SPEECH, Defects of. Speech is an ex tremely complex and intricate mechanism, and in the normal adult represents a large number of various factors. Its defects, therefore, are equally complex. In ordinary speech at least three separate types of processes are involved: (1) sensory; (2) motor, and (3) intellectual or associational.
(1) The sensory mechanism of speech in cludes all the avenues by which the idea of a verbally expressible picture can get into the brain. The eye and the ear are mostly used because with these senses the pictures are most distinct, but touch, smell or other sense, if recognized, may be of use in the faculty of speech. Thus with the sensory portion of the speech-mechanism the intellectual factor must necessarily be joined. One sees the words on a printed page and pronounces them; but if written in a script to the reader unknown, he can see the characters and yet will not be able to utter the sounds they represent.
(2) The motor side of speech implies (a) the ability to use the muscles of speech and (b) the power of co-ordinating those muscles so as to say the right things. The lips, the tongue, the larynx, the teeth are the organs mostly used in speech. One may say that in deaf-mutes the hands are organs of speech. The nerves that govern the muscles ordinarily used in speech are the motor cranial nerves, the nuclei of which are located in the medulla oblongata (q.v.) ; but the centre that co-ordi nates their movements with the sensory impres sions which come in through the organs of special sense, as well as with the intellectual concepts concerning the things seen, heard or touched is located in the third frontal convolu tion or Broca's convolution. This is the chief motor centre for speech.
(3) The intellectual factor in speech implies the action of co-ordinating and associational fibres in the human brain that pass from the sensory centres to the motor centres. It is the factor that governs, as it were, the knowledge of what one is saying. One may repeat from the hearing a line of Choctaw, but without understanding it: the intellectual factor is here non-operative. Memory-images of many kinds may be reproduced by appropriate stimuli; and defects in certain parts of the brain interfering with the bringing out of the memory-images by which a sound is associated with its cause, or an object with its name, occasion certain well-defined disorders of speech. The act of speaking, therefore, requires: (a) the power to think or to construct an idea; (b) the capacity to recall and to formulate the word or words which express the idea; (c) the ability to artic ulate the sounds in an understandable or con ventional manner.
It is customary to use the word aphasia to denominate true defects of speech. Defects in the incoming sensory tracts, which must modify speech in some respects, are not usually in cluded in this category. In the same manner defects in nervous supply of the muscles of speech, such as paralysis of the tongue, are not termed aphasia. Again, a purely intellectual defect, as in idiocy, whereby speech is seriously affected, is not classed as aphasic. Seglas has divided the disorders of speech into three groups: (1) dylogias, or the disorders of in telligence which affect speech — as seen in idiots, imbeciles, etc.; (2) dysphasias, or true
affections of speech (aphasias) — the most in teresting and complicated; (3) the dysarthrias or the disorders of articulation — such as are seen in stuttering, in the peculiar speech of deaf-mutes, in the speech of bulbar palsies, of facial paralyses, etc.
The aphasias are the defects of speech that involve the association-tracts and the sense Centres and have been most exhaustively stud ied. Speaking generally, the true aphasias may be classed in three broad groups: (1) the receptive or sensory aphasias, which result from some injury to the centres for sense memories of things heard, seen, smelt, tasted, touched, etc.; (2) the conduction-aphasias, which follow injury to the conducting fibres in the brain that pass from a sense-centre to the motor centre; (3) emissive or motor apha sia, which is produced by an injury to the motor cortex chiefly of Broca's convolution. Some 30 different types of aphasic disorder of speech are known and may be summarized on the chart here given; but some of the com moner forms of aphasia may be mentioned. Of the receptive or sensory type, amnesic apha sia, or word-deafness, is one of the most char acteristic. In all of the sensory aphasias there is a loss of comprehension of the words heard or read. In amnesic aphasia the patient hears very distinctly everything that is said, but it might as well be in a foreign tongue, because of the disorder of the centre for word-memory pic tures in the temporal convolution. The patient usually speaks, but makes many lapses, not knowing just what he is saying and on hearing his own speech not understanding it. Many varieties of this defect are known. They should be studied in special monographs (see chart for varieties). In the conduction or association aphasias or paraphasias, the asso ciation-fibres connecting one speech-centre with another are interfered with. Any of the types may be present, but the form most often seen is one in which the tracts between the auditory centres and the motor speech-centre is in volved. Here the patient is aware. of the words, knows what they mean and tries to speak, but speaks incorrectly; his path seems to be blocked. The commoner type is motor aphasia. In this Broca's convolution is affected. The patient here sees and hears and compre hends, but is unable to speak the words. He is likewise unable, as a rule, to write the words he sees or hears, and hence suffers from agraphia as well. Many common expressions, as *yes* and *no,* orni ng *good bye,* etc., may be retained. The mechanical necessities that underlie many intellectual proc esses are clearly brought out in the study of aphasia; and in no other manner is the knowl edge driven home how dependent one is on the proper working of certain centres and tracts, as II, the study of the defects of speech. Consult Lichtheim, 'Aphasia, Brain> (1895) Elder, 'Aphasia and the Cerebral Speech Mechanism' (1897) ; Bastian, 'Aphasia and Other Speech Defects' (1898) • Pick, 'Proceed ings of 10th International Congress) (Paris 1900); Dejerine, (Semeiologie des Maladies Nerveuses' (1902) ; Baldwin, 'Dictionary of Philosophy and Psychology,' article 'Speech and its Defects' (1902-04) ; Jelliffe and White, 'Diseases of the Nervous System' (3d ed.. 1919).