The “Memory System” of Prelinguistic Infants a

With the exception of some isolated studies in the first half of this century (e.g., Jones, 1930), the study of memory in infants, both animal and human, is a relatively recent pursuit. Although psychologists of many persuasions, ranging from Freud to Watson, attached considerable theoretical importance to the long-term effects of infants’ early experiences, few attempted to document whether or not these experiences actually influenced behavior later in development. Indeed, evidence from three different lines of research on infantile memory suggested that they did not. First, research with children and adults consistently indicated that their earliest memories dated from the ages of 2-5 years (Campbell & Coulter, 1976; Wetzler & Sweeney, 1986). Second, conditioning studies with infants consistently yielded no evidence of learning when the interval between the CS and US (classical conditioning) or between the response and the reinforcement (operant conditioning) exceeded 2-3 sec (Lipsitt, this volume; Little, Lipsitt & Rovee-Collier, 1984; Millar, this volume; Millar & Watson, 1979), or when the interval between successive response-reinforcement repetitions exceeded 5-7 sec (Watson, 1972). Because two events cannot be associated unless the memory of the first event persists until the second event has occurred (Bolles, 1976; Revusky, 1971; Watson, 1984), these data suggested that the memorial abilities of infants were limited at best. Third, studies of novelty detection following habituation to a standard stimulus yielded no evidence of retention after delays exceeding 5-15 sec by infants younger than 1 year (Sherman, 1985; Stinson, 1971; Werner & Perlmutter, 1979). Taken together, these findings led to the general conclusion that the prelinguistic infant was incapable of storing memories over the long term (Kagan, 1984). In recent years, evidence has accumulated that prelinguistic infants can retain information about the events in which they participated for periods of weeks and even months (see Rovee-Collier & Hayne, 1987, for review; Myers, Clifton & Clarkson, 1987; Perris, Myers & Clifton, in press). The disparity between these and earlier findings has been attributed by many researchers to the functioning of different types of memory systems. The terms used to capture the distinction between these 2 types of memory systems have included earlyand late-maturing (Bachvalier & Mishkin, 1984; Schacter & Moscovitch, 1984), implicit and explicit (Schacter, 1987), procedural and declarative (Squire, 1986, 1987), semantic and