Harvard Psychological Studies Part 74

Of the value of reaction-time studies, one may well believe that it lies chiefly in the way of approach which they open to the understanding of the biological significance of the nervous system.

Certainly they are not important as giving us knowledge of the time of perception, cognition, or a.s.sociation, except in so far as we discover the relations of these various processes and the conditions under which they occur most satisfactorily. To determine how this or that factor in the environment influences the activities of the nervous system, and in what way system may be adjusted to system or part-process to whole, is the task of the reaction-time investigator.

The problems of reaction time naturally fall within three cla.s.ses: Those which deal with (1) nerve transmission rates; (2) the time relations of the spinal center activities, and (3) brain processes.

Within each of these groups there are innumerable special problems for the comparative physiologist or psychologist. Under cla.s.s 1, for instance, there is the determining of the rates of impulse transmission in the sensory and the motor nerves, (_a_) for a variety of stimuli, (_b_) for different strengths of each stimulus, (_c_) for different conditions of temperature, moisture, nourishment, fatigue, etc., in case of each stimulus, (_d_) and all this for hundreds of representative animals. From this it is clear that lines of work are not lacking.

Closely related to these problems of rate of transmission are certain fundamental problems concerning the nature of the nerve impulse or wave. Whether there is a nerve wave, the reaction-time worker has as favorable an opportunity to determine as anyone, and we have a right to expect him to do something along this line. The relations of the form of the nerve impulse to the rhythm of vital action, to fatigue and to inhibition are awaiting investigation. Some of the most important unsettled points of psychology depend upon those aspects of neural activities which we ordinarily refer to as phenomena of inhibition, and which the psychologist is helpless to explain so long as the physiological basis and conditions are not known.

Then, too, in the study of animals the relation of reaction time to instincts, habits, and the surroundings of the subject are to be noted. Variability and adaptability offer chances for extended biological inquiries; and it is from just such investigations as these that biology has reason to expect much. The development of activity, the relation of reflex action to instinctive, of impulsive to volitional, and the value of all to the organism, should be made clear by reaction-time study. Such are a few of the broad lines of inquiry which are before the comparative student of animal reaction time. It is useless to dwell upon the possibilities and difficulties of the work, they will be recognized by all who are familiar with the results of human studies.

In the study of the time relations of neural processes Helmholtz was the pioneer. By him, in 1850, the rate of transmission of the nerve impulse in the sciatic nerve of the frog was found to be about 27 meters per second[4]. Later Exner[5] studied the time occupied by various processes in the nervous system of the frog by stimulating the exposed brain in different regions and noting the time which intervened before a contraction of the gastrocnemius in each case.

Further investigation of the frog's reflex reaction time has been made by Wundt[6], Krawzoff and Langendorff[7], Wilson[8] and others, but in no case has the method of study been that of the psychologist. Most of the work has been done by physiologists who relied upon vivisectional methods. The general physiology of the nervous system of the frog has been very thoroughly worked up and the papers of Sanders-Ezn[9], Goltz[10] Steiner[11] Schrader[12] and Merzbacher[13],[14] furnish an excellent basis for the interpretation of the results of the reaction-time studies.

[4] Helmholtz, H.: 'Vorlaufiger Bericht uber die Portpflanzungsgeschwindigkeit der Nervenreizung.' _Arch. f.

a.n.a.l. u. Physiol._, 1850, S. 71-73.

[5] Exner, S.: 'Experimentelle Untersuchung der einfachsten psychischen Processe.' _Pfluger's Arch._, Bd. 8. 1874, S.

526-537.

[6] Wundt, W.: 'Untersuchungen zur Mechanik der Nerven und Nervencentren.' Stuttgart, 1876.

[7] Krawzoff, L., und Langendorff, O.: 'Zur elektrischen Reizung des Froschgehirns.' _Arch. f. a.n.a.l. u. Physiol._, Physiol. Abth., 1879, S. 90-94.

[8] Wilson, W.H.: 'Note on the Time Relations of Stimulation of the Optic Lobes of the Frog.'_Jour. of Physiol._, Vol. XI., 1890, pp. 504-508.

[9] Sanders-Ezn: 'Vorarbeit fur die Erforschung des Reflexmechanismus in Lendentmark des Frosches.' _Berichte uber die Verhandlungen der Kgl. sachs. Gesellsch. d. Wissensch. zu Leipzig_, 1867, S. 3.

[10] Goltz, F.: 'Beitrage zur Lehre von den Functionen der Nervencentren des Frosches.' Berlin, 1869, 130 S.

