omitting certain sounds, submitting certain others for the original sounds of a language, and also distorting the sounds of a language. At the morphological and syntactic levels the child may have difficulty in comprehending the discourses. The child may have normal hearing capacity and may understand the single words quite well. But he may not be able to produce the patterns correctly. He may miss the sequence of words; he may omit words and employ incorrect morphological constructions. At the semantic level he may have difficulty in comprehending even the normal vocabulary items. He may not be able to make a proper choice of the lexical items; violate selectional and categorization rules more often than normal children. (See Chomsky 1965 for an explication of these types of rules).

Disorders of reading may be due to lack of proper instruction and opportunity, poor attention, difficulty in perception, reduced vocabulary, and acquisition of non-standard manner of using linguistic items. It may also be due to neurophysiological reasons. Disorders of spelling may result from the disorder of reading. In writing the child transfers the speech into a graphic form. For writing to be an effective medium, it must be developed into a synthesis of movements and concepts. Lack of such synthesis may be considered as a disorder along with the child's improper hand movements, illegible handwriting, failure to produce coherent sentences in writing and so on.

Here we will not present any of the techniques we have for proper therapy or for simple training. Elucidation of such techniques and applications is beyond the scope of the present work. In fact applications of linguistics have not been developed, elucidated and explained with reference to their potential and rationale for use in speech therapy by linguists. Linguistic applications are assumed generally to be beyond the domains of linguists. We shall, however, point out how theories of linguistics can influence work on speech disorders. Before taking it up, it will not be out of place to report on Roman Jakobson's contributions to the analysis of speech impairments.

Of all the linguists Roman Jakobson is the one and perhaps the only one who, during his six decades of chequered linguistics career, has been consistently showing interest in the studies of language disorders. He links these disorders with the process of language acquisition and shows that there is a very intimate relationship between problems of normal language in operation and the disintegration of language as revealed by the different types of aphasic impairments. Because of this intimate relationship Jakobson asserts that linguists have more than a marginal role to play in the studies of language disorders, particularly in the study of aphasia. He finds that aphasic impairments have their own order, a hierarchy of disorders. It is the science of language that will be of immediate assistance in providing tentative answers to the kinds of aphasia encountered in a particular case, as the verbal disturbances do not present a unitary type but differ widely in quantitative and qualitative scales among themselves.

There are two factors, namely selection and combination, which characterize a normal language in operation. The selection of linguistic entities in normal language is based upon the internal relationships that exists between the entities. These relationships may be in terms of likeness, similitude, equivalence, resemblance, analogy, diverse grades of specification and contrast. The combination is the external relation of contiguity that exists between forms, relatable in terms of neighbourhood, proximity and remoteness, subordination and coordination. The aphasic disturbances also may be profitably looked at from the point of view of these two factors.

Jakobson, in fact, identifies three dichotomies as underlying the cardinal types of aphasia characterized by Luria and others. There are (i) combination which implies continuity and affects primarily encodement versus selection, (ii) successivity versus simultaneity and (iii) disintegration versus limitation. We shall see the implication of these dichotomies when we present below the cardinal types of aphasic impairments.

Drawing illustrations from the works and publications of Luria and others, Jakobson builds his own linguistic interpretations of a aphasic impairments. He suggests that Luria's basic classification of aphasic into six types of impairments holds good even from the linguistic angle. Of these, two basic types clearly exemplify the combination and selection dichotomy. The combination and selection dichotomy is viewed also from the point of differences between encoding and decoding or motor and sensory as done by other scholars. The six types of aphasic impairments are - (i) efferent aphasia, (ii) sensory aphasia, (iii) amnesic aphasia.

