Most authorities appear to regard the orgastic sensations, in both sexes, as distinct and unique. It is, however, as difficult in their case as it is in those of hunger and nausea to say whether we are in presence of a novel quality or simply of a specific resultant of muscular and glandular activity. Since the sensations may ap- pear after extirpation of testes and ovaries, the latter view would seem to be the more probable.
Sexual ajanlepnia is made up, for the most part, of muscular sen- sations. It is a general sense, either of lightness and relief, or of lassitude and faintness, very like that which follows urination and defalcation: indeed, we may suppose that this resemblance is 1 A. Bain, The Senses and the hitellect, 1868, 244.
References for Further Reading 193 mainly responsible for the evacuation theory of sexual sensation at large.
The sensations attending menstruation and parturition are those of muscular pressure, pain and strain, and sometimes of nausea; neither among them nor in the following analeptic states are new qualities found.
References for Further Reading §§ 56-59. C. S. Sherrington, Common Sensation, in Schafer's Text- book, ii., 1900, 965 fF.; H. Ellis, Studies in the Psychology of Sex, iv., 1903, 1 ff. (Analysis of the Sexual Impulse); E. Meumann, Zur PVage der Sensibilitat der inneren Organe, in Archiv fur die gesamrnte Psy- chologies ix., 1907, 26 fF.
§ 56. Recent discussion makes it clear that the effect of a local an- aesthesia is more extended than the surgeons at first supposed, so that certain of the arguments upon which the conclusions of this section are based must be regarded as invalid. The evidence is at present conflict- ing, and the discrepancies cannot be referred certainly either to indi- vidual differences of sensitivity or to differences in the technique of operations. The reader may consult E. Becher, Ueber die Sensibilitat der inneren Organe, in Zeits. f. Psych., xlix., 1908, 341 fF.; Einige Be' merkungen liber die Sensibilitat der inneren Organe, in Arch. f. d. ges. Psych., xv., 1909, 356 fF.; E. Meumann, IVeiteres si/r Frage d. Sensi- bilitat d. inneren Organe u. d. Bedentung d. Organonpftndungen, ibid., o SYNAESTHESIA o SYNAESTHESIA § 60. Synaesthesia. — Every sensory stimulus of moderate intensity arouses a wide-spread reaction. It has been shown, for instance, that the sounding of a single note upon the harmonium will not only bring about an adjust- ment of the organs of hearing, but will also call out visual, verbal and other associations, often of considerable vivid- ness and detail, as well as organic sets and attitudes of various kinds. Such a result is, perhaps, only natural, in view of the manifold connections within the nervous sys- tem,— though it comes as something of a surprise to those who are accustomed to look only at the local effects of stimulation.
Quite apart, however, from this general disturbance of the organism, it not infrequently happens that a stimulus sets up, besides its appropriate sensation, a secondary or concomitant sensation. The phenomena of synaesthesia, as it is called, are scattered over the whole range of sen- sation, and are extremely varied in nature. Sometimes they seem to depend upon a purely individual feature of nervous constitution, as when a sour taste makes the scalp itch; sometimes they are common to a large number of persons: most of us shudder and grit the teeth when we hear the squeak of chalk against the blackboard, or the grating sound of a saw upon metal. The connection may obtain between separate sense-departments, as sound and sight, or between different areas of a single sense-depart- ment; thus, an itching of the nose often comes along with pricking sensations at the back of the neck on the same side, and the emptying of bladder or rectum is accompanied by a muscular shiver. In some cases, the concomitance is stable, in others it is highly variable; in some it is limited, as it were incidental, in others systematic, extending to an entire series of qualities.
The commonest form of systematic synaesthesia, known as coloured hearing, occurs almost as frequently as par- tial colour-blindness. In it, any auditory stimulus, noise, tone or sound complex, may arouse a photism or chroma- tism, a visual image of light or colour. No general rules can be laid down, since the associations vary for different persons and, within limits, may vary for the same person at different times. Two types, however, have been dis- tinguished. In the one, the connection is direct; the sound calls up the sight without any intermediary; in the other it is indirect, by way of organic sensations.
The following case may be quoted in illustration. " The vowels of the English language always appear to me, when I think of them, as possessing certain colours. Consonants, when thought of by themselves, are of a purplish black; but when I think of a whole word, the colour of the consonants tends towards the colour of the vowels. For example, in the word ' Tuesday,' when I think of each letter separately, the consonants are purplish-black, u is a light dove colour, e is a pale emerald green, and a is yellow; but when I think of the whole word together, the first part is a light grey-green, and the latter part yellow. Each word is a dis- tinct whole. I have always associated the same colours with the same letters, and no effort will change the colour of one letter, transferring it to another." ' In rare cases, colours accompany the sensations of taste and 1 From a letter cited by F. Galton, Inquiries into Human Faculty and its Development, 1883, 149.
