Psychophysical studies of short-term memory for attributes or dimensions of the visual stimulus known to be important in early visual processing--spatial frequency, orientation, contrast, motion--identify an early perceptual memory system. The proposed system, which may be part of the Schacter-Tulving perceptual representation system (PRS), is located early in the visual processing stream, prior to the structural description system responsible for shape priming but beyond primary visual cortex (V1), and consists of a series of parallel special-purpose perceptual mechanisms with independent but limited processing resources, where each mechanism is devoted to the analysis of a single stimulus dimension and is coupled to a memory store. The experimental evidence for this hypothesis is reviewed.