| Abstract: | Pigeons were trained in an operant, go/no-go, discrimination by successive presentations of discrete, positive and negative trials. In separate groups, the rate of discriminaion learning based on an auditory cue, on visual cues of different discriminability, and on combined auditory and visual cues was determined. The auditory cue was tone/no-tone, the visual cue was a difference in brightness level on the key. Following discrimination training, stimulus control was tested in extinction by presenting tone or notone at each of four key-brightness levels.Learning was more rapid with two cues than with either cue singly, demonstrating summation. The contribution made by the tone cue to the learning of the discrimination decreased with increasing discriminability of the light cue. The control exerted by the tone cue also decreased (i.e., the tone cue was overshadowed) with increasing discriminability of the light cue. In certain cases, the tone cue decreased control by brightness, showing that in two-cue discriminations each cue may reduce the control exerted by the other. |
