Sixteen Experimental Investigations from the Harvard Psychological Laboratory by Hugo Münsterberg (100 books to read .txt) 📕

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 passing through the instrument. At a verbal signal from

the operator the assistant 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 anticipated, 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.

[Illustration: 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 assistant 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. Assistant stops chronoscope and takes reading.

[Illustration: 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 passing 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 passed 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 ampère.

Number of

Experiment. Hour. Reaction Time. Remarks.

1 10.25 No reaction.

2 10.27 No reaction.

3 10.30 139[sigma]

4 10.34 164

5 10.35 102

6 10.37 169

7 10.39 151

8 10.40 152

9 10.42 144

10 10.43 152

11 10.45 122

12 10.51 179

13 10.54 No reaction.

Average of 10, 147.4[sigma]

SERIES 2. FROG F. ELECTRICAL STIMULUS.

No. Hour. Reaction Time. Remarks. Deviation from Mean.

1 10.19 35[sigma] Probable reaction

to visual stim.

2 10.22 173 4.7

3 10.24 161 - 7.3

4 10.25 133 -35.3

5 10.26 199 30.7

6 10.28 130 -38.3

7 10.32 179 10.7

8 10.34 187 18.7

9 10.35 60 Probable reflex.

10 10.37 183 14.7

11 10.38 166 - 2.3

12 10.39 172 3.7

Average of 10, 168.3[sigma] Average of first 5, 159.2[sigma]

Average Variation, 16.64[sigma] Average of second 5, 177.4[sigma]

Both are fairly representative series. They show the extremely large

variations, in the case of series 1, from 102 to 179[sigma]. In all

these experiments such variation is unavoidable because it is

impossible to have the conditions uniform. A very slight difference in

the frog’s position, which could not be detected by the operator,

might cause considerable difference in the time recorded. Efforts were

made to get uniform conditions, but the results seem to show that

there is still much to be desired in this direction.

Tables VII. contains the results of four series of ten reactions each

for frog A. It will be noticed that the time for the first five in

each series is much shorter than that for the last five; this is

probably indicative of fatigue.

TABLE VII.

REACTION TIME OF FROG A TO ELECTRICAL STIMULI.

Series of Averages Averages of Averages of

ten reactions. of series. first five. second five.

1 163.1[sigma] 134.6[sigma] 191.6[sigma]

2 186.2 176.2 196.2

3 161.1 125.2 197.0

4 158.3 101.6 215.0

General averages 167.2[sigma] 134.4[sigma] 199.9[sigma]

TABLE VIII.

REACTION TIME OF FROG B TO ELECTRICAL STIMULI.

1 132.7[sigma] 118.2[sigma] 147.4[sigma]

2 196.6 167.8 225.4

3 147.4 145.5 149.8

4 157.5 152.0 163.0

General averages 158.6[sigma] 145.9[sigma] 171.4[sigma]

TABLE IX.

NORMAL AND REFLEX REACTION TIME OF SIX ANIMALS TO ELECTRICAL STIMULUS.

Normal. Reflex.

Average for 20 Average for 20

Frog. reactions. Mean Var. reactions. Mean Var.

A 149.5[sigma] 24.0[sigma]

B 158.3 16.0 51.5[sigma] 8.0[sigma]

C 191.0 24.3

D 167.0 10.1

E 182.4 28.0 45.1 5.5

F 176.3 10.2 46.0 4.5

General

Average. 167.9[sigma] 18.8[sigma] 47.5[sigma] 6.0[sigma]

For D the average is for ten reactions.

B and E were males, F a female; the sex of the others was

not determined by dissection and is uncertain.

Early in the experiments it became evident that there were three

clearly defined types of reactions: there were a number of reactions

whose time was shorter than that of the ordinary quick voluntary pain

reaction, and there were also many whose time was considerably longer.

The first type it was thought might represent the spinal reflex

reaction time. For the purpose of determining whether the supposition

was true, at the end of the series of experiments three of the frogs

were killed and their reflex reaction time noted. This was done by

cutting the spinal cord just back of the medulla, placing the animal

on an experimenting board close to the reaction key with the thread

from the key fastened to the left leg as in case of the previous work

and stimulating the gastrocnemius with an induced current by the

application of wire electrodes.

In Table IX. the reflex reaction times for the three animals are

given.

The following results obtained with frog E show that the time of

reaction increases with the increase in the time after death. The

average of 20 reactions by E taken an hour after the cord had been

cut was 45.5[sigma]; the average of 20 taken twenty hours later was

55.85[sigma].

As a rule the reflex reactions were but slightly variable in time as

is indicated by the accompanying series.

SERIES OF REFLEX REACTIONS OF FROG F.

Taken at rate of one per minute.

1 50[sigma]

2 58

3 55

4 59

5 48

6 46

7 45

8 51

9 42

10 44

Throughout these experiments it was noticed that any stimulus might

cause (1) a twitch in the limb stimulated, or (2) a twitch followed by

a jump, or (3) a sudden jump previous to which no twitch could be

detected. And it soon appeared that these types of reaction, as it

seems proper to call them, would have to be considered in any

determination of the mean reaction time. As proof of the type theory

there is given (Fig. 8) a graphic representation of 277 reactions to

the electrical stimulus.

[Illustration: FIG 8: Distribution of