Page:Mind (Old Series) Volume 11.djvu/525

IV. KESEARCH. THE TIME TAKEN UP BY CEREBRAL OPERATIONS. 1 By JAMES McKEEN CATTELL, Ph.D. Assistant in the Psychological Laboratory, University of Le/'j IV. The Will-time* In the experiments described in the foregoing section the motion to be made was always the same, and took up the same or about the same time. In this section the nature of the motion depends on the nature of the impression. The experiments about to be described will throw further light on the Perception-time, but we shall find in addition a variable Will- (or Motor) time. The percep- tion-process, further, is different from what we considered in the foregoing section : then the observer expected a certain impres- sion and saw whether it was present or not ; in the experiments now to be described the observer, not awaiting a given impression, had to identify the one occurring. We might perhaps expect the perception to be more difficult and consequently to last longer in the latter case ; the experiments however show that there can be no great difference in the time. Experiments have been made in this direction by Donders 3 and others, they letting the observer lift his right hand if (for example) the light is red, the left if it is blue. Under Wundt's direction Merkel 4 extended this method, the observer lifting a different finger for each of ten different impressions. My first experiments (carried out in the winter 1883-4) were made with aid of electric lights, as above described, and were similar to those of previous experimenters ; they gave as the time for distinguishing the colour and choosing the motion 120<r for B, 168 for C. Afterwards I used the gravity chronoscope, which enabled me to use daylight reflected from coloured surfaces. The current controlling the chronoscope was led through two keys (K and K' Fig. 8, MIND 42), the observer holding one closed with his right, the other with his left hand. Two colours, say red and blue, were used in the same 1 Concluded from MIND 42 and 43. - I use the term 'Will-time' for luck of a better; in Germany 'Wahlzeit' is used. Tin' motion is in most cases simply the result of tin- perception, and 'Association-time' might be used, were it not already taken up. 'Motor tinif' would perhaps best explain the process, but might cause confusion. 3 Arch, fur Anaf. it. I'hi/xiol., 1868. 4 1'h II. Stn,li,;i, ii. 1.