of stimulus — cannot but suggest Weber's law, the general formu- lation of which is precisely the same. The rule suggests, that is, that we compare or estimate ex- ri Jl O by the help of Yig. 5. — Illustration of Weber's Law in the sphere of the intensity of eye-measurement. The length of b stands midway, some attendant fof sensation, between the lengths of a and c. If the sensation lines are measured it will be found that a:b — b\c.
There is good reason for thinking that our estimation of visual extent is originally made by the help of the intensity of strain sensations. Each eye is slung in its socket upon six separate muscles. When we com- pare two lines, the natural thing to do is to * run the eyes along ' them; and this movement of the eyes calls forth sensations of muscular contraction and of tendinous strain. A longer line occa- sions a more severe (stronger) strain, and a shorter hne a less severe strain. We estimate extent in terms of intensity.
The numerical expression of Weber's law for strain intensities in experiments with hfted weights is one-fortieth. It is only to be expected that the fraction should be somewhat less in the case of the eye. The eye is constantly engaged with extents and their estimation, whereas the hand and arm are not so highly practised in the comparison of lifted weights. And the eyeball, with its six muscles and the tendons attaching to them, is set by itself in a bony socket, out of the reach of disturbance from the rest of the body; whereas the muscles and tendons of hand and arm interact in a much more complex way, and are liable to disturbance from shoulder, back, etc., — indeed, from all the muscles and tendons employed to maintain a particular bodily attitude.
It must not be supposed, however, that our judgment of the ex- tents of two lines in a particular experiment is necessarily based upon the intensities of strain sensations coming from the tendons of the eye muscles. The fiirther we advance into psychology, the more clearly shall we see that the mind can travel by many roads to the same result. We may ' remember ' an event in half-a- 84 Intensity, Extent, Duratioji of Sensation dozen different ways; we may 'compare' visual extents by half-a-dozen different methods. The natural and original way to compare them is, in all probabiUty, by aid of the intensity of attend- ant strain sensations; if we take this way, Weber's law will, of course, be found to govern our judgment.
Method. — Three white threads are stretched vertically over a grey background. The distance 1-2 is objectively equal to the distance 2-3. The former distance remains constant throughout the experiment. Thread 3 is now gradually moved outwards, till 2-3 seems just longer than 1-2. Owing to the error of expecta- tion (§ 24), the judgment 'longer' will come too soon, i.e., the estimation will be more accurate than the observer's average esti- mation. Thread 3 is then set further outwards, and from that point moved slowly inwards, until the tv\*o distances are apparently equal again. The judgment of equality comes too soon, i.e., is less accurate than the observer's average judgment. The exper- iment is now repeated in the reverse direction. We start out from objective equality of 1-2 and 2-3, and move 3 inwards, until 2-3 is just perceptibly shorter than 1-2. The judgment is too accurate. Then, beginning from a point further inwards, we move 3 out, until 2-3 is apparently equal to 1-2. The judgment is too inaccurate. — The whole procedure is now repeated, except that the distance 2-3 is kept constant throughout the experiments, while the distance 1-2 is varied.
The eight judgments thus obtained are averaged: and the dif- ference between the constant distance and this average gives us a measure of the subject's accuracy in the discrimination of hori- zontal extents.
§ 29. The Time Sense. — The question of this Section is similiar to those of the tv^o preceding: Is there any gen- eral law governing the relation of stimulus to sensation duration.? or, as it has more often been phrased: Is there any general law governing our estimation of time intervals.? A time interval is never an * empty ' time; if it is conscious, it is always the duration of something, some conscious process or processes. Psychologically regarded, * inter- val ' and ' duration ' are convertible terms.
Experiments upon the estimation of intervals (durations) are grouped together under the heading of the ' time sense.' It must be borne in mind that this expression is merely figurative. We have no special sense of time, any more than we have an intensity sense or an extent sense. All sensations have duration, but we have no sensation of duration.
It has been found by experiment that judgments of the relative length of intervals (durations) are of three distinct kinds, according as the intervals themselves are shorter than half-a-second, longer than three seconds, or lie be- tween these time limits.
(i) Our estimation of time intervals of less than half-a- second's duration is very accurate. We cannot as yet say with any degree of certainty upon what psychological grounds the judgment that one such interval is longer or shorter than another is based. But it is never a direct judgment of duration, i.e., a judgment based upon the estimation of two conscious durations. Hence we need not consider it here.
