Page:Mind (Old Series) Volume 11.djvu/380

 THE TIME TAKEN UP BY CEREBEAL OPERATIONS. 379 a corrected average eliminates all premature reactions. I give in the Tables the number of false reactions made ; 1 it would have been well if v. Kries and Auerbach, Merkel and others had done the same. We can now examine the Table giving the time needed to perceive and react on a white surface. TABLE XII. ] B ( ^ R V R' V R V R' V 14.1 203 g 203

2^Q 14 94fi 7 19 217 18 213 12 219 13 217 10 20 222 22 222 15 226 n 226 q 31 234 35 91 7 1 1 9'3Q 1 ^ 941 in 2. II 219 21 214 13 215 Ifi 21 7 11 3 214 207 30 20 206 203 18 7 216 256 12 20 219 254 7 10 25. Ill 239 28 234 21 250 19 253 15 31 212 215 19 SJ. 205 205 6 15 263 244 22 16 259 248 9 9 2. VII 189 191 183 213 I CO CD CM f 5 I 1 I-H i-H i- 186 189 185 21 9 6 7 8 245 251 246 262 10 11 17 7 242 252 242 262 7 5 12 4 4 209 13 910 8 251 11 251 6 A. . 211 20 207 11 241 14 242 9 The simple reaction-time for B and C is about 150<r, therefore (on our hypothesis as to the nature of the cerebral operations, and assuming, though not without hesitation, that the corresponding physiological processes take up the same time as in the simple reaction) the time needed for the nervous impulse to travel from the thalami to the centre for sight in the cortex and excite the cells there so as to call forth the sensation of a light, and for a will-impulse to be prepared there and sent thence to the motor centre, was for B 61, for C 95 y. We may suppose that the time of the centripetal and centrifugal progress through the brain is about the same, and that the time used in the cortex is about equally divided between the perception of the light and the preparation of the motor impulse ; at all events the whole time is so short that, if we divide it equally between the processes of per- ception and volition, the error cannot be great. We therefore set the perception-time for light, where the nature of the light need 1 After " false," the entire number made during the series given in the column under which it stands.