Sixteen Experimental Investigations from the Harvard Psychological Laboratory - Hugo Münsterberg (best life changing books txt) 📗
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make it remain rigidly motionless, have on the primary organic rhythms
of the organism, such as the heart-beat, respiration, and peristalsis.
It is also directly in the line of our investigation to inquire how
they affect reflex movements, or the reaction time for any other
stimulus—what happens to the reaction time for an electrical
stimulus, for example, if a loud noise precede or accompany the
electrical stimulus.
For the purpose of determining the range of hearing in the frog, I was
driven to study the influence of sounds upon respiration. Although the
animals did not make any detectable movement, not even of an eyelid,
in response to noises, it seemed not improbable that if the sounds
acted as auditory stimuli at all, they would in some degree modify the
form or rate of the respiratory movement.
C. Influence of Sounds on Respiration.[16]
[16] For full discussion of the normal respiratory movements of
the frog see Martin, Journal of Physiology, Vol. 1., 1878,
pp. 131-170.
The method of recording the respiration was the direct transference of
the movement of the throat by means of a pivoted lever, one end of
which rested against the throat, while the other served as a marker on
a revolving drum carrying smoked paper. The frog was put into a small
box, visual stimuli were, so far as possible, excluded and the lever
was adjusted carefully; a record was then taken for at least half a
minute to determine the normal rate of respiration in the absence of
the stimulus whose effect it was the chief purpose of the experiment
to discover. Then, as soon as everything was running smoothly, the
auditory stimulus was given. The following records indicate the
effects of a few stimuli upon the rate of breathing:
1. Stimulus, 100 V. tuning fork.
Number of respirations for 10 cm. before stimulus 18.0, 17.0; number
of respirations for 10 cm. after stimulus 19.0, 17.3.
The records indicate very little change, and contradict one another.
For the same stimulus the experiment was tried of taking the normal
respiration record for a complete revolution of the drum, and then at
once taking the record for the same length of time (about two minutes)
with the tuning-fork vibrating close to the frog. The following result
is typical and proves that the sound has little effect.
Number of respirations in a revolution before stimulus: First rev.
88; second rev. 88. Number of respirations in a revolution during
stimulus: First rev. 87; second rev. 88.
Concerning the influence of tuning-fork stimuli more will be said
later in a consideration of the effects of auditory stimuli upon
reactions to visual stimuli.
2. The influence of falling water as an auditory stimulus. Water was
allowed to fall about two feet in imitation, first, of a plunging
frog, and second, of water falling over rocks. In representing the
effect of the stimulus on the rate of respiration, I have given the
distance on the drum covered by the ten complete respirations just
preceding the stimulus and the ten following it.
10 Respirations. 10 Respirations.
Before Stimulus. After Stimulus.
1st Stim. 13.0 cm. 11.8 cm.
2d Stim. 12.7 cm. 12.7 cm.
With a smaller animal.
1st Stim. 5.4 cm. 4.8 cm.
2d Stim. 4.9 cm. 4.7 cm.
Average for 5 5.00 cm. 4.86 cm.
_These records show a marked increase in the rate of respiration just
after the auditory stimulus is given for the first time._ The stimulus
has less effect when repeated after an interval of one or two minutes,
and if repeated several times it finally causes no noticeable change.
On the whole, the sound of falling water seems to arouse the animals
to fuller life. The stimulus appears to interest them, and it
certainly accelerates respiration. This is precisely what one would
expect from a sound which is of special significance in the life of
the animal.
3. In case of a loud shrill whistle inhibition of respiration
resulted. This probably means that the frogs were frightened by the
sound. Falling water served rather to excite their natural-habitat
associations, whereas, the whistle, being an uncommon and unassociated
sound, caused fear. It is evident to the casual observer that the frog
sometimes inhibits and sometimes increases its respiratory movements
when frightened, so the result in this experiment is in no way
surprising. I am by no means certain, however, that a longer series of
observations on several individuals would give constant inhibitory
results. My immediate purpose in the work was to get evidence of
hearing; the respiratory changes were of secondary importance,
although of such great interest that I have planned a more thorough
special study of them for the future.
A few sample results showing the influence of the whistle upon a small
bull-frog follow:
Length of 10 Resps. Length of 10 Resps.
Before Stimulus in cm. After Stimulus in cm.
1st Stim. 6.0 6.7
2d ” 5.4 6.0
3d ” 5.9 5.8
1st ” 4.7 5.4
2d ” 4.4 4.6
As a test-check observation for comparison, the influence of a visual
stimulus upon respiration was noted under the same conditions as for
the auditory. Effect of turning on electric light over box.
Length in cm. of 10 Resps. Length in cm. of 10 Resps.
Before Stimulus. After Stimulus.
4.8 4.4
5.3 4.6
4.5 4.0
These results indicate an increase in the respiration rate due to the
visual stimulus.
