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Set-shifting refers to a process of cognitive control which is shown through flexible behavioural adaptation to changes in task parameters or demands, such as the switching of an explicit rule (extra-dimensional rule shifting) or the reversal of a reinforcement-contingency (reversal-learning). Set-shifting deficits are widely documented in specific neuropsychological disorders, but seldom investigated in relation to normally-occurring individual differences. In a sample of healthy adults (N=78, 28% male), we demonstrate that Working Memory and trait Psychoticism have independent involvement in extra-dimensional rule shifting as measured using an analogue of the Wisconsin Card Sorting Test. Only Psychoticism, however, was involved in reversal-learning, as assessed using a recent modification of the Iowa Gambling Task. Individual differences in extra-dimensional rule shifting were explained in terms of rule abstraction speed, while individual differences in reversal-learning were explained in terms of response perseveration. These results clarify component processes in different forms of set-shifting, and highlight the role of individual differences, especially personality, in cognitive control.

International audienceConsideration is given to the tasks that make judgements of colour similarity based on perceptual similarity rather than categorical similarity. Irrespective of whether colour categories are taken to be universal (Berlin & Kay, 1969) or language induced (Davidoff, Davies, & Roberson, 1999), it is widely assumed that colour boundaries, and hence categorical similarity, would be used when categorising colours. However, we argue that categorical similarity is more reliably used in implicit than in explicit categorisation. Thus, in Experiment 1, we found that category boundaries may be overridden in the explicit task of matching-to-sample: There was a similar strong tendency to ignore colour boundaries and to divide the range of coloured stimuli into two equal groups in both Westerners and in a remote population (Himba). In Experiment 2, we showed that a distinctive stimulus (focal colour) in the range affected the equal division in a matching-to-sample task. Experiment 3 tested the stability of a category boundary in an implicit task (visual search) that assessed categorical perception; only for this task was categorisation largely immune to range effects and largely based on categorical similarity. It is concluded that, even after colour categories are acquired, perceptual rather than categorical similarity is commonly used in judgements of colour similarity

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