Academic journal article Canadian Journal of Experimental Psychology

Encoding Conditions and the List-Strength Effect

Academic journal article Canadian Journal of Experimental Psychology

Encoding Conditions and the List-Strength Effect

Article excerpt

Abstract The list - strength effect occurs when "strong" items within a list are remembered at the expense of "weak" items within that same list. The results of two experiments showed that variably encoded words were remembered better than words repeated with the same encoding context, whether memory was measured by free recall, frequency estimates, or recognition d'. However, there was little or no evidence from any of the measures that the variably encoded words were recollected in the mixed lists at the expense of the similarly encoded words. This pattern held even though, in Experiment 2, there was a list - strength effect on free recall, when list strength was manipulated by increasing the number of presentations of a word. It was concluded that the free recall results could not be accommodated by the model of memory postulated by Shiffrin, Ratcliff, and Clark (1990) to account for the effects of list strength.

Variability of Encoding and the List - Strength Effect In the past 5 years a number of studies have been carried out to investigate the list - strength effect, a term coined by Ratcliff, Clark, and Shiffrin (1990). The basic paradigm requires that "strong" items and "weak" items be presented in "pure" lists (i.e., lists including only strong or weak items respectively) and in "mixed" lists (which contain both strong and weak items). Items are judged to be strong or weak if recollection of the strong items is consistently and significantly better than recollection of the weak items. Typically, some items are strengthened by repeating them or giving them additional processing time relative to other items.

A strong version of the list - strength effect states that the strong items are recollected at the expense of the weak, when both types occur in the same list. In other words, strong items are recollected better from a mixed list than from a pure list while the opposite holds for weak items. A weaker version of the effect simply states that the difference in recollection between strong and weak items is greater within a mixed list than between pure lists. Ratcliff et al. (1990) tested primarily for the presence of this weaker version, comparing the strong: weak performances as a ratio.

Tulving and Hastie (1972) provided an early, partial demonstration of the list - strength effect. They gave subjects one of three types of lists to learn and recall:A+B, A+B+C, A+B+B, where A, B, and C are sets of words within a list. They found that, for the A+B+B list, recall of the B words was enhanced and recall of the A words was lowered compared to the recall of these words from either of the other two lists. This effect was replicated by Hastie (1975) for free recall but not for recognition. These experiments, though, did not test whether recall of strong items was enhanced by virtue of their presence in a mixed list, because they did not have a pure strong condition. However, Ratcliff et al. (1990, Experiments 4 and 6) did find that recall of the strong items was generally enhanced in mixed conditions (and recall of the weak items was generally inhibited).

Most of the more recent studies of the phenomenon have measured memory with recognition (e.g., Murnane & Shiffrin, 1991b; Ratcliff et al., 1990; Yonelinas, Hockley, & Murdock, 1992). Generally speaking, the results have replicated those of Hastie (1975); i.e., they showed no effects of relative list strength when memory was measured by recognition. Shiffrin, Ratcliff, and Clark (1990) have argued that most current models of recognition have difficulty accounting simultaneously for the presence of a list - length effect on recognition (i.e., a decrease in recognition performance as the number of items in a list increases) and an absence of a list - strength effect, although this argument is open to debate (see Murdock & Kahana, 1993.) This theoretical argument seems to be the main reason for the current emphasis on recognition in studies of the list - strength effect. …

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