Academic journal article Memory & Cognition

Primacy or Recency Effects in Forming Inductive Categories

Academic journal article Memory & Cognition

Primacy or Recency Effects in Forming Inductive Categories

Article excerpt

Five experiments provide evidence for a primacy effect in the formation of inductive categories. Participants completed a category induction task in which they observed and reproduced a set of lines that varied in length but were serially ordered so that they increased or decreased in length. Subsequent estimates of the average of the distribution were systematically biased in the direction of stimuli encountered at the beginning of the induction task, suggesting that initially encountered stimuli exert greater weight in a category representation than do subsequent stimuli. We offer possible explanations for why this primacy effect might arise.

Since Ebbinghaus's (1885/1913) classic study on memory, psychologists have systematically explored serial position effects across a variety of domains in memory and cognition. The majority of these studies have been concerned with the relative salience or retention of information encountered early (primacy effect) versus later (recency effect) in a sequence. Although there is a large body of literature on serial position effects in memory recall (e.g., Gershberg & Shimamura, 1994; Howard & Kahana, 1999), relatively little research has explored primacy or recency effects in inductive categories that are formed through experience with a distribution of category instances. Since such categories are generally established by encountering stimuli over the course of time, it is possible that the temporal or sequential order in which people experience a distribution of stimuli influences the underlying representation. This article addresses the question of whether stimuli encountered when one initially forms an inductive category are allocated greater weight in the representation than are subsequent stimuli by exploring retrospective judgments about the distribution of stimuli consisting of lines that varied in length but are not randomly drawn from a distribution.

Inductive Categories

Inductive categories are established through experience with an observed distribution of stimuli (Duffy, Huttenlocher, & Crawford, 2006; Huttenlocher, Hedges, & Vevea, 2000). Typically, such categories exhibit a graded structure, with category instances varying in magnitude or value along some relevant stimulus dimension. For example, one could travel to a city such as Philadelphia and, on the basis of experience with the particular individuals encountered during the trip, form a category of Philadelphians that includes distributional information, such as their typical height or intelligence, as well as extreme values of the category, such as the most helpful or least helpful Philadelphia!!, and so on. Such categories can be described statistically as a bounded range along a stimulus dimension having a central prototypic value that can be instantiated as the average value of all the experienced instances (Duffy, Huttenlocher, Hedges, & Crawford, 2007).1 Later, one might be asked to report the prototypic value of the category or even its boundaries.

A variety of experimental studies have addressed how people form inductive categories from experience with stimuli that vary along one or more feature dimensions (Duffy & Kitayama, 2007; Flannagan, Fried, & Holyoak, 1986; Fried & Holyoak, 1984; Huttenlocher et al., 2000; Posner & Keele, 1968). In many of the tasks employed in these studies, participants have learned a new category by observing and making judgments about a series of category instances consisting of stimuli that varied along some dimension, such as square grid patterns presented as works of abstract art (Fried & Holyoak, 1984), dot patterns of geometric figures that varied in degree of distortion (Posner & Keele, 1968), blood cells that varied in size (Duffy & Kitayama, 2007), or lines that varied in length (Huttenlocher et al., 2000). After category induction, die participants have been tested on whether they learned the category by having them classify novel instances as to their category membership. …

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