Visual Search for Conjunctions of Motion and Form: The Efficiency of Attention to Static versus Moving Items Depends on Practice

Abstract

Visual search for some motion-form conjunctions can be performed in parallel. Yet, if the target is easy to discriminate from the nontargets (target line tilted 45 from the vertical), search can be easier for a moving than for a stationary target. Driver and McLeod (1992; Berger & McLeod, 1996) took this asymmetry to argue that gross aspects of form discrimination are performed within a motion filter thatrepresents only the moving items, whereas discrimination of stationary items (and all fine discrimination) relies on a static form system. However, recent (unsuccessful) attempts to replicate the asymmetry (Muller & Found, 1996; Muller & Maxwell, 1994) suggested that it may occur only early during task performance, due to participants having difficulty keeping the moving items out of the search for a stationary target (but not vice versa). This was confirmed by the present study, which investigated the effects of practice on search among the moving and stationary subset of items. The results suggest that attention to the stationary subsetis difficultinitially because participants cannotefficiently compensate for the natural bias of the motion filter to pass the moving items (rather than filter them out). This ability improves with practice. Thus, there is no fixed limit to performance with stationary targets and, consequently, no need to assume that any form discrimination is performed within the motion filter.