Chapter III

.

The facts I proceed to quote may also be taken as a supplement to that chapter. Wundt writes:

"When we wait with strained attention for a stimulus, it will often happen that instead of registering the stimulus, we react upon some entirely different impression,--and this not through confounding the one with the other. On the contrary, we are perfectly well aware at the moment of making the movement that we respond to the wrong stimulus. Sometimes even, though not so often, the latter may be another kind of sensation altogether,--one may, for example, in experimenting with sound, register a flash of light, produced either by accident or design. We cannot well explain these results otherwise than by assuming that the strain of the attention towards the impression we expect coexists with a preparatory innervation of the motor centre for the reaction, which innervation the slightest shock then suffices to turn into an actual discharge. This shock may be given by any chance impression, even by one to which we never intended to respond. When the preparatory innervation has once reached this pitch of intensity, the time that intervenes between the stimulus and the contraction of the muscles which react, may become vanishingly small."[350]

"The perception of an impression is facilitated when the impression is preceded by a warning which announces beforehand that it is about to occur. This case is realized whenever several stimuli follow each other at equal intervals,--when, e.g. we note pendulum movements by the eye, or pendulum-strokes by the ear. Each single stroke forms here the signal for the next, which is thus met by a fully prepared attention. The same thing happens when the stimulus to be perceived is preceded, at a certain interval, by a single warning: the time is always notably shortened.... I have made comparative observations on reaction-time with and without a warning signal. The impression to be reacted on was the sound made by the dropping of a ball on the board of the 'drop apparatus.'... In a first series no warning preceded the stroke of the ball; in the second, the noise made by the apparatus in liberating the ball served as a signal.... Here are the averages of two series of such experiments:

Height of Fall. Average. Mean Error. No. of Expts.

25 cm. {No warning 0.253 0.051 13 {Warning 0.076 0.060 17

5 cm. {No warning 0.266 0.036 14 {Warning 0.175 0.035 17

"... In a long series of experiments, (the interval between warning and stimulus remaining the same) the reaction-time grows less and less, and it is possible occasionally to reduce it to a vanishing quantity (a few thousandths of a second), to zero, or even to a negative value.[351]... The only ground that we can assign for this phenomenon is _the preparation (vorbereitende Spannung) of the attention_. It is easy to understand that the reaction-time should be shortened by this means; but that it should sometimes sink to zero and even assume negative values, may appear surprising. Nevertheless this latter case is also explained by what happens in the simple reaction-time experiments" just referred to, in which, "when the strain of the attention has reached its climax, the movement we stand ready to execute escapes from the control of on will, and we register a wrong signal. In these other experiments, in which a warning foretells the moment of the stimulus, it is also plain that attention accommodates itself so exactly to the latter's reception that _no sooner is it objectively given than it is fully apperceived, and with the apperception the motor discharge coincides_."[352]

Usually, when the impression is fully anticipated, attention prepares the motor centres so completely for both stimulus and reaction that the only time lost is that of the physiological conduction downwards. But even this interval may disappear, i.e. the stimulus and reaction may become objectively contemporaneous; or more remarkable still, the reaction may be discharged before the stimulus has actually occurred.[353] Wundt, as we saw some pages back (p. 411), explains this by the effort of the mind so to react that we may feel our own movement and the signal which prompts it, both at the same instant. As the execution of the movement must precede our feeling of it, so it must also precede the stimulus, if that and our movement are to be felt at once.

The peculiar theoretic interest of these experiments lies in their _showing expectant attention and sensation to be continuous or identical processes, since they may have identical motor effects_. Although other exceptional observations show them likewise to be continuous _subjectively_, Wundt's experiments do not: he seems never, at the moment of reacting prematurely, to have been misled into the belief that the real stimulus was there.

As concentrated attention accelerates perception, so, conversely, perception of a stimulus is _retarded by anything which either baffles or distracts the attention_ with which we await it.

"If, e.g., we make reactions on a sound in such a way that weak and strong stimuli irregularly alternate so that the observer can never expect a determinate strength with any certainty, the reaction-time for _all_ the various signals is increased,--and so is the average error. I append two examples.... In Series I a strong and a weak sound alternated regularly, so that the intensity was each time known in advance. In II they came irregularly.

I. _Regular Alternation._

Average Time. Average Error. No. of Expts.

