The Nature and Frequency of Mental Images

It is a familiar fact that in one way or another and in different degrees to different individuals it is possible to have sensory experiences without the actual presence of their accustomed stimuli. Thus, many people can recall “in their mind’s eye” the colors of objects, their shape and structure, when they are no longer in the presence of the object thought of. Or, “in their mind’s ear,” they can hear the blare of a trumpet, the voice of a friend, the hissing of steam, when no corresponding stimulus is present to the ear. Similarly, “in imagination” many can experience the tactual feel of velvet, the odor of onions, the warmth of sunshine, the ache of a tooth, the nausea of seasickness.

“Thus, I can call up in my mind’s eye, more or less vividly, my boyhood home, and seem to see, though more obscurely than if I were present on the spot, the house and barn, the grape arbor, the garden, even my little bookcase in the library. I can smell the honey in the bee boxes, and can hear the general hum and stir of the hive. I can do this because I can call up images of these past experiences. Or, by putting together the images of wheels, sails, birds, and ropes which I have actually seen I can create in my mind’s eye an aeroplane of a pattern which has never yet been constructed.” This constructive performance would constitute “imagination” as distinguished from mere “imagery.”

These images of imagination are not to be confused with the after sensations which we have already described. They may be experienced days, or even years, after the first application of the original stimulus. Nevertheless, these “mental images,” or “centrally excited sensations,” are described as essentially sensory in character—they have the attributes of all sensory experiences, such as intensity, extensity, duration, clearness, locality, quality, and modality. In fact observers have been found for whom these mental images were so realistically sensory that actual negative after sensations, in the case of visual images, have been reported as following upon them.

In the case of many individuals, these experiences of objects in their absence are relatively rare and obscure, and in some cases, indeed, are so obscure as to lead the individual to deny the existence of such experiences. In still other cases the centrally excited sensations, the mental images, are experienced in their vivid and, apparently, immediately sensory form only under special conditions, as in dreams, hallucinations, drowsiness, or fatigue, or under the influence of special drugs. It has appeared from the study of mental images that, in so far as they are present, they are not equally reported in the different modes of sensation. Visual images in some cases, auditory images in other cases, and motor images in still others, have seemed to be so specially frequent, vivid, or easily aroused that at one time it was customary to classify individuals on the basis of their images as visuelles, audiles, motiles, and efforts have even been made to adapt a method of teaching to the presumed “imagery type” of the student. In the present connection our interest is only in inquiring whether and in what degree “images of taste” are present.

Mental Images of Taste

Is there a “gustatory” or taste imagination as well as a visual or an auditory imagination? It should, of course, be borne in mind that tastes may be “thought of,” “referred to,” or “indicated” without there actually being taste qualities present in experience. Thus, I may refer to the “saltiness of the pork” and discuss it in detail without having in consciousness the sensory tang and quality of “salt.” The saltiness may be “represented” in my thinking in this case, not by a taste quality at all, but by the word which stands for such a quality, or even by a visual picture of a white granular substance, or an elongated strip of meat. Only if the immediate and unanalyzable experience of sensory “salt” is present is there evidence, in this case, of an “image of taste.”

Obviously, we must mainly rely in such cases on the testimony of the observer, although there have been investigations made of a more objective sort, in which it is shown that the reported “images” are so similar in character to actual sense experiences that the observer, under appropriate conditions, cannot distinguish between the two.

If we turn to the results of introspection or individual testimony, we find that if taste images exist at all they are at least reported as very much less frequent and vivid than are images from other senses. Thus, one observer, who in the course of two years’ observation of his own experience recorded 2,500 “images,” classified these as follows:

Much the same state of affairs is revealed if one attempts, when certain objects are named, to record the imagery which the name evokes. In response to the word “tornado” some individuals at once report visual appearances of falling houses and waving trees, while others report auditory experiences of crashing buildings and rushing wind. Within a few moments most observers report the appearance of images from various senses, though some of them are more vivid, more prompt, or more enduring than others. In the case of taste, however, it is rare that images are reported as either vivid, prompt, or lasting. Usually when such an image is reported at all it is described as lagging behind the images of other modes, appearing to be dragged in or reënforced by them, and to be transient, weak, and fluctuating. It seems, also, that, although images of taste are not easily aroused directly by words, their appearance is facilitated if a visual image or impression is present with them. Consequently, when the poet or the advertising writer desires to provoke imagined tastes in his readers he often attempts to arouse them more effectively by presenting suggestive pictures of scenes associated with the object, or a tempting array of the articles themselves in an agreeable setting.

Taste in Dreams and in Hallucinations

Reports of the sensory components of dream experiences show taste to be an inconspicuous factor in dream life. The following table shows the results obtained by two independent investigators when dreams of various individuals were analyzed into the sensory elements reported:

Records of the hallucinations of sane and insane people also show taste to play a relatively minor rôle, so far, at least, as frequency of report is concerned. In both cases visual, auditory, tactile, and olfactory hallucinations seem to be more common experiences. “Subjective tastes,” or tastes which do not appear to be caused by the action of any substance in the mouth, are, however, by no means unknown, although in most cases it is apparent that these tastes come from some unsuspected irritation of the taste organs by actual agents. Substances circulating in the blood may often be seen to be responsible for these “subjective tastes.” Thus, in diabetes the excess of sugar in the blood may give rise to a persistent sweet taste, and in case of jaundice biliary products often produce sensations of bitter. Various drugs, when present in the blood stream, also provoke well-known effects in taste, and it is quite probable that the taste hallucinations associated with nervous and mental disorder have their origin in some abnormal irritation of the nerves or brain centers involved in taste. Distilled water, which is presumably as tasteless a substance as could be found, is reported as tasteless by only about 50 per cent of observers. About 25 per cent report it as having a bitter taste, while certain cases are found in which it tastes sweet, or salt, or sour, or as having some unknown taste. As the result of careful study of these facts, Brown suggests that “we may perhaps infer that the ‘taste’ of water is not, after all, a taste quality, but is due rather to the presence or absence of some tactual characteristic; the absence, perhaps, of the ‘bite’ which is associated with sweet, salt, and sour alike.” It is also possible that mechanical stimulation of the taste organs can produce true taste qualities, just as mechanical stimulation of the retina produces spots of light and the tapping of a “warm spot” may produce a faint sensation of warmth.