Benefits of Immediate Repetition Versus Long Study Presentation on Memory in Amnesia

Extensive research in individuals with intact memory shows that multiple study presentations lead to better recall and recognition performance than does a single study presentation. In an effort to elucidate the processes that mediate this repetition benefit, many studies have compared performance following massed (i.e., immediate) and spaced (i.e., distributed) repetitions. The typical finding is that spaced repetition is more beneficial than massed repetition, although massed repetition also yields better performance than does single presentation (Bird, Nicholson, & Ringer, 1978; Greene, 1989). Like individuals with intact memory, patients with selective amnesia show improved recognition memory following spaced repetition (Cermak, Verfaellie, Lanzoni, Mather, & Chase, 1996; Hillary et al., 2003; Verfaellie, Rajaram, Fossum, & Williams, 2008), and similar findings have been obtained in patients with severe memory impairments in the context of traumatic brain injury (Hillary et al., 2003) and Alzheimer’s disease (Moulin, Perfect, & Jones, 2000). However, in a study by Cermak et al. (1996), amnesic patients performed no better following massed repetition than following a single presentation on an immediate recall or recognition test – a finding that contrasts with the pattern seen in control subjects. This finding is surprising in light of the documented benefit associated with a single, long study presentation in patients with severe memory impairment. Indeed, a number of studies have successfully equated the recognition performance of amnesic patients and controls by providing amnesic patients with a single, long exposure duration and controls a single, short exposure duration (Hirst et al., 1986; Huppert & Piercy, 1978; Kopelman & Stanhope, 1998). One might expect that massed repetition and a single, long study presentation would be functionally equivalent. Although few studies have examined the effect of massed repetition on the performance of patients with memory impairment, there is evidence to suggest that the failure to benefit from massed repetition is not limited to patients with selective amnesia. Hillary and colleagues (2003) demonstrated a similar failure in patients with severe memory impairment secondary to moderate or severe traumatic brain injury. Thus, understanding the nature of the repetition impairment in patients with amnesia may elucidate memory impairments in other clinical groups as well. One reason for amnesics’ lack of benefit from massed repetition may be the failure to engage in further encoding when an item is immediately repeated. Deficient processing of massed items is also evident in individuals with intact memory, and has been postulated as one of the reasons as to why massed repetition leads to inferior memory than spaced repetition (Braun & Rubin, 1998; Greene, 1989). Nonetheless, in normal individuals, the second presentation of an item undergoes some further processing, as evidenced by the fact that performance exceeds that seen following a single presentation. In amnesic patients, in contrast, encoding may be even further curtailed, so that immediate repetition yields no processing benefit over a single presentation. Although the differential effects of massed repetition and long exposure duration in patients with severe memory impairment are potentially revealing, it is important to point out that these discrepant findings have been obtained in the context of distinct studies with different patient groups and different encoding parameters. Most importantly, the total presentation time employed in studies that have used a single, long presentation (Hirst et al., 1986; Huppert & Piercy, 1978; Kopelman & Stanhope, 1998) has typically been longer than that in studies that have used massed repetition (Cermak et al., 1996; Hillary et al., 2003). It is possible then that massed repetition may also enhance amnesic performance if the number of massed repetitions were extended to yield a total presentation time equivalent to that used in the long exposure studies. The goal of experiment 1 was to directly compare the repetition benefit associated with massed repetition and a single, long study presentation and to evaluate whether the magnitude of the repetition benefit in each of these conditions differed in amnesic patients and individuals with intact memory. To this end, we compared recognition memory in a single, short presentation condition with that in two ”extended exposure” conditions that were equated in terms of total study duration – a single, long presentation condition and a massed repetition condition.