All that we know at present of these judgments (beyond the fact that they are not judgments of duration) is that they vary with the sense department from which the stimuli which limit the intervals are taken, with the rhythm and accent of these stimuli, and with the direction of the attention to one stimulus or another.
(i) If two equal intervals — say, of a quarter of a second's duration — are given, the one bounded by visual and the other by cutaneous (pressure) stimuli, the latter appears to be considerably the shorter of the two. This is because the visual after-sensation (§ 24) lasts longer than the cutaneous, and the ' visual ' interval is thus extended in a way in which the cutaneous interval is not.
S6 Intensity, Extent, Duration of Sensation (2) When we listen to a rapid series of taps or clicks, we find ourselves ^ forced/ as it were, to accent some more strongly than others; the sounds ' fall ' into a rhythm. Suppose that we have three taps, i.e., two intervals. If we accent the first, — i ' 2 3, — the first interval is judged to be the longer; if we accent the second, — 12' 3, — the second; if the third, — i 2 3', — the first again. The effect of accent is to lengthen the following and shorten the pre- ceding interval. If the series really increases in loudness, the inter- vals seem to grow shorter; if it decreases, they grow longer. (3) A chance direction of the attention has the same effect as accentuation or real change of intensity of the limiting stimuli. Thus it may reverse the judgment instanced under (i). There is here no direct comparison of durations; our judgment of duration depends entirely upon the power of the limiting stimuli to hold the atten- tion. — The phenomena of accent can be observed in the ticking of a watch (four or five ticks to the one second) held to the ear.
(2) Estimation of intervals longer than three seconds is an estimation of duration, but not a direct estimation. Our judgment that one interval is longer than another is based principally upon the difference in the number of mental processes which ran their course within the two total dura- tions. The more processes introspection shows to have occurred in an interval, the longer is that interval judged to be. These intervals, also, may be passed over here.
(3) Durations which lie between the limits of half-a- second and three seconds are estimated as durations. For their estimation the law holds that equal differences of conscious duration are produced by relatively equal differ- ences of stimulus duration. That is, if time a is to seem as much longer than time b as time c seems longer than time d, the proportion must hold that a — b\b\\c — d'.d.
We are again reminded of Weber's law. And indeed, just as estimation of visual extents is based upon* intensities of strain sen- §§ 29, 30. Time Sense and Meaning of Weber s Law diy sation (the sensations proceeding from the tendons of the eye muscles), and thus follows Weber's law, so apparently is the estimation of these time-intervals base^ upon intensities of strain sensation, — and the law formulated is not really a duration law, but Weber's law itself When we try to discover by introspection what means we have used for our comparison of two durations of this third kind, we find that strain intensities have played a great part in the formation of the judgment. The strain sensations come (i) from the expectant attitude of the whole body, and (2) from the adjustment of the sense-organ to the stimuli which limit the intervals to be compared. We estimate duration in terms of intensity: the more intensive the strain, the longer must the interval have been; the less the strain, the shorter the time.
Again, however, the natural and original way (§ 28) need not necessarily be followed; and hence the results of experiments upon the estimation of these ' moderate ' intervals do not always agree. Much work remains to be done, before the psychological facts upon which the different time judgments are based can be completely described.
Method. — An electric hammer is connected with an electric clock in such a way that it gives three sharp taps upon its base at the required intervals. The subject has to compare the lengths of the two intervals, just as he would compare two intensities or extents. We may employ the method of gradual change (§ 28), increasing and decreasing one interval until a difference between the two is remarked, or the method of right and wrong cases (§ 27), working with constant intervals which are very little dif- ferent.
Or we may allow the hammer to give two strokes — one dura- tion— only, and require the subject to arrest the electric clock (by pressing a key) as soon as a time has elapsed which he judges to be equal to the given time. The errors w4iich he makes in a series of experiments furnish a measure of the accuracy of his estimation of duration.
§ 30. The Meaning of Weber's Law. — We can now pro- ceed to answer the question of § 25: What goes on in the S8 Intensity, Extent, Duration of Se7isation bodily organs when a sensation changes in intensity? The psychological facts embraced under Weber's law must be brought into connection with what physiology tells us of the effect produced upon nervous substance by stimuli of different intensities.
