Aphasia

Aphasia {{fn|1}} (from Greek α, privative, and φασις, speech) is a term which means literally inability to speak, and is used to denote various defects in the comprehension and expression of both spoken and written language which result from lesions of the brain. Aphasic disorders may be classed in two groups:--first, receptive or sensory aphasia, which comprises (a) inability to understand spoken language (auditory aphasia), and (b) inability to read (visual aphasia, or alexia); second, emissive or motor aphasia, under which category are included (a) inability to speak (motor vocal aphasia, or aphemia}, and (b) inability to write (motor graphic aphasia, or agraphia). It has been shown that each of these defects is produced by destruction of a special region of the cortex of the brain. These regions, which are termed the speech centres, are, in right-handed people, situated in the left cerebral hemisphere; this is the reason why aphasia is so commonly associated with paralysis of the right side of the body.

Related Topics:
Greek - Language - Lesions of the brain - Left cerebral hemisphere

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A study of the acquisition of the faculty of speech throws light upon the education of the speech centres, and helps to elucidate their physiological interaction and the phenomena of aphasia. The auditory speech centre is the first to show signs of functional activity, for within a few months of birth the child begins to understand spoken language. Some months later the motor vocal speech centre begins to functionate. The memories of the auditory word images which are stored up in the auditory speech centre play a most important part in the process of learning to speak. The child born deaf grows up mute. The visual speech centre comes into activity when the child is taught to read. Again, when he learns to write and thus begins to educate his graphic centre, he is constantly calling upon his visual speech centre for the visual images of the words he wishes to produce. From these remarks it will be seen that there is a very intimate association between the auditory speech centre and the motor vocal speech centre, also between the visual speech centre and the graphic centre.

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