Implicit visual working memory.

Psychophysical studies of the short-term memory for attributes or dimensions of the visual stimulus that are important in online perceptual processing of visual images - spatial frequency, orientation, contrast, motion - identify a low-level perceptual memory mechanism. This mechanism is located early in the visual processing stream, prior to the structural description system, but beyond the primary visual cortex (V1); it is composed of a series of parallel, special-purpose perceptual mechanisms with independent but limited processing resources. Each mechanism is dedicated to the analysis of a single attribute or dimension of the visual stimulus, and is coupled to a memory store. The evidence for this model from psychophysical and recent functional brain imaging studies is reviewed.