Short-Term Recall of Order Information: Influence of Encoding and Generation Processes on Distinctiveness, Isolation, and Background Effects

Article excerpt

We examined the influence of encoding and generation processes on distinctiveness, isolation, and background effects in short-term recall of order information. Adults recalled the order of letters in one of two segments following a distractor task, knowing in advance the identity of the letters. A distinctive letter was one that was either in red or absent and replaced with a red dash, thereby requiring generation. On trials with a distinctive letter, the letter was primed in advance. A negative generation effect was found; in addition, there was a positive distinctiveness effect but a negative background effect on trials in which generation was required. These effects can be explained in terms of the extra processing given to distinctive items when they need to be generated.

That there is superior long-term memory for a distinctive or isolated item in a list has been supported by much research (von Restorff, 1933; see Schmidt, 1991, for a review). However, the effects of distinctiveness or isolation on short-term memory and on memory for order information are more controversial (see, e.g., Kelley & Nairne, 2001). Some confusion about the effects of distinctiveness may arise because there are different ways to examine such effects. To understand these differences, let us consider trials in which a distinctive item is embedded within a list of nondistinctive items. Such experimental trials can be contrasted with control trials containing no distinctive items. A common way to assess the effects of distinctiveness is to compare a distinctive item on an experimental trial with a comparable item on a control trial. We refer to this measure as an assessment of the isolation effect. Alternatively, as in recent studies by Cunningham, Marmie, and Healy (1998) and Healy, Cunningham, and Parker (2002), as well as in the classic study by von Restorff, distinctiveness can be assessed by comparing a distinctive item on an experimental trial with the nondistinctive items on the same trial. We refer to this measure as an assessment of the distinctiveness effect. In a related assessment, which we refer to as an evaluation of the background effect, the nondistinctive items on an experimental trial would be compared with the comparable items on a control trial. In the present study, we separately evaluate all three of these effects under two related conditions: a generate condition, in which the distinctive item is not presented and must be produced by the participant, and a read condition, in which the distinctive item is presented and must only be read by the participant. Kelley and Nairne specifically noted the need to disentangle the effects of generation and isolation, which in previous studies have been confounded.

This study follows two recent studies in which recall of distinctive items was examined (Cunningham et al., 1998; Healy et al., 2002), in which distinctiveness was defined as changing the characteristics of an item to make it qualitatively different from other items in a list. In these studies, a manipulation of distinctiveness stronger than the usual ones (e.g., those in which the distinctive item is a different color from the other items) was used, because an item was made distinctive by deleting it from a known list of items and replacing it with a red dash. The overall methodology in these studies consisted of (1) a distractor paradigm (in which the to-be-recalled items were letters, and the distractor task required reading digits aloud), (2) a partial-report procedure (in which a list of eight letters presented on a trial was divided into two four-letter segments, with only one segment cued for recall), and (3) a reconstruction procedure (in which the letters used were held constant across trials and, thus, were known by the participants, so that their task was solely to reproduce the order of those letters). Specifically, the participants received two segments of letters and recalled the order of one segment after a digit-filled retention interval. …


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