(i) We know that nervous substance resists the incom- ing of stimulation. The resistance which it offers can be overcome only by stimuli of a certain strength. This physiological knowledge enables us to understand why very weak stimuli are not sensed at all: they are too weak to overcome the resistance which they encounter in the nervous centres.
(2) Weak stimulation makes the nervous substance more excitable; strong stimulation leaves it less excitable. Hence Weber's law does not hold for stimuli which ap- proach to minimal or maximal values. As the law holds over a wide range of stimuli, i.e., for all those of * moder- ate ' strength, we must suppose that moderate stimulation does not change the excitability of nervous substance.
(3) The fact that moderate stimulation does not alter nervous excitability, taken together with the fact that ner- vous substance resists the incoming of stimuli, accounts for the general rule that change in sensation intensity does not come with every change in the intensity of stimulus. It might be thought that, when once an excitation had been set up, the resistance of nervous substance had been once for all overcome, and that we ought, consequently, to sense any addition made to the strength of stimulus. But the moderately excited nervous substance offers as much resistance as the unexcited to the incoming stimulus; and a small addition to the strength of the latter is, therefore, not sensed.
§ 30. The Meaning of Weber's Lazv 89 (4) Physiology asserts that a stimuhis which affects a particular sense-organ not only produces an excitation within that organ, but is more or less widely diffused over the whole body. Thus a light-stimulus not only sets up an excitation within the retina, but also has an effect upon circulation, respiration, etc. Some part of the energy of every stimulus, then, is lost for sensation.
Weber's law shows that the part which is lost (and con- sequently the part which is used) always bears the same relation to the total stimulus. A light of 100 candle-power is just different from a light of lOi; a light of 200 from a light of 202. Just the same proportion of light is lost (and just the same proportion used) in the one case as in the other.
Since strong stimulation decreases the excitability of nervous substance, it is intelligible that the fraction which expresses the relative increase of stimulus necessary to produce a just notice- able increase of sensation should be larger in the case of strong stimuli than in that of moderate (Weber's law). And we find that while tlie just noticeable difference of noise is one-third for moderate sounds, it is much more than one-third for extremely loud sounds.
Since weak stimulation increases the excitabihty of nervous substance, we might suppose that the corresponding fraction would be smaller than that which expresses Weber's law. The reverse is the case: the fraction is larger for less than moderate, as it was for more than moderate stimuli. The just noticeable difference of very faint noise, that is, is also more than one- third.
The reasons for this, at first sight anomalous, fact are as follows, (i) It is difficult to hold the attention upon a very weak stimulus. Hence small differences between very faint sensations may pass un- noticed {cf. §§ T^^, 41). (2) The sense-organs are at all times subject to the action of weak internal stimulation. In some cases 90 Intensity^ Extent, Duration of Sensation this stimulation is strong enough to maintain a permanent sensation {cf. the black of the retina, § 24), in other cases it only occasion- ally reaches the necessary strength (we are ordinarily insensible, e.g., to the internal ear-noises, corresponding to the pumping of blood through the arteries of the internal ear): it is always present in some degree. When we state numerically the increase of stim- ulus required to produce an increase of sensation, we make this in- crease a fractional part of the external stimulus alone: it should properly be calculated as a fractional part of external plus internal stimulus. Thus if a very faint sound had to be increased by one- half, that the two might be sensed as different, we should say that Weber's law did not hold: Weber's law demands a difference of one-third only. Yet this addition, which is one-half of the ex- ternal sound, might be one-third of external sound plus artery- sounds, — if we could but measure the latter. In general terms, the deviation from Weber's law may oftentimes be apparent only, not real. (3) If the deviation be real, we may suppose that the increase of nervous excitability, within the time limits of a single experiment, is not sufficient to counterbalance the resistance offered by nervous substance to the incoming of stim- ulus.
(5) The numerical expression of Weber's lav^ is differ- ent in the different sense departments. By the eye we can appreciate a difference of one-hundredth in the in- tensity of a stimulus; by the ear, a difference of one-third only. This proves that the nervous substance of the eye is far more excitable by ether vibrations than is that of the ear by air-waves.
It is plain from these considerations that the bodily con- ditions of sensation intensity are of a general nature, that they are alike in all the sense-organs. And wherever our estimation of durations and extents is based upon differ- ences in the intensity of strain.sensations, the bodily con- ditions of these aspects of sensation are the same as the § 30. TJie Meaning of Weber s Lazv 91 conditions of intensity. Weber's law ' explains ' the phe- nomena of intensity, extent and duration, over the whole domain of sensation, in the sense in which our account of the structure and function of eye or ear ' explains ' the qualities of vision or audition.
