Sixteen Experimental Investigations from the Harvard Psychological Laboratory, Hugo Münsterberg [top fiction books of all time TXT] 📗
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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
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