196 Synaesthesia smell. Salt, for instance, is given by one observer as dull red, bitter as brown, sour as green or greenish blue, and sweet as a clear, bright blue. Colour concomitants of pain, pressure and temperature have also been recorded: thus, the plunging of the hands into cold water may be seen as bright red.
The synaesthetically aroused colours do not follow the lines of what we should suppose to be the least associative resistance. It is odd to read that " the word ' red ' assumes a light-green tint, while the word ' yellow ' is light-green at the beginning and red at the end." And while the observer just mentioned sees the taste of meat as red and brown, and that of bananas as yellow, he tastes Graham bread as a rich red, and all ice creams — except choco- late and coffee, which are brown because they have a bitter com- ponent— as blue.
Tonal vision, the systematic opposite of coloured hearing, seems not to occur. Incidental colour-phonisms have, however, been noted: in one case all the blues, bright as well as dark, are heard as deep and dull, and all the yellows as more or less high and ringing tones. Phonisms of pain, pressure and temperature are also known to exist. Recently, a case of gustatory (or rather gustatory-tactual) audition has been discovered; the sound of ' intelligence,' for example, tastes like raw sliced tomato, and the sound of ' interest ' like stewed tomato!
It is clear that we cannot explain coloured hearing as we explain the shudder set up by a shrill or grating noise. The colours are presented to the mind's eye; they are, as we have said, images, not peripherally excited sensations. Nevertheless, several lines of evidence go to show that they belong to the domain of sensation rather than to that of the association of ideas. First, the concomitance of colour-image and sound is, in many cases, far too detailed and too persistent to be referred to association, in the ordi- nary sense of that word. It is impossible that the con- nections should have been established during childhood; it is impossible, had they been thus established, that they should continue unchanged. Further, attempts have been made, by trained and interested observers, to trace back their synaesthetic experiences to associations formed in child- hood; but in spite of all efforts they have ended in failure. Again, we should expect that an association due to expe- rience would show, along with a certain measure of varia- tion, an underlying agreement or correspondence; whereas, as Galton remarks, " no two people agree, or hardly ever do so, as to the colour they associate with the same sound." And lastly, coloured hearing is an hereditary trait; it tends strongly to run in families. While, then, it is possible, and even probable, that synaesthesia of the incidental type may be the legacy of some vivid or thrilling experience in early life, we are forced to the conclusion that, in general, it represents a congenital endowment. As to its physical basis, we can merely guess. It may depend upon some abnor- mal disposition of the paths of connection within the brain. Or possibly it may depend, as a recent writer has sug- gested, upon an unusual elasticity of the walls of the cer- ebral arteries. On this view, a rush of blood to the audi- tory centre might, owing to the extensibility of the arteries, be propagated to the visual centre; the hearing would be coloured. The theory accounts for the loss or reduction of synaesthesia as we pass from childhood to mature life, and for its occurrence in moments of emotional stress. As the arterial structure might be a matter either of inheritance or of individual peculiarity, it allows further for both the con- genital and the acquired types of synaesthesia.
§ 61. The Image. — The facts of synaesthesia lead up to the question of the nature of the image, and of its dif- 1 98 SynaestJiesia ferences from sensation. It is usually said that the image differs from the corresponding sensation in three respects: itsajiajjtiesare relative]^_pale, faded, washed out, misty; and its intensity and duration are markedly less.
Since these differences are all differences of degree, and not of kind, it should be possible to find experimental con- ditions under which the sensation and the image are confused. Experiments have, in fact, been made, and with positive result, in the fields of sight, sound and touch.
If, for instance, the observer is seated in a well-lighted room facing a sheet of ground glass, behind which is a screened projec- tion lantern, it is often impossible for him to decide whether the faint colours that he sees on the glass are due to the lantern or to his own imagination. You say to him: Imagine that there is a picture of a banana on the glass! — and in many cases it makes no difference at all whether you show a strip of very faint yellow light from the lantern or whether you shut off the objective light altogether. The strip of seen yellow is confused with a yellow image. The experimenter, who regulates the courseof the obser- vations by signalling to a third person when the lantern is to be turned on, is sometimes greatly surprised at the gross errors made by the observer. What seems to him obviously sensory may be reported, without hesitation, as imaginative.
