Perceptual implicit memory for previously attended and unattended words was measured either in a word-stem completion task or in a perceptual fluency (perceptual identification) task Subjects (N = 144) first engaged in a focused attention task in which they were to identify one of two words presented for 100, 200, or 300 msec. Words were classified as attended if they were reported during the focused attention task and unattended if they were not. Results for both implicit memory tests indicated reliable perceptual implicit memory for attended words but not for unattended words, regardless of focused attention exposure duration. The results indicate that perceptual implicit memory tasks reflect attentional encoding processes; that is, words must undergo attentional encoding if they are to affect performance on a later perceptual implicit memory test.Implicit memory is the phenomenon in which previously encoded information affects performance on some task without the individual's consciously recollecting the information. This nonconscious, automatic retrieval contrasts with the conscious, effortful retrieval that occurs during an explicit memory test such as recognition or recall. A number of different implicit memory tests have been identified, and they have been classified into two broad categories: conceptual and perceptual. Category exemplar production, general knowledge tests, and spelling tasks are considered to be conceptual implicit memory tests; perceptual fluency (also termed perceptual identification), word-stem completion, and word-fragment completion are considered to be perceptual implicit memory tests (e.g., Roediger, 1990;Roediger, Weldon, & Challis, 1989). Conceptual implicit memory tests often are affected by encoding variables that affect explicit memory tests, whereas perceptual implicit memory tests are not affected by these variables.Attentional processing at encoding is assumed to be necessary to produce explicit memory for the encoded information (see, e.g., Fisk & Schneider, 1984;Rock & Gutman, 1981;Shiffrin & Schneider, 1977). The necessity of attentional processing at encoding also has been demonstrated for conceptual implicit memory tests (e.g., Mulligan, 1998;Mulligan & Hartman, 1996). It has beenThe 100-msec conditions of this study were presented at the April, 1996, meeting of the Iowa Academy of Science, and the entire study was presented at the May, 1997, meeting of the Midwestern Psychological Association. We thank Nelson Cowan, William Johnston, and Neil Mulligan for helpful comments on an earlier version of this paper. We also thank Elizabeth Andre, Alison Bateson, Kelli Bendickson, Karla Benson, Katie Bock, Amanda Easton, Dana Hartwigsen, Brenda Jacobus, Patricia Schmidt, Molly White, and Steve Willis for their assistance in collecting the data. Correspondence concerning this article may be addressed to either author at the Department of Psychology, Iowa State University, Ames, IA 50011-3180 (e-mail: bcrabb@iastate. edu or vjdark@iastate.edu).argued, however, that whereas atte...
