Stimulus-Dependent Asymmetry in Classical and Instrumental Discrimination Learning by Pigeons

Two auditory (1- and 2-kHz tones) and two visual (red and white lights) stimuli were used as discriminanda in classical heart rate and instrumental conditioning situations employing the same pigeons as subjects. It was found that while discrimination of the tones was demonstrated easily in the classical situation, a discrimination of the colors was not. Conversely, while discrimination of the colors was achieved quickly in the instrumental situation, a discrimination of the tones was not. These results are discussed in the context of specific learning constraints and viewed as consequences of the adaptation of pigeons to their normal environment.