In efferent aphasia which is a basic type of encoding disorder words are preserved but the patient has a lot of difficulty in the construction of sentences. These words are generally independent of contexts and are mainly substantive concrete nouns. Purely grammatical words disappear. These purely grammatical words include connectives (conjunctions and pre-positions) as well as pronouns. The preservation and retention of a word in this disorder is related directly to its independent status-whether such a word can occur independently without purely grammatical props. Hence nouns are preserved better than verbs. Only the nominative case survives the impairment. Verbs are preserved in their most nominalized form. If a language has both an infinitive form and a finite form of verb, it is the infinite form which shows higher resistance in efferent aphasia. The speech of the aphasic is now more like the telegraphic style. His utterances tend to be reduced tone word sentences. In the phonological level, the phonemes are preserved, but the aphasic exhibits difficulty in making the combinations of phonemes. He shows difficulty in the transition from one phoneme to another. He makes an intensive use of phonemic assimilation and dissimilation. 'The more independent a phoneme or distinctive feature is in respect to the context, the greater the probability of its survival'. The prosodic features are more affected than the inherent distinctive features of phonemes, as the former involve interphonemic relations.

The efferent aphasia thus involves impairment of contiguity, and is a typical contiguity disorder. This contiguity disorder is noticed on all levels of language. The root is better preserved than the suffixes. The main deficiency relates to the loss of ability to construct proposition through a construction of sentences.

If sentence construction is the major deficiency in the efferent aphasic, it is the preservation of independent words that becomes the major deficiency in the sensory aphasic. The sentence wholes are preserved, that is, the sentence pattern is in tact. This is made possible because the grammatical words such as connectives, and pronouns are preserved and such preservation provides the patterns easily. To a sensory aphasic it is the initial substance that poses the greatest difficulty. Hence in languages where the subject appears at the beginning of a sentence, the predicate is more easily retained. The abolition of subject is more prominent and more certain when the subject is a pure lexical items in its primary form occurring with a minimum of dependence on the context. The aphasic will have greatest difficulty in constructing an equational type of sentence. He will have difficulty in naming objects.

In the phonological level, the sensory aphasic preserves the combinations of phonemes. However, he simplifies some phonemes within the combinations. Such simplification involves mainly those phonemes which cannot be predicted from their environment. The major loss in the phonological level is the total loss of certain phonemic distinctions. It is the phonemic perception and not the physical production that characterizes the sensory aphasic. The phonologic defects of the sensory aphasic are related to the hierarchical structure of the phonemic patterns. One can certainly identify the order of deficits, their hierarchical order.

The two basic of aphasia, namely, the combination and selection are closely related to encoding and decoding impairments. The combination disturbances hamper the construction of a context, the encoding activity, as sentence construction is seriously impaired. The selection disturbances hamper the analysis of a context into its constituents, as sentence wholes are retained but a further breakdown into constituent elements is not achieved.

Jakobson believes that the constituents are intact in the encoding activity because the speaker makes the selection of the elements before combining them into a whole. In the decoding activity the decoder has to grasp the whole first and then proceeds with the constituent analysis. 'The decoder is a probabilist to a much greater extent than the encoder'. For the encoder the selection of items into a whole. For the decoder, the grasping of the whole is the first stage which is followed by an analysis of the constituents. Hence Jakobson finds that in both the basic types of aphasia the first and primary stage is more viable and stable than the second and secondary stage. Yet there is no pure encoding or decoding impairment. The impairment is generally predominantly encoding or predominantly decoding. Between decoding and encoding it is decoding that seems to occur more independently. Decoding depends less upon encoding than vice versa. The recorded cases clearly demonstrate the wider occurrence of decoding action than the encoding activity. Agrammatism is the pivotal sign of efferent speech, external utterances are produced. Impairment of internal speech is noticed in the efferent aphasia. The sensory aphasia leads to an incapacity for metalingual operations which include paraphrasing, use of synonyms and intralingual translation.

The third type of aphasia is called dynamic aphasia. The dynamic aphasic resembles the efferent aphasic in many respects, because dynamic aphasia is also a combination disorder. But the aphasic's difficulty is not with regard to combination of phonemes or with regard to the combination of words in a sentence. The dynamic aphasic fails to combine sentences which have no hierarchical grammatical rules within a set of utterances. Thus the dynamic aphasic has a lot of difficulty in constructing discourse and to build a monologue, 'a context which is incumbent on the speaker alone'. He is unable to switch from one system of signs to another such as answering a verbal order by a prescribed gesture.

