Disorders of taste are for the most part neither as varied nor as bizarre as the abnormal conditions of the more complex senses. Illusions of taste, hallucinations, and subjective tastes we have already referred to as frequently found. But of them little can be said, except that they occur, and that they present very little of psychological interest. The appearance of these subjective tastes may in some cases be due merely to the fact that “a taste sensation easily associates itself with certain muscular sensations. Thus, pressure on the base of the tongue provokes the movements of vomiting. With this muscular sensation may be associated a sensation of bitter, which accompanies violent nausea.” In ways similar to this some observers would explain the reports of others who find taste sensations to be produced by mechanical stimulation of papillæ. Most observers do not get such results, and it may be that these sensations when they are reported are of the associated variety.
In the case of certain abnormal nervous conditions, however, these features may assume rather striking proportions. Thus, in the “auræ,” or preliminary symptoms preceding an epileptic attack, the patient often experiences unpleasant bitter or metallic tastes, and distressing feelings of numbness of tongue, etc. These sensory manifestations are, however, by no means as elaborate as are the “auræ” of some of the other senses, notably hearing and vision.
Conditions of partial or complete ageusia, or loss of taste, are well known. Such conditions may result from the local application of various drugs to the end organs, the paralyzing effect of drugs on the nerve trunks, injury to, or operations on, these nerves, or damage through injury, disintegration, or removal of special brain areas.
In the case of the mentally deranged taste hallucinations are usually disagreeable, and they are often rationalized into a fabric of delusions,—foul gases are said to be blown upon them, poisons are being placed in their food. Such patients behave in realistic manner, making various defensive reactions, such as stuffing the nostrils with paper or cloth, spitting, and refusing food. In some cases these hallucinations of the insane obviously originate from local inflammation in the peripheral tissues, or from glandular disturbances, and, hence, do not in themselves constitute important pathological symptoms. In some cases, however, such hallucinations arise quite independently of such acute local conditions of irritation, as in chronic psychic disorders or dementias. Under such circumstances they have greater significance, as they point to more deep-seated mental and nervous disturbance. Just as in normal life taste and smell are very closely associated with each other, so, in these cases of insane hallucinations, disorders of taste sensation are likely to involve olfactory irregularities as well.
An interesting though apparently somewhat rare phenomenon in the field of sensation is what is known as “synæsthesia.” By this is meant cases in which a given sense quality arouses, or is intimately associated with, qualities belonging to other sensory modes. Thus, in the case of vision and hearing, some individuals perceive the different vowel sounds, or the sound of musical instruments, as having color. One such person reports that to him all the consonant sounds seem to be very dark purple, while among the vowel sounds “a” seems yellow, “e” is pale emerald, and “u” is light dove color.
Taste, far from being an exception in this case, is one of the senses in connection with which “synæsthesias” must often occur. Salt, for instance, is described by one observer as dull red, bitter as brownish, sweet as clear bright red, and sour as green or greenish-blue. To another observer the taste of meats seems red or brown, the taste of Graham bread is rich red in color, while all ice creams (except chocolate and coffee) taste blue. To still another reporter the sound of the word “intelligence” tastes like fresh sliced tomatoes, while the sound of the word “interest” tastes like stewed tomatoes. There has been much speculation as to the probable meaning and mechanism of these synæsthetic experiences. Investigation seems to show that the particular combinations are by no means universal, even among those who report such observations,—they seem to be individual and personal in their nature and presumably in their origin.
It seems quite probable that in the main these synæsthesias represent uncritical confusion of sensory qualities with other sensory qualities, or with the affective qualities, the feelings, which accompany them. Thus, we often hear such phrases as “bright taste,” “heavy taste,” “dark brown taste,” “green taste,” “soft taste,” “hard taste,” “smooth taste,” etc. It is clear in most of these cases that either a touch component is included in the total taste experience (as in “smooth taste,” “soft taste,” “hard taste”), or that kinæsthetic (muscular) factors are so included (as in “heavy taste”), or that the phrase is more or less designedly an analogy, or other figure of speech (as in “sharp taste,” “bright taste,” “clear taste”). The basis of such analogies is sometimes rather easily discerned, and often is seen to be the “feeling tone” which the sensation arouses,—the effect or “affect” which it produces. Thus, a heavy weight retards, inhibits, and overpowers us. Some tastes have this same overpowering affective tone, and may be intelligibly described as “heavy.” A clear, bright day gives us recognizable feelings of pleasantness, relief, and gives to objects a distinctness of contour. Some tastes, being well defined, definitely localized, and highly agreeable and soothing, may, then, be intelligibly described as being “clear,” “bright,” or “pointed.” These illustrations represent, to be sure, only simple forms of such synæsthesias. But even the resemblance of the sound of “intelligence” to the taste of fresh sliced tomatoes is by no means incomprehensible when we reflect that “freshness” means “alertness,” “sliced” suggests sharpness of edge, while tomatoes thus prepared are usually mature and ripe. For are not alertness, keenness, and maturity the very marks of intelligence, just as “dullness” and “greenness,” also sense qualities, are expressive of its absence? In somewhat the same way we commonly speak of “sweet odors,” “sweet sounds of music,” or even sweet visual experiences, as in “a sweet face.”
A few individual cases of taste synæsthesia have been studied in some detail. Such individuals are often shown to have a defective sense of taste and to rely largely, in their recognition of taste, on touch accompaniments, affective characteristics, and such “color” experiences as the various tastes are said to induce.
Under certain unusual organic conditions, and also still more commonly in the case of degenerate and neurotic individuals, various perversions of taste occur. These perversions do not seem to be exclusively gustatory in character, since they involve more general factors, such as appetite, craving, and emotional disturbance. The name parorexia is sometimes given to these perversions of taste and appetite. One of the subforms, known as malacia, takes the form of an urgent desire for hot spices, or for sour and acid foods, such as pickles. What is known as “salt hunger” is a very similar condition, especially often found among the lower animals. Another form of such perversion, known as pica, shows itself in the desire to eat such substances as clay, chalk, and similar gritty or earthy substances. Especially often among children and among certain primitive peoples the chewing of these substances often seems to give a satisfaction quite unfamiliar to the majority of mankind. Little is known about such perversions beyond the fact that they have often been reported.
Under certain conditions of mental degeneracy and nervous disorder perversions sometimes arise which have been classed under the term allotriophagia. This perversion takes the form of eating with apparent relish various kinds of filth which are commonly offensive and disgusting. In these cases it is quite possible that there is no genuine taste disorder. Many, if, indeed, not most, of our revulsions against substances known as filth arise on the basis of associated circumstances, rather than on the simple basis of their taste qualities. The falling away, or deterioration, of these associative and æsthetic controls in the case of the demented and degenerate, and their absence in the case of the feeble-minded and imbecile, may easily lead to reactions which suggest but do not necessarily involve genuine taste disorder.