4. Of the other auditory stimuli used, the pistol-cap explosion gave
very irregular results. For one animal it caused acceleration, for
another inhibition. There is, however, good evidence that the sounds
were heard.
5. The ringing of a bell gave results similer to those for a whistle,
and the sound of a 500 S.V. tuning fork usually caused a slight
increase in the rate of breathing. In these experiments I therefore
have evidence, through their effects upon respiration, of the frog’s
ability to hear sounds ranging from 50 V. to at least 1,000 V.
The croak of the green frog ranges from 100 to 200 V., so far as I
have been able to determine. That of the bull frog is lower, from 50
to 75; and in the leopard frog the range is from 80 to 125. The latter
is very different from the green frog in its croaking, in that it
croaks whenever disturbed, whereas, the green frog rarely responds in
that way to a stimulus.
We are now in a position to say that the failure of frogs to give
motor reactions to strong auditory stimuli is not due to their
inability to be affected by the stimuli, but is a genuine inhibition
phenomenon.
XI. THE EFFECTS OF AUDITORY STIMULI ON VISUAL REACTIONS.
Further experimental evidence of hearing was gotten from some work
done to test the influence of sounds upon motor reactions to visual
stimuli. Frogs, like most other amphibians, reptiles and fishes, are
attracted by any small moving object and usually attempt to seize it.
They never, so far as I have noticed, feed upon motionless objects,
but, on the other hand, will take almost anything which moves.
Apparently the visual stimulus of movement excites a reflex. A very
surprising thing to those who are unfamiliar with frog habits is the
fear which small frogs have of large ones. Put some green frogs or
small bull frogs into a tank with large bull frogs, and the little
ones will at once show signs of extreme fear; they jump about in the
most excited manner and try hard to escape. The cause of their fear
soon appears, since it is usually only a few minutes until the little
ones are swallowed by their wide-mouthed, cannibalistic fellows.
It is, moreover, well known that a bit of red flannel fastened to a
hook attracts frogs and is an excellent method of capturing them. Red
seems to be the color which they most readily notice.
This tendency of the frog to attempt to seize any moving object I made
use of to test the value of sounds. By placing a frog in a glass
aquarium which was surrounded by a screen, back of which I could work
and through a small hole in which I was able to watch the animal
without being noticed by it, and then moving a bit of red cardboard
along one side of the aquarium, I could get the frog to jump at it
repeatedly. In each attempt to get the moving object, the animal
struck its head forcibly against the glass side of the aquarium. There
was, therefore, reason to think that a few trials would lead to the
inhibition of the reaction. Experiment discovered the fact that a
hungry frog would usually jump at the card as many as twenty times in
rapid succession.
In this reaction to a visual stimulus there appeared good material for
testing audition. I therefore arranged a 500 S.V. tuning fork over the
aquarium and compared the reactions of animals to the visual stimulus
alone, with that to the visual stimulus when accompanied by an
auditory stimulus. The tuning-fork sound was chosen because it seemed
most likely to be significant to the frog. It is similar to the sounds
made by the insects upon which frogs feed. For this reason one would
expect that the sight of a moving object and the sound of a
tuning-fork would tend to reënforce one another.
The experiments were begun with observations on the effects of moving
objects on the respiration. In case of a normal rate of 54
respirations per minute sight of the red object caused an increase to
58. Then the same determination was made for the auditory stimulus.
The tuning-fork usually caused an increase in rate. In a typical
experiment it was from 65 per minute to 76. The observations prove
conclusively that the 500 S.V. sound is heard. My attention was turned
to the difference of the environment of the ear in its relation to
hearing. Apparently frogs hear better when the tympanum is partially
under water than when it is fully exposed to the air.
Having discovered by repeated trials about how vigorously and
frequently a frog would react to the moving red card, I tried the
effect of setting the fork in vibration a half minute before showing
the card. It was at once evident that the sound put the frog on the
alert, and, when the object came into view, it jumped at it more
quickly and a greater number of times than when the visual stimulus
was given without the auditory. This statement is based on the study
of only two animals, since I was unable to get any other frogs that
were in the laboratory at the time to take notice of the red
cardboard. This was probably because of the season being winter. I
venture to report the results simply because they were so definite as
to point clearly to the phenomenon of the reënforcement of the
visual-stimulus reaction by an auditory stimulus.
Concerning the influence of this combining of stimuli on the reaction
time, I am only able to say that the reaction to the moving object
occurred quicker in the presence of the auditory stimulus. When the
red card was shown it was often several seconds before the frog would
notice it and attempt to get it, but when the sound also was given the
animal usually noticed and jumped toward the moving card almost
immediately.
Unfortunately I have thus far been unable to get chronoscopic
measurements of the reaction times in this reënforcement phenomenon. I
hope later to be able to follow out the interesting suggestions of
these few experiments in the study
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