Just as dynamic aphasia reflects a more intricate efferent aphasia, the semantic aphasia reflects a higher order sensory aphasia. The semantic aphasic cannot grasp the difference between phrases such as wife's brother and brother's wife. The semantic aphasia reflects a highly attenuated form of sensory aphasia. The word order is uniform and inflexible. The organization of a sentence pattern is easy for the semantic aphasia. However, comprehension of a word is in direct proportion to its syntactic environment. Morphology, in the words of Jakobson, yields to syntax. Morphology of lexical items is completely lost on the semantic aphasia.

The afferent or kinesthetic aphasia is based on a disruption of the capacity for combination and hence should be considered as an encoding disturbance. The afferent aphasic however makes a merger of phonemes - not a mere assimilation. His failure to combine appropriate features into a phoneme results in overlapping and merger. He has difficulty in the combination of distinctive features into a phoneme. The aphasic finds it difficult to use the bundle of all the concurrent features essential for a phoneme and utilizes only one or a few features of the given phoneme which by now shows a merger with one or more phonemes. There is no constancy however is the repertory of preserved features and the terms of any binary opposition are mutually inter-changeable. The afferent aphasia thus does not exhibit the correspondence between the dichotomy of combination and selection, or between encoding and decoding.

In the amnesic aphasia the patient is unable to make an appropriate selection. But this inability is more particularly affecting iterative selection. The patient points correctly to his eye when asked to do so. When asked to point out his eye and ear, he points correctly to the first item and either omits the second or shows a wrong organ. When asked to point out eye, ear and nose in a sequence he is simply perplexed. In the grammatical level the coordinative constructions are the only ones which suffer in the amnesia aphasia.

Jakobson's main contribution is the clarity with which he classified the aphasic impairments purely on linguistic levels. The lingustic level envisaged by Jakobson is an all comprehensive approach, not a mere structuralist position. The level included phonological, morphological, syntactic, semantic and inter and intralingual communication with their attendant discourse and paraphrasing capabilities. Jakobson's contribution does not stop with a mere linguistic characterization of aphasic impairments on purely linguistic levels, but to take it to a higher inter-disciplinary interpretation.

Jakobson suggests two stages of analysis and pursuit for every scientific endeavour. Autonomy of approach is an essential first step for a proper perspective and scientific analysis of any phenomenon. At the same time autonomy is rewarding but isolation is harmful. After an autonomous analysis of a phenomenon from the point of view of a single discipline, it is useful and even necessary to look for correlation of facts identified by different disciplines for the same phenomenon. The need for such a correlation is much more urgent and fruitful for an investigation of language disorders as these disorders have a definite but difficult to localize bases in the neurophysiological make up of man.

Jakobson suggests a tentative topographic analogue to all the three linguistic dichotomies identified by him :

Combination Disorder	More anterior lesions of the cortex
Selection Disorder	More posterior lesions of the cortex
Efferent Disorder	Anterotemporal lesions
Sensory Disorder	Posterotemporal lesions
Dynamic impairment	The frontal intrinsic area of the forebrain
Semantic impairment	The posterior intrinsic area (the posteroparietal and parieto-occipital sections).

the behaviourist approach to language characterizes language as consisting of a set of complex verbal responses. These responses are conditioned by environmental reinforcement. There are two types of conditioning-classical and operant. In ameliorating the conditions of speech disorders, the clinical procedure following the behaviourist school insists upon repeated imitative tasks in which the rewards are awarded for the correct responses. The pattern of responses is progressively shaped and led to form more complex and more differentiating patterns. Sequencing of the events for the imitative tasks, and the elicitations are carefully planned in such a way that there is a slow but steady withdrawal of rewards with commensurate increase in the non-imitative responses. Each step is considered a programme by itself and the clinician proceeds from one step to the other only when the patient has mastered the first step. The behaviourist may also use the developmental schedules available for language in their clinical work.

In the behaviourist approach the emphasis is on the child's imitative learning. If the child produces an utterance, comprehension is assumed to have been achieved. Gradation of linguistic structures, in this approach encourages the identification of nouns as the first step, followed by naming of objects and pictures, the locative pre or post positions and so on. The aim is to enable the child to acquire the basic elements of a language in all its levels, with the assumption that with such an acquisition of basic elements the child will be in a position to develop his language on his own initiative.

