REACTION TIME FOR TACTUAL AND ELECTRICAL STIMULI.

Tactual Reaction Time.  Electrical Reaction Time.

Frog.  Average.  Mean Variation.  Average.  Mean Variation.

1         188.3[sigma]                167.3[sigma]
2         199.1                        180.1
3         212.1
4         213.0                        210.3
5¹        199.8                        138.5
6         221.9                        164.4
Gen. Avs.  205.7      33.8              172.1       34.3

  ¹For 5 the average of ten instead of twenty is given.

VIII.  EQUAL VARIABILITY AS A CRITERION OF COMPARABILITY OF REACTION TIME FOR DIFFERENT KINDS OF STIMULI.

Since variability as indicated in the study of the influence of different strengths of electrical stimulus becomes less as the stimulus increases, parity in variability for different stimuli offers a basis for the comparison of reaction times.  Certain it is that there is no use in comparing the reaction times for different senses or different qualities of stimuli unless the relative values of the stimuli are taken into consideration; but how are these values to be determined unless some such index as variability is available?  If the reaction time to tactual stimuli as here presented is to be studied in its relation to the electrical reaction time, it will mean little simply to say that the former is longer than the latter, because the electrical reaction time for a one-cell stimulus happens to be somewhat less than that for the particular tactual stimulus used.  For it is clear that this tactual reaction time is really shorter than the reaction time to a weak current.  In making variability a basis of comparison it must be assumed that the strength of stimulus is the important factor, and that all other variable conditions are, so far as possible, excluded.  If, now, on the basis of parity in variability we compare the tactual and electrical reaction times, it is apparent that the tactual is considerably longer.  The tactual average of Table XV. is 205.7[sigma], while the electrical reaction time which has approximately the same variability is 172.1[sigma].  It may well be objected that I have no right to make variability the basis of my comparison in these experiments, because the work for the various kinds of stimuli was done under different conditions.  Admitting the force of this objection, and at the same time calling attention to the fact that I do not wish to lay any stress on the results of the comparisons here made, I take this opportunity to call attention to the possibility of this criterion.

The use of variability as a basis of comparison would involve the assumptions (1) that a certain intensity of every stimulus which is to be considered is capable of producing the shortest possible, or reflex reaction, and that this reaction is at the same time the least variable; (2) that as the strength of a stimulus decreases the variability increases until the threshold is reached.