Recent data from brain-damaged and normal subjects converge to suggest several characteristics of repetition priming: firstly, it is sensitive to the physical and structural properties of input; secondly, it is unaffected by semantic processing at encoding; thirdly, it is frequently preserved in amnesic patients with impaired explicit memory; fourthly, it depends upon perceptual representations processed and stored by modality-specific cortical memory systems; and, finally, it is subject to constraints particular to the task employed and the type of information that is primed.