Abstract
Visual search is frequently categorical, such as search for any member of the category ‘cup’. Categorical search templates must be formed from long-term knowledge based on exposure to category members. Recent work indicates that these templates are strongly biased toward recent experience. Specifically, feature regularities among recent exemplars from a category bias attention toward those features when searching for any category member. We hypothesized that a substantial portion of this effect derives from the last exemplar viewed. That is, we hypothesized that intertrial repetition effects can be category specific. Here, participants searched for an object cued by a category label (e.g., ‘cup’). Thirty-six categories were used, with one search trial per category in each of the 20 blocks. Target exemplars for each category appeared in one of two colors (e.g., cup targets were either grey or green, and car targets were red or white) and in one of two locations within the array. Target color and location within each category were randomly varied across blocks, creating four possible repetition conditions: color only, location only, both repeated, and neither repeated. Category repetitions were separated by an average of 36 trials, and thus any observed intertrial effects were necessarily based on retrieval from long-term memory. Both color and location repetition within a category facilitated visual search. In addition, these effects were broadly additive. Moreover, repetition effects were most pronounced in early blocks, with the effects decreasing across the experiment. In sum, the present results demonstrate 1) that intertrial effects are organized by object category, 2) that they can be based on retrieval from long-term memory, and 3), that they reflect both the properties of the most recently viewed exemplar and, because the effects diminished across the experiment, the accumulation of statistical regularities among multiple recent exemplars.