Perceptual learning in humans

Unsupervised exposure to confusable stimuli facilitates later discrimination between them. It is known that the schedule of exposure is critical to this perceptual learning effect, but several issues remain unresolved: I) it is not known whether a mechanism of mutual inhibition, taken by some to underpin perceptual learning in rats, is also evident in humans. II) Although simultaneous presentation of the to-be- discriminated stimuli has been suggested by some to be the most efficient way to promote perceptual learning, the associative mechanisms proposed by others (e.g., that of mutual inhibition) predict the opposite. Ill) Perceptual learning has been invoked as the process by which a face becomes familiar but surprisingly, this idea has received little empirical evaluation. The experimental work reported in this thesis addresses these three issues. Experiments 1 and 2, using flavours as stimuli, reveal that the inhibitory mechanisms that contribute to perceptual learning in rats also contribute to perceptual learning in humans. Experiments 3 and 4 demonstrate a perceptual learning effect using visual stimuli, pictures of human faces and that these effects too, exhibit parallels with studies of perceptual learning with rats. In particular they demonstrate that intermixed exposure results in greater perceptual learning than does blocked exposure. Experiments 5 to 7 indicate that perceptual learning seen following simultaneous exposure is, in turn, superior to intermixed exposure - implicating a process of stimulus comparison. Experiment 8 confirms that this novel effect is also observed with other visual stimuli, chequerboards, while those of Experiments 9 and 10 indicate that the face stimuli used exhibit some of the hallmarks of face processing. These findings establish, along with Experiments 3 to 6, that perceptual learning contributes to the process by which a face becomes familiar.