Delay of Reward and Human Motor Learning
It is encouraging whenever a relationship discovered at the subhuman level is found to hold at the human level. Such a relationship perhaps holds between learning speed and delay of reward. Saltzman (6) recently investigated the effect of delaying reward on the rate of learning in human Ss. The learning material in the experiment was a list of 4-place numbers and the reward was informing the S that a correct response had been made. The results of that experiment are in agreement with the results of a number of similar studies with animals (1, 3, 4, 5 ) . In the animal studies, learning is slowed down when the reward is delayed; similarly, in the above-mentioned study with humans, learning was slowed down when the reward was delayed. Since delay of reward has been found to influence noticeably the rate of human verbal learning, as well as the rate of animal learning, it was felt that a similar effect of delay of reward on human motor learning could easily be demonstrated experimentally. It was the purpose of the present study to investigate this relationship. Specifically, this experiment was designed to study the effect of delaying reward on the speed with which human Ss learn a simple motor task. Reward in the situation was defined as informing the S that his response was correct. PROCEDURE AND APPARATUS The Ss were 90 Indiana University undergraduate men and women, randomly divided into 3 groups of 30. Each S was seated co~nfortably at a table and the following instructions were read to him: W e want to see how quickly you can learn to draw a 3-in. line when you are blindfolded. I am going to blindfold you and give you a pencil and place your hand with the pencil in it in position on this (blank) sheet of paper. When I say 'Go,' I want you to draw a 3-in. horizontal line. As soon as you have finished drawing what you believe to be a line 3 in. long, lift the pencil from the paper and then put it right down again. This will indicate to me that you have finished, and then, I shall tell you something about the line that you have just drawn. If the line is 3 in. long, I shall say 'Right;' if it is between 2 in. and 4 in. long, but not 3 in. long, I shall say 'Wrong;' if the line is less than 2 in. long, I shall say 'Too short;' and if it is over 4 in. long, I shall say 'Too long.' So there will be 4 different kinds of comments that I can make: 'Right,' if the line is 3 in. long, 'Wrong,' if the line is between 2 and 4 in. long, but not 3 in. long, 'Too short,' if the line is less than 2 in. long, and 'Too long,' if it is more than 4 in.