For No. 5 the averages are for two sets of 18 each; for all the others there are 24 in each set.
TABLE XIII.
ELECTRICAL STIMULUS REACTION TIME. SERIES 3.
| Frog. | Average of all. | Average Mean Var. | Average of all. | Average of 1st h. | Average of 2d h. | Mean Var. of Sets. |
|---|---|---|---|---|---|---|
| 1 | 93.6σ | 13.5σ | 91.8σ | 93.2σ | 90.4σ | 13.5σ |
| 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.
The spinal reflex for a decapitated frog, as results previously discussed show, is approximately 50σ; 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 30σ, so if allowance be made in case of the reactions to the four-cell stimulus, the mean becomes about 70σ, 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 70σ and 150σ there is a break. (In tables XI., XII. and XIII., allowance must always be made for the slack in the thread, by subtracting 30σ.) 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 50-80σ, to 140 or 150σ, which may perhaps be taken as the typical instinctive reaction time. From 150σ 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 8σ, 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 σ)
| Mean | First Half. | Second Half. | Mean Variation. | Frog. | |
|---|---|---|---|---|---|
| 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 |