Language acquisition is viewed as the learning of responses. These responses are reinforced by rewards ; the rewards are given by a listener through comprehension, environmental control, social approval and other actions. They reinforce the responses and the responses become generalized linguistic rules. The reinforcement schedule includes reinforcement of many items that are not, properly speaking, linguistic; but these are highly essential non-linguistic props for the acquisition of language. These include rewards for sitting still, contacting the eyes of the clinician and imitating simple motor acts. Vocal imitation of vowels and consonants and repetition of words and phrases immediately follow the above. On the receptive side, pointing to objects, body parts and environmental conditions form the responses. Such responses are also carefully graded. They are followed by the development of receptive responses to simple commands. In the production side labeling plays an important role and in the receptive side recognition has a prominent place. A useful and very crucial linkage is presented to the child through games such as naming missing objects. Storage and retrieval part of language capacity is aimed at in these exercises. The when, where, how and why of things and events come later on, which aim at making discourses in real language use situations.

The problem a clinician faces in a speech clinic is similar in many respects to the one a second language teacher faces in his classroom. The patient is trained in the clinic so that he will freely use this training outside. The problems of performance outside the clinic thus must be reflected in the training programme pursued in the clinic. Many a programme does not, however, recognize this fact. Some however incorporate conversational and/or playgroup activities. Questions and answers are presented as language tasks. The role of imitation is reduced to some extent. In India programmes are few in number, publications of literature are still a rarity, communication between scholars still carried out in terms of work on languages of the west, and works based on Indian languages are yet to be firmly established. Emphasis is on expression system rather than comprehension. Yet language performance outside the clinic continues to receive only scant attention.

the mentalist linguist's approach to language disorders and their clinical amelioration emphasizes the developmental schedule of language acquisition. He sequential amelioration steps closely parallel the normal language acquisition developmental schedule. Comprehension is considered basic and a pre-requisite to speech production. Normal children have more receptive than productive power. Furthermore acquisition capacity for comprehension is accomplished much earlier and is more elaborate than capacity for production. As a corollary the relevance and importance of imitation should be considered marginal. The performance of the patient outside the clinic has a direct bearing on the ameliorative training administered in the clinic. The mentalist records not only what the patients says, but also what the normal users of the language say as well as the activity the patient is engaged in. Unlike the behaviourist linguist-inspired clinician concentrates on syntactic and semantic aspects along with phonological factors. The mentalist linguist-inspired clinician assumes that grammatical analysis of early speech will help early diagnosis which is distinct from language delay. This has resulted in the construction of several developmental tests such as Berry-Talbott Exploratory test of Grammar, North Western Syntax Screening Test and others. The mentalist clinician's major problem is the interpretation and use of diverse and at times disparaging developments within the mentalist school to his own advantage. The rapid changes that take place in theory are a challenge to his nerve and skill. For some models and assumptions of linguistics and learning theories, see Thirumalai (forthcoming).

To conclude, the aspects of language acquisition by normal children form a relevant and very useful backdrop for the ameliorative steps. The various models of linguistics, neurophysiology and learning theories should be carefully understood, properly integrated and/or differentiated to achieve the best possible results.

The study of language, disorders and of the neurophysiological mechanisms of language production, use and comprehension is yet to find its due place in the discipline of linguistics. The students of linguistics and psycholinguistics will benefit a lot from an understanding of the neurophysiological mechanisms and language disorders. Linguists can contribute to scientific appraisal and evolution of ameliorative steps badly needed to alleviate the suffering of speech patients. Brain (1961) and Perkins (1971) give a good introduction to the types of speech disorders. Luchsinger and Arnold (1965) may be also referred to. Penfield and Roberts (1959) is another important volume. Jakobson (1971) gives aspects of aphasia. Berry (1969) gives language disorders of children and suggests several ameliorative for an indepth study of the positions of Luria and Lashley. Hebb's Organization of Behaviour. (Hebb 1949) is a classic that must be read. For an understanding of speech disorders and the practices of therapy, Berry and Eisenson (1970) is recommended. Reuck, and O'connor (1964) is an excellent collection on disorders of language. Cherry (1957) and Miller (1970) give aspects of the psychology of communication. For auditory perception and acoustic perception of speech and communicative competence we have already cited some references.