WORD-DEAFNESS is a special morbid psycho-sensory state in which the sounds of language lose their significance for the patient. The sense of hearing is preserved for common sounds, and even music in certain cases; words are heard, but not understood. A patient of mine having this symptom used to say, “If I go to a lecture or hear a sermon, I hear the speaker, but what he says is all Greek to me.” On the other hand, this gentleman could go to a concert and understand the musical notes. This condition occurs as a part of the symptom-group aphasia, or it may show itself independently in the course of limited cerebral cortical degenerations. The lesion causing word-deafness is usually found in the left hemisphere, in the first and second temporal gyri, or it may be in the inferior parietal lobule and gyrus supra-marginalis, penetrating deeply enough to injure fasciculi going into the temporal lobe. It would appear, from the evidence now before us, that the centre for psychic hearing is in the caudo-dorsal part of the temporal lobe.
WORD-BLINDNESS, or alexia, is another special morbid psycho-sensory state, in which the visible signs of language lose their significance for the patient. Usually there is no impairment of sight; the patient can see the letters and words as objects, but he cannot read them at all, or must do so letter by letter. Even numerals and pictures of objects in some cases become unintelligible. In testing for this condition a possible confusion with verbal amnesia must not be forgotten. In such a case the patient knows the word or object, but cannot name it; usually he can, however, inform us by signs or indirect expressions that he takes proper cognizance of the object. Alexia is present in a certain proportion of cases of aphasia, and it may be complicated with lateral hemianopia. The exact seat of the lesion producing alexia is at present unknown. Theoretically, however, we must place it in the course of paths from the cortical visual area (cuneus and adjacent gyri) to the general speech-centre. Psychic blindness for objects in general (soul-blindness of the Germans) is now quite conclusively proved to be due to degeneration of both occipital lobes, more especially their mesal gyri, where the visual centres are. This psycho-sensory state, with the accompanying cortical changes, has been demonstrated in cases of dementia paralytica.
APHASIA, or loss of the faculty of language, is so important a symptom as to deserve elaborate consideration in a separate article of this volume; and to it the reader is referred. Suffice it here to state that aphasia may be classified into three forms: (1) Sensory aphasia, in which there is primary disorder of the psycho-sensory (perceptive or centripetal) part of the complex central mechanism for speech; (2) Motor aphasia (including ataxic aphasia), in which the primary lesion affects the motor (expressive or centrifugal) parts of the mechanism; (3) Amnesic aphasia, in which loss of memory (effacement of residua) of words and signs is the prime condition.
II. Sensory Symptoms.
HYPERÆSTHESIA is a condition of exalted excitability in the various parts of the sensory apparatus: terminal nervous organs, nerve-trunks, central gray matter. We may admit such a state as existing independently of consciousness, as where a lesion cuts off communication between the perceptive cerebral centres and the periphery, but in practice we consider only conscious hyperæsthesia. In this state the subject may be able to perceive (feel) slighter impacts than would affect a normal individual, or he receives an exaggerated, usually unpleasant, impression from ordinary excitations. It may also be said that hyperæsthesia exists as a purely subjective state, psycho-sensory hyperæsthesia, without external mechanical excitations.
(a) Hyperæsthesia of common tactile sensibility in the skin and mucous membranes is frequent. The least touch is felt with unpleasant acuteness and causes unusual reactions of a reflex order; frequently, but not necessarily always, a sensation of pain is produced at the same time. It has been claimed that in certain cases the points of the æsthesiometer could be perceived (distinguished as two points) at smaller distances than the average normal, but I have never been able to demonstrate this to my satisfaction. The simplest form of tactile hyperæsthesia is met with in persons of a highly nervous organization, in those under the influence of strong emotions, in the hypnotic state, and while intoxicated. The common pathological conditions in which increased sensibility is found are meningitis (cerebral and spinal), hydrophobia, tetanus, neuritis, dermatitis, hysteria, and spinal irritation; also in connection with inflammations and traumatisms.
(b) Hyperalgesia, often coinciding with (a), is that condition in which pain is produced by excitations so slight that they would not affect a healthy nervous apparatus: it is commonly designated as tenderness. Acute and dull, superficial and deep tenderness should be sought for and distinguished, as having different values in diagnosis. A type of deep tenderness is that found upon pressing steadily upon a diseased nerve-trunk. Acute superficial hyperalgesia is best studied in cases of trigeminal neuralgia and spinal irritation. Occasionally, universal hyperalgesia is met with, usually in hysterical women.
(c) Hyperæsthesia to thermal impressions is ordinarily shown with reference to cold. In cases of neuralgia or neuritis cold is felt excessively and painfully; in some cases of posterior spinal sclerosis there is the greatest dread of draughts of cold air, and patients protect their legs in an extraordinary manner.
(d) Hyperæsthesia of the muscular sense.3 The special sensations or notions of muscular states and activities which we possess may be considerably exalted, as shown by greater delicacy and rapidity of movements, and by the abnormally acute way in which perceptions of form and dimensions are obtained by the subject without assistance from other senses. Examples of this condition are met with in hysteria and hypnotism.
3 This term is employed as clinically sufficient. It is impossible in this article to enter into a consideration of the various theories held with reference to the function in question, whether it be psycho-motor, psycho-sensory, or a true muscular sensibility. It certainly differs much from the various forms of common sensibility, and has special paths.