[11] Steiner, J.: 'Untersuchungen uber die Physiologie des Froschhirns.' Braunschweig, 1885, 127 S.

[12] Schrader, M.G.: 'Zur Physiologie des Froschgehirns.'

_Pfluger's Arch._, Bd. 41, 1887, S. 75-90.

[13] Merzbacher, L.: 'Ueber die Beziebungen der Sinnesorgane zu den Reflexbewegungen des Frosches.' _Pfluger's Arch._, Bd. 81, 1900, S. 223-262.

[14] Merzbacher, L.: 'Untersuchungen uber die Regulation der Bewegungen der Wirbelthiere. I. Beobachtungen an Froschen.'

_Pfluger's Arch._, Bd. 88, 1901, S. 453-474, 11 Text-figuren.

In the present investigation it has been my purpose to study the reactions of the normal frog by the reaction-time methods of the psychologist. Hitherto the amount of work done, the extent of movements or some other change has been taken as a measure of the influence of a stimulus. My problem is, What are the time relations of all these reactions? With this problem in mind I enter upon the following program: (1) Determination of reaction time to electrical stimuli: (_a_) qualitative, (_b_) quant.i.tative, (_c_) for different strengths of current; (2) Determination of reaction time to tactual stimuli (with the same variations); (3) Auditory: (_a_) qualitative, (_b_) quant.i.tative, with studies on the sense of hearing; (4) Visual: (_a_) qualitative, (_b_) quant.i.tative, with observations concerning the importance of this sense in the life of the frog, and (5) Olfactory: (_a_) qualitative, (_b_) quant.i.tative.

The present paper presents in rather bare form the results thus far obtained on electrical, tactual, and auditory reaction time; discussion of them will be deferred until a comparison of the results for the five kinds of stimuli can be given.

V. METHOD OF STUDY.

The measurements of reaction time herein considered were made with the Hipp Chronoscope. Cattell's 'Falling Screen' or 'Gravity Chronoscope'

was used as a control for the Hipp. The Gravity Chronoscope consists of a heavy metal plate which slides easily between two vertical posts, with electrical connections so arranged that the plate, when released from the magnet at the top of the apparatus, in its fall, at a certain point breaks an electric circuit and at another point further down makes the same circuit. The rate of fall of the plate is so nearly constant that this instrument furnishes an accurate standard time with which Hipp readings may be compared, and in accordance with which the Hipp may be regulated. For, since the rate of a chronoscope varies with the strength of the current in use, with the variations in temperature and with the positions of the springs on the magnetic bar, it is always necessary to have some standard for corrections. In these experiments the time of fall of the gravity chronoscope plate, as determined by the graphic method with a 500 S.V. electric tuning fork, was 125[sigma] (_i.e._, thousandths of a second).

This period, 125[sigma], was taken as a standard, and each hour, before the beginning of reaction-time experiments, the time of the plate's fall was measured ten times with the Hipp, and for any variation of the average thus obtained from 125[sigma], the standard, the necessary corrections were made by changing the position of the chronoscope springs or the strength of the current.

The standard of comparison, 125[sigma], is shorter than most of the reaction times recorded, but since the time measured was always that from the breaking to the making of the circuit pa.s.sing through the chronoscope it cannot be urged that there were errors resulting from the difference of magnetization which was caused by variations in the reaction time. But it is evident that the danger from differences in magnetization, if such exists, is not avoided in this way; instead, it is transferred from the reaction time proper to the period of preparation immediately preceding the reaction; for, from the moment the chronoscope is started until the stimulus is given a current is necessarily pa.s.sing through the instrument. At a verbal signal from the operator the a.s.sistant started the chronoscope; the stimulus was then given by the operator, and the instrument recorded the time from the breaking of the circuit, effected by the stimulating apparatus, to the making of the circuit by the reaction of the animal. Despite precautions to prevent it, the period from the starting of the chronoscope to the giving of the stimulus was variable, and errors were antic.i.p.ated, but a number of the tests proved that variations of even a second did not cause any considerable error.

A fairly constant current for the chronoscope was supplied by a six-cell 'gravity battery' in connection with two storage cells, _GB_ (Fig. 6). This current could be used for two hours at a time without any objectionable diminution in its strength. The introduction of resistance by means of the rheostat, _R_, was frequently a convenient method of correcting the chronoscope.

