Perceptual learning in humans: roles of preexposure schedule, feedback, and discrimination assay.

In three experiments, humans received preexposure to two compound flavours (AX and BX: saline-lemon and sucrose-lemon) that were presented either in an intermixed (e.g., AX, BX,...BX, AX,...) or a blocked (e.g., AX, AX,...BX, BX...) fashion. Subsequently, AX was paired with an unpleasant bitter taste, and the discriminability of AX and BX was assessed using the accuracy of same/different judgements and by the extent to which any learned dislike of AX generalized to BX. When participants received feedback about the accuracy of their same/different judgements during preexposure those given intermixed preexposure were more accurate in making these judgements during the test than those given blocked preexposure (Experiments 1 and 2A), however, there was no evidence of any learned dislike in these experiments. In Experiment 2B, in which participants did not receive feedback about the accuracy of their judgements, there was no effect of the preexposure regime on same/different judgements, but there was a learned dislike of AX, and this generalized less to BX in participants given intermixed than in those given blocked preexposure. The beneficial effects of intermixed preexposure are consistent with results from other species (chicks and rats), but the differences created by the presence or absence of feedback place constraints on the analysis of these effects.

Representational blending in human conditional learning: Implications for associative theory.

In two experiments, participants were presented with pictures of different foods (A, B, C, D, X,) and learned which combinations resulted in an allergic reaction in a fictitious patient, Mr X. In Problem 1, when A or B (but not C or D) was combined with food X an allergic reaction occurred, and when C or D (but not A or B) was combined with Y an allergic reaction occurred. In Experiment 1, participants also received Problem 2 in which A, B, C, and D interacted with foods V and W either in the same way as X and Y, respectively, or in a different way. Participants performed more proficiently in the former than in the latter condition. In Experiment 2, after training on Problem 1, participants judged whether or not novel combinations of foods (e.g., AB, CD, AD, CB) would cause an allergic reaction in Mr X. They were no more likely to indicate that AB or CD would cause an allergic reaction than AD or CB, but made their judgements more rapidly and with greater confidence on AB and CD trials than on AD and CB trials. These results (1) indicate that shared representations come to be addressed by the components of similar compounds (e.g., AX and BX) that have predicted the same outcome (an allergic reaction), and (2) are inconsistent with standard, associative theories of learning, but (3) are consistent with findings from nonhuman animals and with a connectionist interpretation of these findings.