Bias Effects in Perceptual Identification: A Neuropsychological Investigation of the Role of Explicit Memory Margaret M. Keane Wellesley College; and Memory Disorders Research Center, Boston University School of Medicine and Boston Department of Veterans Affairs Medical Center Mieke Verfaellie Memory Disorders Research Center, Boston University School of Medicine and Boston Department of Veterans Affairs Medical Center John D. E. Gabrieli Stanford University and Bonnie M. Wong Memory Disorders Research Center, Boston University School of Medicine and Boston Department of Veterans Affairs Medical Center Identification of perceptually degraded words can be enhanced by prior exposure to those words. One theory proposes that such perceptual priming is due to a bias mechanism that induces costs as well as benefits in performance. Inherent in this theory is the critical assumption that bias effects observed in normal cognition reflect the operation of implicit rather than explicit memory processes. In the present study, we tested this assumption by examining the performance of amnesic patients in two paradigms that have elicited bias effects in normal participants. In Experiment 1, amnesic patients failed to show a normal bias pattern in a forced-choice perceptual identification paradigm, exhibiting benefits alone in perfor- mance. In Experiment 2, amnesic patients showed normal costs and benefits in a standard perceptual identification paradigm (without a forced-choice procedure). These results suggest that bias effects in normal cognition in the forced-choice perceptual identification paradigm are the product of explicit memory processes that are impaired in amnesia, but that bias effects in the standard paradigm are the product of implicit memory processes that are spared in amnesia. © 2000 Academic Press Key Words: priming; implicit memory; amnesia. Experience leaves its mark in a number of ways. Not only does it produce a memory trace that may be retrieved later at will, it also influ- ences subsequent behavior even in the absence of willful retrieval. In the laboratory, these two kinds of effects are measured in explicit and implicit memory tasks, respectively. In a typical explicit memory task, participants are exposed to a list of experimental stimuli in a “study” phase and are asked to recall or recognize those stimuli in a subsequent “test” phase. In an im- plicit memory task, participants are similarly exposed to a list of experimental stimuli in a study phase, but in the subsequent test phase This work was supported by a Science Scholar Fellowship from the Radcliffe Bunting Institute to Margaret M. Keane, and by grants NS26985 and MH57681. We are grateful to Melissa Zarella and Maria Chi for research assistance, to Shaun Cook for advice about statistical analyses, and to Mary Sue Weldon, Roger Ratcliff, and one anonymous reviewer for helpful comments on the manuscript. Correspondence concerning this article should be ad- dressed to Margaret M. Keane, Department of Psychology, Wellesley College, Wellesley, MA 02481. E-mail: mkeane@ wellesley.edu. 316 0749-596X/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved. Journal of Memory and Language 43, 316 –334 (2000) doi:10.1006/jmla.2000.2732, available online at http://www.idealibrary.com on