[Ill.u.s.tration: FIG. 6. General Plan of Apparatus in Diagram. _H_, Hipp Chronoscope; _R_, rheostat; _C_, commutator; _SC_, storage cells; _GB_, 'Excello' gravity battery; _F_, Cattell's falling screen; _T_, reaction table; _RK_, reaction key; _SK_, Stimulating apparatus; _K_, key in chronoscope circuit; _S_, stimulus circuit.]

Fig. 6 represents the general plan of the apparatus used in these experiments.

The general method of experimentation is in outline as follows:

1. At a 'ready' signal from the operator the a.s.sistant makes the chronoscope circuit by closing a key, _K_ (Fig. 6), and then immediately starts the chronoscope.

2. Stimulus is given by the operator as soon as the chronoscope is started, and by this act the chronoscope circuit is broken and the record begun.

3. Animal reacts and by its movements turns a key, _RK_ (Fig. 6), thus making the chronoscope circuit and stopping the record.

4. a.s.sistant stops chronoscope and takes reading.

[Ill.u.s.tration: FIG. 7. Reaction Key. _l_, lever swung on pivot; _p, p_, posts for contacts with platinum plates on base; _b_, upright bar for string; _s_, spring for clamping string; _w_, wheel to carry string; _c, c_, chronoscope circuit; 1 and 2, points which are brought into contact by animal's reaction.]

The steps of this process and the parts of the apparatus concerned in each may be clearly conceived by reference to the diagram given in Fig. 6. The various forms of stimulating apparatus used and the modification of the method will be described in the sections dealing with results. The same reaction key was used throughout (see Fig. 7).

Its essential features are a lever _l_, pivoted in the middle and bearing a post at either end, _p, p_. From the middle of this lever there projected upward a small metal bar, _b_, through the upper part of which a string to the animal ran freely except when it was clamped by the spring, _s_. This string, which was attached to the subject's leg by means of a light elastic band, after pa.s.sing through the bar ran over a wheel, _w_, and hung tense by reason of a five-gram weight attached to the end. Until everything was in readiness for an experiment the string was left free to move through the bar so that movement of the animal was not hindered, but the instant before the ready-signal was given it was clamped by pressure on _s_. The diagram shows the apparatus arranged for a reaction. The current is broken, since 1 and 2 are not in contact, but a slight movement of the animal turns the lever enough to bring 1 against 2, thus making the circuit and stopping the chronoscope. When the motor reaction of the subject was violent the string pulled out of the clamp so that the animal was free from resistance, except such as the string and weight offered.

The five-gram weight served to give a constant tension and thus avoided the danger of error from this source. Between experiments the weight was placed on the table in order that there might be no strain upon the subject.

That the subject might be brought into a favorable position for an experiment without being touched by the operator a special reaction box was devised.

The animals used in these studies were specimens of _Rana clamitans_ which were kept in a tank in the laboratory throughout the year.

VI. ELECTRIC REACTION TIME.

The reaction time to electrical stimuli was determined first because it seemed probable that this form of the pain reaction would be most useful for comparison with the auditory, visual, olfactory and tactual reactions. In this paper only the electrical and the tactual reaction times will be considered. The former will be divided into two groups: (1) Those resulting from a stimulus given by touching electrodes to the leg of the frog, and (2) those gotten by having the frog resting upon wires through which a current could be pa.s.sed at any time.

_Group 1 of the electrical reactions_ were taken under the following conditions. A reaction box about 40 cm. in diameter was used. The mean temperature of the experimenting room was about 20 C. In all cases the string was attached to the left hind leg of the frog, and the stimulus applied to the middle of the gastrocnemius muscle of the right hind leg. Reaction times were taken in series of ten, excluding those which were imperfect. As the moistness of the skin affects the strength of the electric stimulus received, it was necessary to moisten the animal occasionally, but as it did not seem advisable to disturb it after each experiment this was done at intervals of five minutes throughout the series. Were it not for this precaution it might be said that lengthening of the reaction times toward the end of a series simply indicated the weakening of the stimulus which resulted from the gradual drying of the skin. The stimulus in this group was applied by means of the stimulating apparatus of Fig. 6. It is merely two wire electrodes which could be placed upon the animal, with the additional device of a key for the breaking of the chronoscope circuit the instant the stimulus was given. The most serious objection to this method of stimulating is that there is a tactual as well as an electrical stimulus.

Before presenting averages, two representative series of reactions may be considered.

SERIES I. FROG B. APRIL 9, 1900. 10 A.M.

Temperature 19 C. String to left hind leg. Stimulus to right hind leg.

Strength of stimulating current 1.0 volt, .0001 ampere.

Number of Experiment. Hour. Reaction Time. Remarks.