Again, we are frequently in doubt, in everyday life, whether we hear a particular sound or merely imagine it. And if, in the laboratory, the observer is required to listen intently to a contin- uous faint noise, such as is produced by the falling of a stream of fine sand (§ 81), the same confusion will be noted. The experi- menter may reduce the stream to a mere trickle, and may finally stop it; the observer will still, in many cases, believe that he hears the hiss.
Lastly, a similar confusion is found in experiments upon pres- sure and tickling. If, for example, in the course of a series of stimulations of a pressure spot, the experimenter says Now! but omits to touch the skin, the observer may, nevertheless, report the arousal of a pressure sensation.
It has been found, further, that a visually minded ob- server, who knows nothing of the laws of the negative after-image, may describe — and describe in correct terms — the after-images of merely imagined colours. It is also a matter of common knowledge that, in certain patho- logical states, the image may become what is called an hallucination, that is, may take on all the characters of clear and intensive sensation..
How is it, then, that we so rarely confuse image with sensation in our everyday experience? Well, the confusion may not be so uncommon as we suppose. However, if it is, the distinction may be accounted for, at any rate in large measure, by the differences of conscious context or setting in which the two processes appear. Images, for in- stance, seem to be less sharply localised than sensations; they change and shift more rapidly, and in a meaningless way; they move with movement of the eyes. But the writer is not sure that the image does not, as a rule, evince a sort of textural difference from sensation; that it is not more filmy, more transparent, more vaporous. If this is the case, then it is better to consider sensation and image as sub-classes of a particular type of mental element than to include them outright in a single class (§ 10).
Individual minds differ widely in the nature and frequency of their characteristic image-processes. Visual and auditory images are of common occurrence, although the auditory image appears, in general, to be connected with actual innervation of the larynx, that is, with kinaesthesis. Kinaesthetic images are extremely difficult to distinguish from kinaesthetic sensations. The differ- ence, in the writer's experience, is largely a matter of complexity: / 200 Symaesthesia the mental nod which gives assent to an argument is more sche- matic, involves fewer muscles and involves them less solidly, than an actual nod. Images of taste and smell have often been reported, but only exceptionally play any considerable part in consciousness. Organic images are rare.
References for Further Reading §§ 60, 61. E. Bleuler and K. Lehmann, Zwangsmiissige Lichtemp- findungen durch Schall und verwandte Erscheinungen auf dem Gebiete der anderen Sinnesempfndungen, 1881; F. Galton. Inquiries into Hu- man Facidty and its Development, 1883; G. M. Whipple, Two Cases of Synaesthesia, in American Journal of Psychology, xi., 1900, 377; J. E. Downey, An Experiment on getting an After-image from a Mental Image, in Psychological Review, viii., 1901, 42; O. Kiilpe, Ueber die Objectivirung und Subjectivirung von Sinneseindr'ucken, in Wundt's Philosophische Studien, xix., 1902, 508; R. Wallaschek, Psychologic und Pathologie der Vorstellung, 1905, 149; A. H. Pierce, A Hitherto Unde- scribed Variety of Synaesthesia, in American Journal of Psychology, xviii., 1907, 341; C.W. Perky, An Experimental Study of Imagination, THE INTENSITY OF SENSATION §62. The Intensity of Sensation. — All sensations have the attribute of intensity. A light may be bright or dull, a tone loud or faint, a pressure heavy or light, a taste strong or weak. If we take any given sensation as a starting point, we can travel from it in a straight line either towards zero, the point of its disappearance, or towards a maxi- mum, the point of its greatest possible strength (§ 12).
The intensities that lie in order along this line are, in their way, as individual as are the qualities that lie, for in- stance, along any straight line of the colour pyramid. A loud tone is not a sum of two or three weak tones, but something entirely different from a weak tone. It may be reduced to a weak tone, if we move from high to low upon the intensive scale, just as a red may be reduced to pink if we move from red towards white; but it no more contains a number of weak tones than pink contains white. In other words, intensity of sensation must not be confused with intensity of stimulus. If we want to use a weight of 5 eg. in a balance, it makes no difference whether we take a single weight of 5 eg., or two of 2 and one of 1 eg., or five of 1 eg. If we want a light of 16 c. p. at a corner of a room, it makes no difference whether we take a single 16 c. p. bulb, or two of 8, or four of 4 c. p. Stimuli can be added, subtracted, multiplied; the greater, stronger stimulus contains or sums up a certain number of lesser, weaker stimuli of the same kind. It is otherwise with sensation.
