Various - Harvard Psychological Studies, Volume 1

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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 association, 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 classes:
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 class 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.: 'Vorlaeufiger Bericht ueber die
Portpflanzungsgeschwindigkeit der Nervenreizung.' _Arch. f.
Anal. u. Physiol._, 1850, S. 71-73.

[5] Exner, S.: 'Experimentelle Untersuchung der einfachsten
psychischen Processe.' _Pflueger'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. Anal. 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 fuer die Erforschung des
Reflexmechanismus in Lendentmark des Frosches.' _Berichte ueber
die Verhandlungen der Kgl. saechs. Gesellsch. d. Wissensch. zu
Leipzig_, 1867, S. 3.

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

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

[12] Schrader, M.G.: 'Zur Physiologie des Froschgehirns.'
_Pflueger's Arch._, Bd. 41, 1887, S. 75-90.

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

[14] Merzbacher, L.: 'Untersuchungen ueber die Regulation der
Bewegungen der Wirbelthiere. I. Beobachtungen an Froeschen.'
_Pflueger'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_) quantitative, (_c_) for different
strengths of current; (2) Determination of reaction time to tactual
stimuli (with the same variations); (3) Auditory: (_a_) qualitative,
(_b_) quantitative, with studies on the sense of hearing; (4) Visual:
(_a_) qualitative, (_b_) quantitative, with observations concerning
the importance of this sense in the life of the frog, and (5)
Olfactory: (_a_) qualitative, (_b_) quantitative.

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 passing 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 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 deg. 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 deg. 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.

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 277 reactions.]

The column of figures at the left indicates the number of reactions at
any point. Below the base line are the classes. For convenience of
plotting the reactions have been grouped into classes which are
separated by 25[sigma]. Class 1 includes all reactions between
1[sigma] and 25[sigma], class 2 all from 25[sigma] to 50[sigma], and
so on to 400[sigma], thereafter the classes are separated by
100[sigma]. It is noticeable that there is one well-marked mode at
75[sigma]. A second mode occurs at 175[sigma]. This is the primary and
in our present work the chiefly significant mode, since it is that of
the quick instinctive reaction to a stimulus. At 500[sigma] there is a
third mode; but as such this has little meaning, since the reactions
are usually pretty evenly distributed from 300[sigma] on to
2000[sigma]; if there is any grouping, however, it appears to be about
500[sigma] and 800[sigma].

The first mode has already been called the reflex mode. The short
reactions referred to usually lie between 40[sigma] and 80[sigma], and
since experiment has shown conclusively that the spinal reflex
occupies about 50[sigma], there can be little doubt that the first
mode is that of the reflex reaction time.

The second mode represents those reactions which are the result of
central activity and control. I should be inclined to argue that they
are what we usually call the instinctive and impulsive actions. And
the remaining reactions represent such as are either purely voluntary,
if any frog action can be so described, or, in other words, depend
upon such a balancing of forces in the brain as leads to delay and
gives the appearance of deliberate choice.

Everything points to some such classification of the types as follows:
(1) Stimuli strong enough to be injurious cause the shortest possible
reaction by calling the spinal centers into action, or if not spinal
centers some other reflex centers; (2) slightly weaker stimuli are not
sufficient to affect the reflex mechanism, but their impulse passes on
to the brain and quickly discharges the primary center. There is no
hesitation, but an immediate and only slightly variable reaction; just
the kind that is described as instinctive. As would be expected, the
majority of the frog's responses are either of the reflex or of this
instinctive type. (3) There is that strength of stimulus which is not
sufficient to discharge the primary center, but may pass to centers of
higher tension and thus cause a response. This increase in the
complexity of the process means a slower reaction, and it is such we
call a deliberate response. Precisely this kind of change in neural
action and in reaction time is at the basis of voluntary action. And
(4) finally, the stimulus may be so weak that it will not induce a
reaction except by repetition. Just above this point lies the
threshold of sensibility, the determination of which is of
considerable interest and importance.

_Group 2 of the electrical reactions_ consists of three series taken
to determine the relation of strength of stimulus to reaction time.
The conditions of experimentation differed from those for group 1 in
the following points: (1) The stimulus was applied directly by the
making of a circuit through wires upon which the subject rested (Fig.
9); (2) the thread was attached to the right hind leg; (3) the thread,
instead of being kept at the tension given by the 5-gram weight as in
the former reactions, was slackened by pushing the upright lever of
the reaction key one eighth of an inch toward the animal. This was
done in order to avoid the records given by the slight twitches of the
legs which precede the motor reaction proper. For this reason the
reactions of group 2 are not directly comparable with those of group
1. Fig. 9 is the plan of the bottom of a reaction box 15 cm. at one
end, 30 cm. at the other, 60 cm. long and 45 cm. deep. On the bottom
of this, at one end, a series of interrupted circuits were arranged as
shown in the figure. The wires were 1.2 cm. apart, and an animal
sitting anywhere on the series necessarily touched two or more, so
that when the stimulus key, X, was closed the circuit was completed by
the animal's body; hence, a stimulus resulted. The stimulus key, X,
was a simple device by which the chronoscope circuit, _c_, _c_, was
broken at the instant the stimulus circuit, _s_, _c_, was made.