Sixteen Experimental Investigations from the Harvard Psychological Laboratory - Hugo Münsterberg (best life changing books txt) 📗
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attempt has thus far been made to get the reaction time in case of
summation effects except in occasional instances, and in so far as
those are available they indicate no great difference between the
normal threshold reaction and the summation reaction, but on this
problem more work is planned.
There are large mean variations in Table XI., as would be anticipated.
Since the reactions were taken in sets of 24, the means of each set as
well as that of the total are given, and also, in columns 4 and 5, the
means of the first half and the last half of each set.
A comparison of Tables XI., XII. and XIII. makes clear the differences
in reaction time correlated with differences in the strength of an
electric stimulus. For Table XI., series I, the relative value of the
stimulus was I; for Table XII., series 2, it was 2, and for Table
XIII., series 3, it was 4. Throughout the series from I to 3 there is
a rapid decrease in the reaction time and in the variability of the
same. The reaction time for stimulus I, the so-called threshold, is
given as 300.9[sigma]; but of the three it is probably the least
valuable, for reasons already mentioned. The mean of the second
series, stimulus 2, is 231.5[sigma] while that of the third, stimulus
4, is only 103.1[sigma]. This great reduction in reaction time for the
four-cell stimulus apparently shows the gradual transition from the
deliberate motor reaction, which occurs only after complex and varied
central neural activities, and the purely reflex reaction, which takes
place as soon as the efferent impulse can cause changes in the spinal
centers and be transmitted as an afferent impulse to the muscular
system.
TABLE XI.
ELECTRICAL STIMULUS REACTION TIME. SERIES 1.
Average Average of Average Average Mean Var
Frog. of all. Mean Var. Sets. of 1st h. of 2d h. of Sets.
1 238.5* 33.3* 216.0* 205.6* 226.7* 33.2*
261.0 248.0 274.1 33.3
2 458.0 219.0 458.0 270.4 643.8 219.0
4 273.4 59.9 273.4 245.7 301.1 59.9
5 263.9 50.5 268.6 244.7 292.5 44.9
259.2 236.0 282.4 56.1
6 271.1 65.1 322.6 273.2 372.0 87.9
219.6 208.5 230.6 42.3
Gen Av. 300.9 85.5 300.9 244.8 356.8 85.5
Totals.
For No. 1 the averages are for 2 sets of 24 reactions each, 48
” 2 ” ” one set of 12 ” ” 12
” 4 ” ” one set of 24 ” ” 24
” 5 ” ” two sets of 24 ” ” 48
” 6 ” ” two sets of 24 and 12 reactions,
respectively, 36
*Transcriber’s Note: All values in [sigma], 1/1000ths of a second.
TABLE XII.
ELECTRICAL STIMULUS REACTION TIME. SERIES 2.
Average Average of Average Average Mean Var
Frog. of all. Mean Var. Sets. of 1st h. of 2d h. of Sets.
1 227.3* 33.7* 229.4* 209.1* 249.6* 25.5*
225.2 207.3 243.0 42.1
2 240.1 30.9 239.0 222.3 255.1 29.0
241.3 220.2 262.4 32.8
4 270.3 56.5 298.5 285.3 311.4 62.8
242.2 206.0 278.4 50.2
198.5 26.2 195.0 197.5 193.0 33.5
202.0 195.2 209.0 18.8
6 224.4 24.4 221.6 209.7 233.7 23.6
227.2 213.5 241.0 25.1
Gen. Av. 231.5 34.3 231.0 216.6 246.6 34.3
For No. 5 the averages are for two sets of 18 each; for all the
others there are 24 in each set.
*Transcriber’s Note: All values in [sigma], 1/1000ths of a second.
TABLE XIII.
ELECTRICAL STIMULUS REACTION TIME. SERIES 3.
Average Average Average Average Mean Var.
Frog. of all. Mean Var. of all. of 1st h. of 2d h. of Sets.
1 93.6* 13.5* 91.8* 93.2* 90.4* 13.5*
95.4 91.8 99.0 13.5
2 99.9 12.8 92.2 89.4 95.0 17.4
107.5 105.9 109.0 8.2
4 125.2 16.3 113.5 106.5 120.5 13.6
136.0 135.7 138.2 19.0
5 94.4 8.0 88.6 90.5 88.6 8.2
100.2 97.8 102.7 7.9
6 102.5 12.2 104.2 98.6 109.9 12.8
100.9 101.0 108.3 11.6
Gen. Avs. 103.1 12.5 103.1 101.0 105.9 12.5
For each animal there are two sets of 24 reactions each.
*Transcriber’s Note: All values in [sigma], 1/1000ths of a second.
The spinal reflex for a decapitated frog, as results previously
discussed show, is approximately 50[sigma]; and every time the
four-cell stimulus is given this kind of a reaction results. There is
a slight twitch of the legs, immediately after which the animal jumps.
Now for all these series the thread was slackened by one eighth of an
inch, but the reflex time was determined without this slack.
Calculation of the lengthening of the reaction time due to the slack
indicated it to be between 20 and 30[sigma], so if allowance be made
in case of the reactions to the four-cell stimulus, the mean becomes
about 70[sigma], or, in other words, nearly the same as the spinal
reflex. The conclusion seems forced, therefore, that when a stimulus
reaches a certain intensity it produces the cord response, while until
that particular point is reached it calls forth central activities
which result in much longer and more variable reaction times. It was
said above that the series under consideration gave evidence of the
gradual transition from the reflex to the volitional in reaction time.
