Tests for implicit memory have been pursued extensively for about two decades, and the findings from such memory experiments are commonly considered to have confirmed the phenomenon of implicit memory. Schacter (1987) defined “implicit memory” as facilitation of task performance because of prior experience, in the absence of conscious or intentional recollection (explicit memory). That rather broad definition might seem to encompass the definitions of implicit learning, conditioned learning, motor-skills learning, and perceptual adaptation (Roediger and McDermott, 1993), but will not be considered to do so here. Instead, our focus will be on the branch of implicit memory known as repetition priming. In our terminology, repetition priming is tested when the stimuli presented are the same (identical) or of the same type (essentially the same, but varying in some way) at priming and at testing. In this type of experiment, the response to a repeated stimulus is facilitated without the influence of explicit memory from the first encounter.
Implicit memory can also be measured using cross-modal priming, where the sensory modalities used differ between priming and testing. This review will cover cases of cross-modal priming in which odor names are presented at priming, and odors at testing. Several recent studies have examined cross-modal priming using the olfactory and visual modalities, assessing the influence of processing an odor on the later processing of a visual stimulus (e.g., Hermans, Baeyens, and Eelen, 1998; Grigor et al., 1999; Pauli et al., 1999; Sarfarazi et al., 1999).