202 The Intensity of Sensation You cannot get the heavy by adding together, mentally, a number of light, or the bright by adding together a num- ber of dull: you cannot say that the heavy differs from the light by a certain fraction of the heavy or multiple of the light, or the bright from the dull by a certain fraction of the bright or multiple of the dull. Every intensity of sensation is itself, individual and characteristic: the inten- sive sensations represent, as we have said, points or posi- tions upon an intensive scale which runs from a lower limiting value to a maximum, just precisely as a particular pink or olive represents a point within or upon the colour pyramid.
We live so habitually in a world of objects, and we think so habitu- ally in terms of common sense, that it is difficult for us to take up the psychological standpoint towards intensity of sensation, and to look at consciousness as it is, apart from any objective reference. This book, we say, is heavier than that; this lamp gives the better illumination of the two; this piano has a louder tone than the others. Strictly interpreted, such statements may mean either one of two things. They may be taken physically, to mean that the books weigh differently in the balance, the lamps measure differently in c. p., the piano strings set up air-waves of different amplitude; or they may be taken psychologically, to mean that the books feel heavy and light, the lamps look bright and dull, the piano tones sound louder and less loud. As a rule, however, we are talking neither physics nor psychology, but a confused mixture of the two. It is true, of course, that we gauge the weight by lifting, the illumi- nation by eye, and the strength of tone by ear. But, in doing this, we transfer to sensation the properties that really belong to stimulus: we think of the ' feel ' of the heavier book as the ' feel ' of the lighter with some more ' feel ' added to it; we take the look of the bright lamp to be the same thing as the look of the dull, only with an addition; we regard the sound of the loud instrument as identical with the sound of the weaker, only that there is more § 62. The Intensity of Sensation 203 of it. In other words, we make the intensive sensation a copy of the intensive stimulus, and we assume that the strong sensation is built up by adding to the weak, and the weak produced by sub- tracting from the strong.
This fallacy of common sense is easily exposed by experiment. Take two glasses of sugared water, the one moderately sweet, the other very sweet, syrupy. Taste them in turn. Introspection de- clares at once that the tastes lie in the same straight line; the sweets are intensive variations of the same quality. But there is no hint — if you think only of the tastes themselves, and forget about the sugar — that the strong sweet contains the weak, is the sum of a number of weak. And it is impossible to imagine a third sweet which, if added to the weak, shall give the strong: the adding of sensation to sensation is meaningless, a task that you cannot lay hold of. The strong sweet lies fairly high up, the moderate sweet somewhat lower down, on the scale of sweet intensities. That is all.
Let us carry the experiment a little farther. Take, besides the two cups of sugared water, which we will call a and b, a number of others; make them all different, but let them all be sweeter than the moderately sweet a and less sweet than the syrupy b. Set the cups out upon a table, a and b to your left and right respec- tively, and the rest grouped at haphazard in the middle. Now try to pick out, by taste, a sweet c which lies for sensation midway be- tween a and b: taste first a, then a cup from the middle group, and then b; and keep on tasting until you are satisfied. If you take your time, and rinse the mouth between observations, so that the tongue is not cloyed, the task is rather surprisingly easy, — and the result is illuminating. For it means that we can measure off distances along the straight line which includes all the intensities of sweet; we can say by taste that the distance ac is equal to the distance cb, precisely as we can judge by eye that two spaces be- tween the pictures on the wall are equal. Nothing could show more clearly that the intensive sensation is simply a point or posi- tion upon an intensive scale; and no experience could refute more decisively the common-sense notion that it is a copy of the intensive stimulus.
204 The Intensity of Sensation Within wide limits, the intensity of sensation may be treated as an independent variable: that is to say, we may discuss it without regard to quality, and may assume that it varies while quality remains unchanged. Nevertheless, it is important that the limits be recognised. We find, on the one hand, qualities that are intrinsically weak or strong; and we find, on the other hand, intensities that are bound up with definite qualities. In these cases, the two attributes must be considered together.
We noted in § 24 that high tones are intrinsically loud and low tones intrinsically weak. The lowest tones remain faint, even when the energy of stimulus is, relatively, very considerable; and high tones give the impression of loudness, even when their stimuli are little more than liminal. So, in the sense of taste, bitter is an intrinsically strong sensation, as compared with sour, sweet and salt. Conversely, there are many scents (violet, tea, vanilla) that are intrinsically weak: they are easy to detect, they are insistent (§ 12), but they are never strong as asafoetida or musk is strong.
