Wanted: a new psychology of exemplars.

Abstract Present-day exemplar theory faces difficult challenges, and important questions have arisen about the kinds of exemplar effects and processes that are empirically supported, and about the kind of exemplar theory that could still be constructive. One question concerns whether exemplar generalization in memory and categorization is broad and collective - extending to many related exemplars stored in memory - or whether it is focused and singular extending only to highly similar (nearly identical) exemplars. The present article considers this continuum from broad to narrow generalization. I demonstrate that in prominent memory and category tasks - tasks in which exemplar theory predicts broad generalization - generalization is in psychological reality very tightly focused. These demonstrations could ground a new, productive exemplar theory that is true to psychological process as humans conduct themselves in memory and category tasks. This new psychology may actually reprise the traditional exemplar theory that predated our sophisticated, mathematical exemplar models. Categorization is a central issue in cognitive science. Beginning with influential statements by Brooks (1978) and Medin and Schaffer (1978), instance or exemplar theory assumed a prominent position in explaining human categorization. Exemplar theory assumes that . we store the category members we experience as individuated memory representations. Then, when a to-be-categorized item (TBCI) comes along, we judge whether it belongs to a category by considering its similarity to those stored exemplars. Initially, formal treatments of exemplar theory enjoyed success in the literature (Nosofsky, 198(5). Recently, though, exemplar theory has been shown to have serious flaws and to fail qualitatively at critical points (Ashby & Alfonso-Reese, 1995; Ashby, Maddox, & Lee, 1994; Blair & Homa, 2001; Cutting, Bruno, Brady, & Moore, 1992; Maddox & Ashby, 1998; Myung & Pitt, 1997; Smith, 2002; Smith & Minda, 1998, 2000, 2001, 2002; Smith, Murray, & Minda, 1997). Thus, important questions arise about the status of exemplar theory, about the kinds of exemplar effects and processes that are supported empirically, and about the kind of exemplar theory that could still be constructive. I consider these questions in this article. Considering them will lead me back to the original exemplar principle expressed in Brooks (1978) that remains one of the best statements about the psychology of exemplars. Once in the Alps, I was walking down a steep trail that I had walked years before. I was rehabilitating a knee and the doctor had told me that I could walk but must not fall. On I came, and it began to sprinkle rain. Suddenly the hackles stood up on my neck, and I knew I was coming to a place in the trail where I could fall. Fair warning, because a few seconds later - boom - down I went. What happened psychologically in the moment of my self-warning? What connections did my mind draw from the present situation to things it knew or had experienced? Was this a phenomenon of memory or categorization? What theory would describe it? A constructive way to frame these issues and this article is to contrast two psychological descriptions of what happened that day. First, my situation that day might have connected to many stored experiences of steep, rocky, or rainy trails. I might have summed up the similarities between the situation and those experiences and judged that there was enough steep-wet-rock-fall similarity to give myself a warning. By this description, I would have used diverse exemplar experiences in concert to produce my cognitive assessment. This is one way - a broad, collective way - in which we might use exemplar experience. This is one kind of exemplar theory. Second, my situation that day might have connected only to the single time I negotiated that bad step on that trail before. In this case, a connection would have been drawn from one precise context to another highly similar (nearly identical) context - one to one, match and warn. …