Strong sound 0.116" 0.010" 18 Weak sound 0.127" 0.012" 9

II. _Irregular Alternation._

Strong sound 0.189" 0.038" 9 Weak sound 0.298" 0.076" 15

"Still greater is the increase of the time when, unexpectedly into a series of strong impressions, a weak one is interpolated, or _vice versâ_. In this way I have seen the time of reaction upon a sound so weak as to be barely perceived rise to 0.4" or 0.5", and for a strong sound to 0 25". It is also matter of general experience that a stimulus expected in a general way, but for whose intensity attention cannot be adapted in advance, demands a longer reaction-time. In such cases ... the reason for the difference can only lie in the fact that wherever a preparation of the attention is impossible, the time of both perception and volition is prolonged. Perhaps also the conspicuously large reaction-times which are got with stimuli so faint as to be just perceptible may be explained by the attention tending always to adapt itself for something more than this minimal amount of stimulus, so that a state ensues similar to that in the case of unexpected stimuli.... Still more than by previously unknown stimuli is the reaction-time prolonged by _wholly unexpected_ impressions. This is sometimes accidentally brought about, when the observer's attention, instead of being concentrated on the coming signal, is dispersed. It can be realized purposely by suddenly thrusting into a long series of equidistant stimuli a much shorter interval which the observer does not expect. The mental effect here is like that of being startled;--often the startling is outwardly visible. The time of reaction may then easily be lengthened to one quarter of a second with strong signals, or with weak ones to a half-second. Slighter, but still very noticeable, is the retardation when the experiment is so arranged that the observer, ignorant whether the stimulus is to be an impression of light, sound, or touch, cannot keep his attention turned to any particular sense-organ in advance. One notices then at the same time a peculiar unrest, as the feeling of strain which accompanies the attention keeps vacillating between the several senses.

"Complications of another sort arise when what is registered is an impression anticipated both in point of quality and strength, but accompanied by other stimuli which make the concentration of the attention difficult. The reaction-time is here always more or less prolonged. The simplest case of the sort is where a momentary impression is registered in the midst of another, and continuous, sensorial-stimulation of considerable strength. The continuous stimulus may belong to the same sense as the stimulus to be reacted on, or to another. When it is of the same sense, the retardation it causes may be partly due to the distraction of the attention by it, but partly also to the fact that the stimulus to be reacted on stands out less strongly than if alone, and practically becomes a less intense sensation. But other factors in reality are present; for we find the reaction-time more prolonged by the concomitant stimulation when the stimulus is weak than when it is strong I made experiments in which the principal impression, or signal for reaction, was a bell-stroke whose strength could be graduated by a spring against the hammer with a movable counterpoise. Each set of observations comprised two series; in one of which the bell-stroke was registered in the ordinary way, whilst in the other a toothed wheel belonging to the chronometric apparatus made during the entire experiment a steady noise against a metal spring. In one half of the latter series (A) the bell-stroke was only moderately strong, so that the accompanying noise diminished it considerably, without, however, making it indistinguishable. In the other half (B) the bell-sound was so loud as to be heard with perfect distinctness above the noise.

Mean. Maximum. Minimum. No. of Experiments. A {Without noise 0.189 0.214 0.156 21 (Bell-stroke {With noise 0.313 0.499 0.183 16 moderate) {

B {Without noise 0.158 0.206 0.133 20 (Bell-stroke {With noise 0.203 0.295 0.140 19 loud) {

"Since, in these experiments, the sound B even with noise made a considerably stronger impression than the sound A without, we must see in the figures a direct influence of the disturbing noise on the process of reaction. This influence is freed from mixture with other factors when the momentary stimulus and the concomitant disturbance appeal to different senses. I chose, to test this, sight and hearing. The momentary signal was an induction-spark leaping from one platinum point to another against a dark background. The steady stimulation was the noise above described.

Spark. Mean. Maximum. Minimum. No. of Expts. Without noise 0.222 0.284 0.158 20 With noise 0.300 0.390 0.250 18

"When one reflects that in the experiments with one and the same sense the relative intensity of the signal is always depressed [which by itself is a retarding condition] the amount of retardation in these last observations makes it probable that _the disturbing influence upon attention is greater when the stimuli are disparate than when they belong to the same sense_. One does not, in fact, find it

## particularly hard to register immediately, when the bell rings in the

midst of the noise; but when the spark is the signal one has a feeling of being coerced, as one turns away from the noise towards it. This fact is immediately connected with other properties of our attention. The effort of the latter is accompanied by various corporeal sensations, according to the sense which is engaged. The innervation which exists during the effort of attention is therefore probably a different one for each sense-organ."[354]

Wundt then, after some theoretical remarks which we need not quote now, gives a table of retardations, as follows:

Retardation. 1. Unexpected strength of impression: _a_) Unexpectedly strong sound 0.073 _b_) Unexpectedly weak sound 0.171 2. Interference by like stimulus (sound by sound) 0.045[355] 3. Interference by unlike stimulus (light by sound) 0.078

It seems probable, from these results obtained with elementary processes of mind, that all processes, even the higher ones of reminiscence, reasoning, etc., whenever attention is concentrated upon them instead of being diffused and languid, are thereby more rapidly performed.[356]

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Still more interesting reaction-time observations have been made by Münsterberg. The reader will recollect the fact noted in