Retardation in human discrimination learning as a consequence of pre-exposure: Latent inhibition or negative priming?

A series of experiments with human subjects, using black-and-white chequerboard patterns, demonstrated that non-reinforced pre-exposure could impair performance in a subsequent learning task. Subjects were invited to take part in a scenario similar to that of a computer simulated card game. Their task was to turn over a series of cards by mouse-clicking on a pack of cards lying face-down, and then to classify these cards into one of two categories. In a subsequent task, subjects were asked to discriminate between pairs of chequerboards, some of which had previously appeared in the initial categorization phase: either directly ("fronts") or incidentally ("backs") involved in categorization. In Experiment 1, for those stimuli used as the backs of the cards (that is, those visible on top of the pack of cards), there was a significant impairment in performance relative to non-pre-exposed control stimuli. Although the impairment appeared to be specific to the stimuli pre-exposed, when the pre-exposed "backs" were minimally distorted in the discrimination task of Experiment 2, performance was still significantly impaired relative to non-pre-exposed control stimuli. The results of Experiment 2 do not support the interpretation that retardation in learning following masked pre-exposure in human experiments is comparable to latent inhibition following simple preexposure in other animals. Whilst the impairment in performance appears to be similar to that of latent inhibition, the results may instead, be better understood in terms of the inhibitory processes involved in negative priming. If this is so, then serious doubt is cast on whether latent inhibition has ever been reliably demonstrated in adult humans.