Is this true, or do we find that there are well-marked types, between
which reactions are comparatively rare? Examination of the tables
VII., VIII., IX., XI., XII. and XIII. will show that between 70[sigma]
and 150[sigma] there is a break. (In tables XI., XII. and XIII.,
allowance must always be made for the slack in the thread, by
subtracting 30[sigma].) All the evidence furnished on this problem by
the electrical reaction-time studies is in favor of the type theory,
and it appears fairly clear that there is a jump in the reaction time
from the reflex time of 50-80[sigma], to 140 or 150[sigma], which may
perhaps be taken as the typical instinctive reaction time. From
150[sigma] up there appears to be a gradual lengthening of the time as
the strength of the stimulus is decreased, until finally the threshold
is reached, and only by summation effect can a response be obtained.
The most important averages for the three series have been arranged in
Table XIV. for the comparison of the different subjects. Usually the
reaction time for series 3 is about one half as long as that for
series 2, and its variability is also not more than half as large. In
the small variability of series 3 we have additional reason for
thinking that it represents reflexes, for Table IX. gives the mean
variation of the reflex as not more than 8[sigma], and the fact that
the means of this series are in certain cases much larger is fully
explained by the greater opportunity for variation afforded by the
slack in the thread.
TABLE XIV.
MEANS, ETC., FOR EACH SUBJECT FOR THE THREE SERIES. (TIME IN [sigma])
Mean First Second Mean Frog.
Half. Half. Variation.
Series 1 238.5 226.8 259.4 33.3
Series 2 227.3 208.2 246.3 33.7 No. 1
Series 3 93.6 92.5 94.7 13.5
Series 1 458.0 270.4 643.8 219.0
Series 2 240.1 221.2 258.8 30.9 No. 2
Series 3 99.9 97.6 102.0 12.8
Series 1 273.4 245.7 301.1 59.9
Series 2 270.3 245.6 294.9 56.5 No. 4
Series 3 125.2 121.1 129.3 16.3
Series 1 263.9 240.4 287.4 50.5
Series 2 198.5 196.4 201.0 26.2 No. 5
Series 3 94.4 94.2 94.7 8.0
Series 1 271.1 240.8 301.3 65.1
Series 2 224.4 211.6 237.3 24.4 No. 6
Series 3 102.5 99.8 109.1 12.2
A striking fact is that the averages for the first and last half of
sets of reactions differ more for the weak than for the strong
stimulus. One would naturally expect, if the increase were a fatigue
phenomenon purely, that it would be greatest for the strongest
stimulus; but the results force us to look for some other conditions
than fatigue. A stimulus that is sufficiently strong to be painful and
injurious to an animal forces an immediate response so long as the
muscular system is not exhausted; but where, as in series 1 and 2 of
the electrical stimulus, the stimulus is not harmful, the reason for a
sudden reaction is lacking unless fear enters as an additional cause.
Just as long as an animal is fresh and unfamiliar with the stimulus
there is a quick reaction to any stimulus above the threshold, and as
soon as a few experiences have destroyed this freshness and taught the
subject that there is no immediate danger the response becomes
deliberate. In other words, there is a gradual transition from the
flash-like instinctive reaction, which is of vast importance in the
life of such an animal as the frog, to the volitional and summation
responses. The threshold electrical stimulus does not force reactions;
it is a request for action rather than a demand, and the subject,
although startled at first, soon becomes accustomed to the experience
and responds, if at all, in a very leisurely fashion. The reaction
time to tactual stimuli, soon to be considered, was determined by
giving a subject only three or four stimulations a day; if more were
given the responses failed except on repetition or pressure; for this
reason the data on fatigue, or lengthening of reaction time toward the
end of a series, are wanting in touch. A few tests for the purpose of
discovering whether the time would lengthen in a series were made with
results very similar to those of the threshold electrical stimulus;
the chief difference lies in the fact that the responses to touch fail
altogether much sooner than do those to the electrical stimulus. This,
however, is explicable on the ground that the latter is a stimulus to
which the animal would not be likely to become accustomed so soon as
to the tactual.
First Half. Second Half. Second % Greater.
Series 1 244.8[sigma] 356.8[sigma] 46 per cent
Series 2 216.6 246.6 14 “
Series 3 101.0 105.9 5 “
If pure fatigue, that is, the exhaustion of the nervous or muscular
system, appears anywhere in this work, it is doubtless in series 3,
for there we have a stimulus which is so strong as to force response
on penalty of death; the reaction is necessarily the shortest
possible, and, as a matter of fact, the motor reaction (jump forward)
here occupies little more time than the leg-jerk of a decapitated
frog. This probably indicates that the reaction is a reflex, and that
the slight increase in its length over that of the spinal reflex is
due to occasional cerebellar origin; but of this there can be no
certainly from the evidence herewith presented. At any rate, there is
no possibility of a voluntary reaction to the strong current, and any
changes in the general character of the reaction time in a series will
have to be attributed to fatigue of the nervous or muscular systems.
The second halves of the sets of series 3 are 5 per cent. longer than
the first, and unless this is due to the partial exhaustion of the
nervous system it is hard to find an explanation of the fact. Fatigue
of the muscles concerned seems out of the question because the
reactions occur at the rate of only one per minute, and during the
rest interval any healthy and well-nourished muscle would so far
recover from the effect of contraction that it would be able to
continue the rhythmic action for long periods.
To the inquiry, Does fatigue in the experiments mean tiring by the
exhaustion of nerve energy, or is the lengthening in reaction time
which would naturally be attributed to tiring due to the fact that
experience has shown quick reaction to be unnecessary? we shall have
to reply that there is evidence in favor of both as
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