Superior discrimination between similar stimuli after simultaneous exposure.

Human participants received unsupervised exposure to difficult-to-discriminate chequerboard stimuli (e.g., AX and BX), before learning a discrimination between them. Experiment 1 demonstrated that prior exposure enhanced later discrimination and that intermixed exposure (AX, BX, AX, BX ...) resulted in better subsequent discrimination than did blocked exposure (CY, CY ... DY, DY ...). Experiment 2 showed that simultaneous exposure to two similar stimuli (AX-BX, BX-AX ...) facilitated the later acquisition of a successive discrimination, more than successive exposure (AX-AX, BX-BX ...). These results parallel those observed by Mundy, Honey, and Dwyer (2007) who used pictures of human faces as stimuli and establish the generality of the fact that simultaneous exposure produces a particularly marked perceptual learning effect.