Page:Mind (Old Series) Volume 11.djvu/386

THE TIME TAKEN UP BY CEEEBRAL OPERATIONS. 385 TABLE XX. I J ( i R V R' V R V R' V 3. II 261 31 260 18 268 12 266 11 27. Ill 234 21 228 12 235 23 229 11 1. IV 205 37 194 23 261 32 255 25 230 206 38 18 220 208 25 6 251 277 24 23 255 281 19 16 A 227 29 222 17 258 23 257 16 It therefore (making the same assumptions as above) took B 47, C 5&T, to see that a small object was on a white surface. The next case to be given is where it was necessary to dis- tinguish one of two letters from the other, A and Z being taken. The averages given are taken from six series. TABLE XXI. I J ( i R V R' V R V R' V 4. 10. XII A Z 315 330 26 31 319 325 16 21 327 348 31 29 323 348 18 21 A 322 28 322 18 337 30 335 19 False.. 3 5 It thus took B 142, C 137<r, to distinguish one letter from an- other, respectively 45 and 31<r longer than to distinguish one colour from another. We now come to consider the time needed to distinguish one letter from all the others ; that is the time it takes to see a letter. This is a process with which our brain is constantly busy ; the time taken up by it is therefore of special interest. If for example the time is different for the several letters, it is a matter of the greatest practical importance, for those letters which it takes the longest to see might be so modified as to shorten the time. If it takes 20<T longer to see E than it would to see a symbol that might be taken in its place, say A, it is startling if we calculate how much time is being wasted and how much unnecessary strain is being put on eye and brain. I have published 1 extended series 1 Phil. Studien, ii. 4 ; Brain, No. 31. 26