Retention Without Remembering

" Explicit measures of human memory, such as recall or recognition, reflect conscious recollection of the past. Implicit tests of retention measure transfer (or priming)from past experience on tasks that do not require conscious recollection of recent experiences for their performance. The article reviews research on the relation between explicit and implicit memory. The evidence points to substantial differences between standard explicit and implicit tests, because many variables create dissociations between these tests. For example, although pictures are remembered better than words on explicit tests, words produce more priming than do pictures on several implicit tests. These dissociations may implicate different memory systems that subserve distinct memorial functions, but the present argument is that many dissociations can be understood by appealing to general principles that apply to both explicit and implicit tests. Phenomena studied under the rubric of implicit memory may have important implications in many other fields, including social cognition, problem solving, and cognitive development. Remembering is "recalling to the mind" or "thinking of again," according to the American Heritage Dictionary. The definition implies that the rememberer is conscious (or aware) of both the current contents of mind and the fact that these represent recollections of the past. We generally think of remembering as potentially reflecting whatever we have learned, but a moment's reflection leads us to realize that this cannot be so. Humans learn many skills in which conscious remembering is unlikely to play much of a role, such as the sequences of finger movements involved in typewriting or tying one's shoes, the virtuoso performances of gymnasts or ice skaters, and many more mundane activities such as driving or shaving. People are unlikely to recall how to perform these skills; rather, when placed in the appropriate situation the person performs with little conscious awareness of how the behavior runs off (Kolers & Roediger, 1984). Indeed, as has often been remarked, when a person pauses to reflect on how a complicated skill is carried off, performance deteriorates. In some sense, these performances reflect prior learning but seem to resist conscious remembering. They are "unconscious," in the sense that their basis is difficult to describe in words. The study of unconscious learning has excited and plagued experimental psychology virtually throughout its history. To mention but a few prominent examples, the controversies surrounding perceptual defense (McGinnies, 1949), conditioning without awareness (Greenspoon, 1955), implicit learning of artificial grammars (Reber, 1967), and subliminal priming (Marcel, 1983) have occupied successive generations of researchers. In each case, the basic experimental phenomena have been called into question because of procedural problems, confounded factors, and the like. When these potential problems have been overcome and the phenomenon is more firmly established (e.g., Erdelyi, 1974), then usually its unconscious status is called into question (e.g., Dulany, Carlson, & Dewey, 1984; Holender, 1986). Despite these problems, the issue of unconscious or implicit learning has repeatedly been reintroduced into experimental psychology. The purpose of this article is to survey the most recent incarnation of this line of work, which is creating excitement in many circles. This article is organized into several sections. The first is an historical interlude about one origin of implicit memory research. The second section relates how the contemporary interest in implicit retention arose from neuropsychological studies of amnesic patients, and the third recounts how analogous implicit memory phenomena are studied in normal adult subjects. The fourth section outlines the two primary theoretical approaches to explaining implicit memory phenomena, and the fifth discusses research directed at testing between the theories. A sixth section discusses difficulties for the theories and challenges for the future. The last main section briefly discusses extensions of implicit memory work into other fields. The coverage in this article is necessarily somewhat selective. More thorough reviews of the implicit memory literature can be found in Richardson-Klavehn and Bjork (1988), Schacter (1987), and Shimamura (1986).