Again, we have seen that intensive variation of punctiform pressure stimulus gives the qualitative series contact, pressure, granular pressure (§ 39), and of punctiform pain stimulus the series itch, prick, pain (§ 41); while the dragging sensation from the muscles and the sensation of tendinous strain both alike pass over, at high intensities, into dull pain (§§ 45, 46). The most striking instance of the connection of particular intensities with definite qualities is, however, afforded by visual sensation. A change in the intensity of visual stimulus not only renders the sensation brighter or duller (intensity), but also makes it lighter or darker (quality), and in the case of colour may change all three of the constituent attributes, hue, tint and chroma (§ 16). Some psychologists have argued from this that visual sensa tions do not possess the attribute of intensity at all; that bright ness and lightness, dullness and darkness are simply different § 62. The Intensity of Sensation 205 names for the same qualitative characters.1 Such a conclusion is, however, neither probable in itself nor supported by visual theory.
We saw in § 22 that the retinal processes which arouse the sen- sations of Bk and IV are antagonistic and incompatible. If, then, a Bk and a JFfall at the same time upon the same area of the retina, any one of three things may happen: the resulting processes may be equal in intensity as well as opposite in direction, and the retina may be undisturbed; or the Bk may be the stronger stimu- lus, and may set up a Z?£-process of the intensity of Bk — W; or the IV may be the stronger stimulus, and may set up a ^-process of the intensity IV— Bk. In other words, a purely retinal vision would give us various intensities of Bk and W, but no sensations of grey. These relations are, however, complicated by the exist- ence of the sensation of neutral grey, a cortical sensation of con- stant quality; and it is the addition of neutral grey to the retinal intensities of Bk and W that makes every change in the black- white series, as we actually have it, a change of quality as well as of intensity. A retinal Bk, of whatever intensity, must darken the cortical grey; a retinal W must lighten it: and darkening and lightening are shifts of quality. To secure intensive varia- tion, with constancy of quality, we should have to increase the energy of the Bk and W components of the cortical grey, both together, in equal measure; but this is the very thing that the constitution of the retina forbids.2 — In fine, then, intensity is an 1 F. Hillebrand, Ueber die specifische Helligkeit der Farben, in Sitzungs- berichte der kais. Akademie der IVissenchaften in IVien, Mathem.-naturw. Classe, xcviii., Abth. iii., February, 1889, 88 f.; O. Kuelpe, Outlines of Psy- 2 This explanation is due to G. E. Mueller: see Zur Psychophysik der Ge- sichtsempfindungen, in Zeitschrift f. Psychologie u. Physiologie d, Sinnesorgane, x., 1896, 31 ff.; xiv., 1897, 60 ff. — We have to solve this problem of intensity for our own visual system; and our visual system is based upon the principle of antagonism. But it is quite possible that other eyes are built upon a different plan. It is possible, for instance, to think of a primitive eye, whose sensations should one and all be sensations of light (as opposed to sensations of dark) and should show a 206 The Intensity of Sensation attribute of visual as it is of all other sensations; only, the dual na- ture, peripheral and central, of the visual apparatus brings it about that intensive change of a sensation of light necessarily involves transition to another quality. When this fact is taken into account along with the facts of § 16, the qualitative changes due to change of intensity in the sphere of colour (hue, tint and chroma) follow of themselves. — So far, we have been considering cases in which the attributes of quality and intensity are interdependent. There are, further, many instances in which we cannot vary intensity without change of quality, merely because we cannot control the stimuli. For instance, it is impossible, except in the higher regions of the tonal scale, to produce a sensibly simple tone that is at all loud. If we take a flue pipe or a bottle, we find that increase of air-pressure sends the tone up; if we take a tuning-fork, we find that a violent blow introduces complicating noises and overtones. Again, noth- ing might seem easier than to secure a graded series of intensities of noise; all that we have to do is to let a ball drop from different heights upon a wooden plate. Experiment shows, however, that change in the height of fall is very likely to bring with it a change in the pitch, as well as in the loudness of the noise; it is, as a matter of fact, difficult to maintain a constant quality of noise even within the comparatively short range of intensities required for laboratory work. Once more, the quality of what we have called resultant odours (§ 32) seldom remains stable over any wide ex- tent of the intensive scale. It seems that the component stimuli behave differently, gain or lose in power to make themselves sensed, at different intensities; though in a field where so little is known it is hazardous to risk an explanation.