CHAPTER V Affection as a Conscious Element. The Methods OF investigating Affection § 31. The Definition of Affection. — We can quite well conceive of a mind which should be entirely made up of sensation processes and the processes arising from the interconnection and intermixture of sensations (perceptions and ideas). Certain mythologies represent the divine mind to be of this type: it is omniscient {i.e., the ideas of which it consists form the total sum of all possible ideas), but it is also indifferent (unfeeling) and contem- plative (inactive). Mind as we observe it, however, is of a very different nature. The living organism is exposed through its sense-organs to all manner of stimuli, and its mental processes are in large measure the sensation pro- cesses directly aroused by these stimuli. But the organism is not indifferent. It not only senses: it feels. It not only receives impressions and has sensations: it receives impressions in a certain way.
When we have spoken in previous Sections of the effect of stimulation upon a bodily organ, we have thought of the body as entirely passive. We have pictured the stimulus as forcing its way through the organ, and setting up some change in it and in the brain, just as we might have pictured the photographer's acid eating away the surface of the sensitive plate. But the body is alive; and 92 §31- The Defiiiition of Affection 93 life means the balance of power (more or less perfect) in the perpetual conflict of two opposing forces, — growth and decay. No impression can be made upon the living body that does not tend in some way to change this balance, — that does not tip the scale on one side or the other, furthering growth or hastening decay. Hence every stimulus that produces a special effect, within a certain organ and the area of the brain cortex with which that organ is connected, must also produce a general effect upon the nervous system {cf. § 30). It must help either to build up nervous substance or to break it down. The organism is a whole: and what affects it in either of these ways at one part, must affect it as a whole, in all. The conscious processes corresponding to the general bodily processes thus set up by stimuli — processes not confined to definite bodily organs — are termed affections.
It will be readily understood that we cannot classify affections as we classified sensations; that there are no different orders or groups of affections as there are of sensations. There are many sense-organs, and each organ furnishes one or two groups or classes of sensations: but there is only one affective organ, — the whole body. It will be seen, further, that there cannot be so many quali- ties of affection as there are, e.g.y of sight or hearing. We have a large number of sensations of colour, because ether-waves of different lengths set up different chemical processes within the retina; we have a large number of sensations of tone, because air-waves of different lengths throw different fibres of the basilar membrane into vi- bration. But there are only two bodily processes to give rise to affective processes: the building-up process (anab- olism) and the breaking-down process (catabolism). We 94 Affection as a Conscious Element should expect, then, to find no more than two quaHties of affection. And introspection tells us that the expectation is correct. The anabolic bodily processes correspond to the conscious quality of pleasantness^ catabolic processes to that of unpleasantness. These are the only qualities of affection.
In our definition of sensation, we took account of its simplicity as a conscious process, and of its bodily con- ditions. Of the simplicity of affection — pleasantness and unpleasantness — there can be no doubt: neither of its two qualities can be analysed into more simple and ele- mentary components. It is, as we have seen, unlike sen- sation in that it is not connected with a bodily process in a definite bodily organ. The organism, as a whole, receives the impressions made upon it in a certain way: an affection is the conscious process arising from its /way of receiving ' a particular impression.
§ 32. Affection and Sensation. — The processes of pleas- antness and unpleasantness seem, at least in many cases, to bear a strong resemblance to certain concrete experi- ences which we have analysed, provisionally, as complexes of sensations (§ 21). Thus pleasantness may suggest health, drowsiness, bodily comfort; and unpleasantness pain, discomfort, overtiredness, etc. Hence it might be supposed — notwithstanding the statements of the preced- ing Section — that the two qualities which we have ascribed to affection are in reality two new qualities of common or organic sensation; perhaps common, like pain, to all the sensory nerves of the body, perhaps restricted, like press- ure, to a few great groups of sensory nerves.
Now there can be no doubt of the resemblance in the instances cited. But the reason of it is simply this: that § 32. Affection and Sensation 95 health, drowsiness, and bodily comfort are pleasant, i.e., that pleasantness is one of the constituent processes, run- ning alongside of various sensation processes, in the total conscious experience which we call 'health,' etc.; and that pain, bodily discomfort, and overtiredness are unpleas- ant, i.e., that unpleasantness is one of the processes con- tained in each of these complex experiences. Beyond this there is no resemblance: a sensation process is radically different from a pleasantness or unpleasantness. The following considerations will be enough to make the fact clear.
