Visual marking of locations and feature maps: Evidence from within-dimension defined conjunctions

Recently, Watson and Humphreys (1997, 1998) proposed that the selection of new visual events can be aided by the top-down inhibition of old information-visual marking (VM)-and that the mechanisms of marking differ for static and moving stimuli. Stationary stimuli are marked by location-based inhibition, whereas moving stimuli are marked by inhibition applied at the level of whole-feature maps. Here we provide a test of this "two-mechanism" account. We show that static items can be marked even when old and new stimuli contain the same features and so cannot be distinguished by activation within a unique feature map. However, moving old items could not be marked unless they possessed a unique feature (colour). Manipulations of grouping strength, both within and between distracter sets, did not affect the basic findings. The results support the existence of two mechanisms for VM and counter an object-based inhibition explanation of performance.