Effects of stimulus similarity in discrimination training upon wavelength generalization in pigeons

Thirty pigeons were given variable interval training to peck a 555-nm. light and then were tested for wavelength generalization. The subjects were later assigned to 1 of 3 groups, matched for both relative generalization slope and response rate. One group then received successive discrimination training between the 555-nm. stimulus (S+) and a vertical white line on a 555-nm. background (S minus); another group experienced the same S+ but a vertical white line on a black background as S minus. A third group received a comparable amount of single stimulus training with the 555-nm. value. On a second wavelength generalization test, the first group yielded greater sharpening of generalization than the second group, whereas the third group showed no change from Test 1. These results indicate that the sharpening of generalization gradients by discrimination training is directly related to the similarity of the discrimination training stimuli.