Inhibitory stimulus control following errorless discrimination learning

Three generalization procedures were used to investigate inhibitory stimulus control following discrimination learning with few errors. Three groups of pigeons acquired a discrimination between a green stimulus (the positive stimulus) and a vertical or horizontal line (the negative stimulus) through differential autoshaping followed by multiple schedule presentation of the two stimuli with gradually increasing stimulus durations. Genereralization testing was along a line-tilt continuum. For one group, the test involved a resistance-to-reinforcement procedure in which responses to all line tilts were reinforced on a variable-interval schedule. For a second group, also tested with the resistance-to-reinforcement procedure, the lines were superimposed on the green field that formerly served as the positive stimulus. A third group was tested in extinction with the combined stimuli. Control groups had no discrimination training but responding to green was nondifferentially reinforced. The control subjects responded more to all line tilts during testing than did the comparable experimental subjects, indicating that the negative stimulus had become an inhibitory stimulus. Both resistance-to-reinforcement groups revealed inhibitory gradients around the negative stimulus, but the gradient for the extinction group was relatively flat. These data are consistent with others that modify Terrace's early conclusion concerning the failure of inhibition to develop during errorless training.