534 J. M. CATTELL : TABLE XL. B C Reaction-time for Li fr ht 150 150 Perception-time for Ligh t 30 50 a Colour 90 100 a Picture 100 110 a Letter 190 1^0 a (short) Word 1-70 130 Will time for Colours 980 400 Pictures 9nO 280 Letters 140 170 Words. . . 100 110 We have thus found the time it takes us to see and name the objects which we spend a great part of our life in seeing and naming. We have not been dealing with artificial processes or things outside the circle of our natural interests. If in the course of evolution, as is probable, the molecular arrangement of the nervous system becomes more sensitive and delicately balanced, we may suppose that the times taken up by our mental processes, become shorter, and we live so much the longer in the same number of years. It will therefore be of great interest to make experiments such as these on the lower races, as well as on per- sons of different age, sex, occupation, &c. V. The Influence of Attention, Fatigue and Practice on the Duration of Cerebral Operations. We have seen that while the time of a reaction is somewhat lengthened when the brain cannot so well prepare itself, it does not vary greatly with different degrees of Attention. I have made similar determinations for cerebral operations in which complica- tions have been added to the simple reaction-time. I chose as typical cases the time it takes to see a white surface and show this by a motion of the hand, and the time it takes to see and name a letter. On the one hand the observer tried by great con- centration of the attention and effort to react as quickly as possible ; on the other hand the impression was produced at irregular intervals (three-fourths to fifteen seconds), so that the brain could not be held in a maximum state of readiness. We find, from Table XLL, under the two degrees of attention or preparation a difference in the times of seeing and reacting on the white surface of 75<r for B, 15 for C ; in the time of seeing and naming a letter 29<r for B, 25 for C.
