Repetition effects of features and spatial position: evidence for dissociable mechanisms.

While repetition of a feature (position) unrelated to a response is acknowledged to be facilitatory, there is disagreement on whether priming for response-defining feature or spatial position is facilitatory or inhibitory. To address this question, we used simple feature targets to analyze the interactions between facilitatory and inhibitory mechanisms associated to the repetition of features and position, for responses given either to the feature or to the position. We were able to reproduce the general facilitatory effect when a feature was repeated, and the inhibitory effect when it was changed, although these feature priming effects were always in interaction with repetition effects of spatial position. The most interesting finding, however, was that repetition of spatial position showed facilitation when non-response-defining, and inhibition when coincident with the response (response-defining); that is, repetition effects of spatial position are strictly dependent on the object of the motor response (a feature vs the position itself), whereas repetition priming for features is not, suggesting the involvement of a different mechanism and different neural substrate in the two cases. These effects interact, resulting in an ecologically plausible heuristic of visual discrimination that facilitates recently viewed features appearing in recently visited positions, but inhibits recently visited positions containing features recently associated with a distractor.