We investigated the mechanisms by which concepts are learned from examples by manipulating the presentation order in which the examples were presented to subjects. We introduce the idea of a rule-based presentation order, which is a sequence that respects the internal organization of the examples within a category. We find that such an order substantially facilitates learning, as compared with previously known beneficial orders, such as a similarity-based order. We discuss this result in light of the central distinction between rule-based and similarity-based learning models.
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A number of studies have investigated whether category learning is influenced by the order in which examples are presented. Elio and Anderson (1981) found that categories are learned faster when training is blocked into groups of mutually similar examples (see also Elio & Anderson, 1984). More recently, Medin and Bettger (1994) demonstrated a strong learning advantage when training objects were presented in an order that tended to maximize similarity between successive examples. Other studies, such as those of Clapper and Bower (1994) and Goldstone (1996), have focused on the effect of alternation of contrasting categories. Presentation order effects are especially interesting in the light of categorization models that emphasize incremental learning from trial to trial. For example, Sakamoto, Jones, and Love (2008) showed that order can affect the incremental update of both category means and variances (see also Love, Medin, & Gureckis, 2004). Incremental-learning models are naturally susceptible to order effects, whereas other models may be less so, so the manipulation of presentation order is a potentially useful tool for studying the mechanisms of learning.
However, previous studies of presentation order were limited in that they used orders based on simple similarity-for example, maximizing or minimizing the similarity between adjacent training examples. Here, we explore a type of presentation order that depends in a more structured way on the nature of the category to be learned. We introduce the notion of a rule-based presentation order, which is one that derives from the internal structure of the training examples. In our rule-based order, objects that are within a rule-that is, that obey the same structured subclass within the category-are presented adjacently in the presentation sequence. Training then moves on to another subclass, and so forth until all the objects have been presented. (Negative instances are randomly interspersed among the positives; only the order of the positives is manipulated.) Below, we will compare subjects' performance with such an order with the similarity-based order found to be advantageous in earlier studies. For comparison, we will also include a dissimilarity-based order, previously found to be disadvantageous. We hypothesize that the rulebased order will facilitate learning, particularly in highly structured concepts (i.e., those containing more clusters), by aiding the subject in mentally organizing what would otherwise appear heterogeneous or chaotic.
The subjects were 96 Rutgers University students who received course credit in exchange for their participation.
Tasks were computer-driven. The subjects learned to sort stimulus objects using two keys, with successful learning encouraged by means of a progress bar. Stimulus objects were presented one at a time in the upper part of the computer screen. After each response, feedback indicating a correct or incorrect classification was provided at the bottom of the screen for 2 sec. The subjects learned a simple concept in two dimensions as a short warm-up session. Then each subject was asked to learn the two chosen concepts (details below). The order of the two concepts was counterbalanced between subjects. For each subject, a single presentation order was randomly chosen and applied to the two concepts. …