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

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