Stimulus comparison and perceptual learning: further evidence and evaluation from an imprinting procedure.

Two experiments used chicks to investigate the role of stimulus comparison in perceptual learning. In Experiment 1, chicks received exposure to two views of a jungle fowl, SV (side view) and BV (back view), intermixed within a session (mixed exposure), exposure to SV in one session and BV in a different session (separate exposure), or no exposure to either view. All chicks then received a heat-reinforced discrimination with SV and BV serving as discriminanda. Chicks given mixed exposure acquired the discrimination more readily than did either those given separate exposure or those given no exposure. In Experiment 2, all chicks received mixed exposure to the two stimuli. For one group the interval between presentations of the stimuli was short (short-mixed), for the other group it was long (long-mixed). Subjects in the long-mixed condition acquired the heat-reinforced discrimination more rapidly than those in the short-mixed condition. These results suggest that the intermixed nature of stimulus exposure is an important determinant of the magnitude of perceptual learning effects.