REACTION-TIME AFTER DISCRIMINATION.
Project Gutenberg EPUB3 edition
James, William
0.105 and 0.117;
that for distinguishing the letter A in ordinary print from the letter Z:
0.142 and 0.137;
that for distinguishing a given letter from all the rest of the alphabet (not reacting until that letter appeared)
0.119 and 0.116;
that for distinguishing a word from any of twenty-five other words, from
0.118 sec. to 0.158 sec.
The difference depending on the length of the words and the familiarity of the language to which they belonged.
Prof. Cattell calls attention to the fact that the time for distinguishing a word is often but little more than that for distinguishing a letter:
"We do not, therefore, distinguish separately the letters of which a word is composed, but the word as a whole. The application of this in teaching children to read is evident."
He also finds a great difference in the time with which various letters are distinguished, E being particularly bad.[437]
I have, in describing these experiments, followed the example of previous writers and spoken as if the process by which the nature of the signal determines the reaction were identical with the ordinary conscious process of discriminative perception and volition. I am convinced, however, that this is not the case; and that although the results are the same, the form of consciousness is quite different. The reader will remember my contention (supra, p. 90 ff.) that the simple reaction-time (usually supposed to include a conscious process of perceiving) really measures nothing but a reflex act. Anyone who will perform reactions with discrimination will easily convince himself that the process here also is far more like a reflex, than like a deliberate, operation. I have made, with myself and students, a large number of measurements where the signal expected was in one series a touch somewhere on the skin of the back and head, and in another series a spark somewhere in the field of view. The hand had to move as quickly as possible towards the place of the touch or the spark. It did so infallibly, and sensibly instantly; whilst both place and movement seemed to be perceived only a moment later, in memory.
These experiments were undertaken for the express purpose of ascertaining whether the movement at the sight of the spark was discharged immediately by the visual perception, or whether a 'motor-idea' had to intervene between the perception of the spark and the reaction.[438] The first thing that was manifest to introspection was that no perception or idea of any sort preceded the reaction. It jumped of itself, whenever the signal came; and perception was retrospective. We must suppose, then, that the state of eager expectancy of a certain definite range of possible discharges, innervates a whole set of paths in advance, so that when a particular sensation comes it is drafted into its appropriate motor outlet too quickly for the perceptive process to be aroused. In the experiments I describe, the conditions were most favorable for rapidity, for the connection between the signals and their movements might almost be called innate. It is instinctive to move the hand towards a thing seen or a skin-spot touched. But where the movement is conventionally attached to the signal, there would be more chance for delay, and the amount of practice would then determine the speed. This is well shown in Tischer's results, quoted on p. 524, where the most practised observer, Tischer himself, reacted in one eighth of the time needed by one of the others.[439] But what all investigators have aimed to determine in these experiments is the minimum time. I trust I have said enough to convince the student that this minimum time by no means measures what we consciously know as discrimination.
It only measures something which, under the experimental conditions, leads to a similar result. But it is the bane of psychology to suppose that where results are similar, processes must be the same. Psychologists are too apt to reason as geometers would, if the latter were to say that the diameter of a circle is the same thing as its semi-circumference, because, forsooth, they terminate in the same two points.[440]