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This eBook from the Gutenberg Project consists of approximately 678 pages of information about Harvard Psychological Studies, Volume 1.
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

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