Superior discrimination between similar stimuli after simultaneous exposure

Abstract

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.

Keywords:

• Perceptual learning
• Stimulus discrimination
• Human
• Chequerboards
• Faces

Acknowledgments

This research was funded by an Economic and Social Research Council grant (to D.M.D.), a Medical Research Council studentship (to M.E.M.), and a Biotechnology and Biological Sciences Research Council grant (to R.C.H.).

Notes

¹ It should be noted that Mundy et al. (2007) provide evidence for the formation of an excitatory association during simultaneous exposure to highly discriminable stimuli (see their Experiment 5). Thus our results do not challenge the basic idea that simultaneous exposure establishes an excitatory association between simultaneously presented stimuli. Instead, they indicate that the excitatory association must be counteracted by some other mechanism.

² The fact that there are two different stimuli presented on simultaneous trials (AX–BX/BX–AX) and two copies of the same stimulus presented on successive trials (CY–CY/DY–DY) might affect the amount of attention paid to the stimuli. This matter is discussed in depth in Mundy et al. (2007).