(i) The first great difference between sensations on the one hand and pleasantness and unpleasantness on the other is that the former are looked upon as more or less common property, — as inherent, so to speak, in the objects which give rise to them, and therefore as possible parts of every one's experience, — while the latter are our own peculiar property. Blue seems to belong to the sk}f; but the pleasantness of the blue is in me. Warmth seejn's to belong to the burning coals; but the pleasantness of the warmth is in me. Regarded from the point of view of the psychologist, blue, warm and pleasant are all mental processes, \ all facts of one's own experience; regarded from the point of view of ordinary life, blue and warm are somehow detachable from oneself and one's personal experience, whereas pleasantness is always within oneself. The distinction is unhesitatingly drawn in popular thought, and clearly shown in language. It points to a real differ- ence between sensation and affection as factors in mental experience, — a difference which the psychologist must make explicit in his definition of the two processes.
The same difference is observed even when we compare 96 Affection as a Conscious Element the affective processes with those sensations which are occasioned from within, by a change in the state of a bodily organ. The unpleasantness of a toothache is far more personal to me than the pain of it. The pain is ' in the tooth '; the unpleasantness is as wide as conscious- ness.^ So too when the discomfort of a cramped position makes me shift in my chair: the muscular and circulatory pains proceed from certain parts of the body, but the unpleasantness pervades the whole consciousness of the moment. Satiety and easy digestion dispose one to a favourable view of things in general: the sensations which enter into them are referred to the alimentary canal, but their pleasantness is diffused over the whole mental horizon.
We may put this first difference between sensation and affection briefly as follows: Sensations are objective and local, affections are subjective and coextensive with con- sciousness.
It is an obvious corollary to this statement that two affections cannot run their course as conscious processes at the same time. Nothing can be at once pleasant and unpleasant.
* Why, then/ it may be asked, ' do we hear of " mixed feel- ings"? Why does Shakespeare make Juliet say: "Parting is such sweet sorrow" — i.e., a pleasant unpleasantness? Or how can Tennyson's Geraint look at the dinnerless mowers with "humorous ruth" — i.e., again, with a pleasant unpleasant feel- ing? * The answer is that the nervous system may very well be exposed, at different quarters, to stimuli some of which are cata- bolic and some anabolic; some of which, that is, if felt by them- selves, would be felt pleasantly, and some of which, if felt alone, 1 The word ' pain,' as used in ordinary conversation, often means the whole toothache experience: pressure sensation, pain sensation and unpleasantness. In the text the word is used in its strict meaning, to indicate the common sen- sation in the complex (§ 21).
§ 32. Affection mid Sensation 97 would be felt unpleasantly. And the attention may oscillate, as it were, between the one group and the other; so that pleasant- ness and unpleasantness succeed each another in consciousness with great rapidity. The boy leaves home for school with ^ mixed feehngs '; he is sorry to go (unpleasantness), but his new watch partly reconciles him to his fate (pleasantness). Nevertheless, at any given moment he is either glad or sorry; watch-conscious- ness and parting-consciousness succeed each other rapidly, but never overlap; there is no moment of combined joy and sorrow.
(2) If we are exposed for a long time together to the same stimulus (and if the sensation which the stimulus arouses ds not of a kind to pass over into pain: § 25), we cease to be affected by it at all. The cookery of a foreign country is, when we first make acquaintance with it, dis- tinctly pleasant or unpleasant; but in either case quickly becomes indifferent. Dwellers in the country do not find the pleasure in country scents and odours that the towns- man does; they have 'grown used' to their surroundings. The whir of a sewing machine in the room above that in which we are working may at first be extremely annoying; but as we become accustomed to it, its unpleasantness dis- appears. The smell of the dissecting room, which sickens us at our first entry, does not affect us at all after a little time. And it is the same with centrally aroused pleasant- ness and unpleasantness \cf. (4) below]. During the first few weeks of our stay in a beautiful neighbourhood we may be continually delighted with the colours and forms of the landscape. But we soon grow indifferent to them: fields and streams and hills are seen as clearly as ever, but have ceased to excite pleasure. The beauty of a new dinner service may be remarked on with pleasure for a