Neuropsychology Copyright 2000 by the American Psychological Association, Inc. 2000, Vol. 14, No. 4, 570-578 0894-4105/00/$5.00 DOI: 10.1037//0894-4105.14.4.570 Intact Implicit Memory for Newly Formed Verbal Associations in Amnesic Patients Following Single Study Trials Yonatan Goshen-Gottstein Tel-Aviv University Morris Moscovitch and Brenda Melo University of Toronto and The Rotman Research Institute This study examines the ability of amnesic patients to recover newly formed associations implicitly after a single study trial. Fifteen amnesic patients with various etiologies studied pairs by forming a sentence containing both words. At test, all participants saw 40 intact pairs, 40 rearranged pairs, and 40 new words. All pairs appeared side by side both at study and at test. For the implicit lexical-decision task, 40 nonwords were intermixed with the other pairs, and participants indicated whether both items were words. For the explicit speeded- recognition test, participants were asked to indicate whether both words had appeared at study. Despite being severely impaired on the explicit test, amnesic patients performed like healthy controls on the implicit test, with faster and more accurate responses to intact pairs than to recombined pairs. Contrary to existing theories, the results suggest that amnesic patients can form and retain new associations. Global amnesia is characterized by an inability to remem- ber new episodes and facts accompanied by intact perfor- mance in other cognitive domains (Squire, 1992a, 1992b). The amnesic syndrome occurs as a consequence of bilateral damage to structures in the medial temporal lobe, dienceph- alon, or basal forebrain structures. The precise characteriza- tion of the functional deficit that underlies amnesia is the subject of ongoing debate and is the focus of this article. According to one suggestion, amnesia is best character- ized as a deficit in conscious recollection, as indexed by explicit tests of memory (for reviews, see Cohen & Eichen- baum, 1993; Moscovitch, 1982; Squire, 1992a, 1992b). According to this explicit-memory-deficit hypothesis, am- nesic patients are impaired on tests that require conscious recollection, such as recall and recognition. Performance is preserved, however, on implicit tests, in which a noncon- scious influence of past experience is found on current behavior, as indexed by measures such as repetition prim- ing, which is the difference in test performance between items (e.g., words, objects) that were presented in an earlier Yonatan Goshen-Gottstein, Department of Psychology, Tel- Aviv University, Ramat Aviv, Israel; Morris Moscovitch and Brenda Melo, Department of Psychology, University of Toronto, Toronto, Ontario, Canada, and the Rotman Research Institute, Toronto, Ontario, Canada. The results of this study were first reported at the annual meeting of the Society for Neuroscience, Washington, DC, No- vember 1995 (see Goshen-Gottstein & Moscovitch, 1995a). The project was supported by a grant from The Israel Foundation Trustees (1996-98) and by Natural Sciences and Engineering Research Council of Canada Grant A8347. We thank Marilyne Ziegler, Elzbieta Olzcewska, and Heidi Roessler for technical assistance. Correspondence concerning this article should be addressed to Yonatan Goshen-Gottstein, Department of Psychology, Tel-Aviv University, Ramat Aviv, 69978, Israel. Electronic mail may be sent to goshen@freud.tau.ac.il. study phase and baseline items that were not (Cermak, Talbot, Chandler, & Wolbarst, 1985; Diamond & Rozin, 1984; Graf, Squire, & Mandler, 1984; Rozin, 1976). A different characterization of amnesia suggests that not all forms of implicit memory are spared in amnesia (Squire, 1992b). Thus, whereas implicit memory is preserved for item-specific (nonrelational) information, it is impaired for association-specific (relational) information. According to this relational-deficit hypothesis, amnesic patients are im- paired in their ability to "relate or bind together into a compositional representation any set of perceptually distinct objects or events" (Cohen, Poldrack, & Eichenbaum, 1997, p. 135). Support for the hypothesis is based on converging evidence from neuroimaging (e.g., Cohen et al., 1994), functional neuroanatomy (for a comprehensive review, see Eichenbaum, Otto, & Cohen, 1992), and neurophysiology (e.g., Young, Fox, & Eichenbaum, 1994). The relational- deficit hypothesis predicts, therefore, that memory for rela- tional information should not be observed in amnesia, even when testing is implicit. The question of whether amnesic patients are able to display implicit memory for new associations is important not only for determining the functional deficit underlying amnesia but also for understanding the nature of the partic- ularly pronounced deficit found in remembering new asso- ciations (e.g., Shimamura & Squire, 1984). According to the relational-deficit hypothesis, the impairment results from an inability to form new associations in memory and, as such, reflects an encoding deficit that affects subsequent explicit as well as implicit tests. Alternatively, the explicit-memory- deficit hypothesis states that amnesic patients are able to form new associations but are unable to retrieve them con- sciously. According to this hypothesis, new associations cannot be retrieved on explicit tests, but they can be recov- ered on implicit tests. One way of distinguishing between the two hypotheses is to use a verbal paired-associate learning paradigm and test memory implicitly. To investigate implicit memory for 570