Abstract
Duncan and Humphreys (1989) proposed that search efficiency decreases as target-distractor similarity increases. The items that best resemble the target are grouped together, whereas the items that do not resemble the target are grouped together, and discarded. Search is then based only on the items that received the most activation. According to Ariely (2001) perceptual averaging (i.e., the ability of observers to represent sets of similar objects by their overall statistical properties, rather than their individual properties) could possibly facilitate this grouping process (see also Rosenholtz, 1999). In the present set of studies we used a series of conjunction search tasks to demonstrate that size averaging operates to improve the efficiency of search among items varying in size when size is both a) relevant to the search task (localize a target circle, defined by a color/size conjunction, Experiments 1 and 2) and b) irrelevant to the search task (localize a target line, defined by a color/orientation conjunction, Experiment 3 and 4). Results showed that search for a target was slower when target size corresponded to the average size of the distractors than when it did not (Experiment 1); that search was slower when target size corresponded to the average size of distractors appearing in the same color as the target than when it did not (Experiment 2); and that search was less efficient when target size corresponded to the average size of distractors appearing in the same color as the target than when it did not, even though target size was not a relevant search criterion (Experiments 3 and 4). These results emphasize the role of perceptual averaging in visual search among items varying in size, suggesting that targets are located first by segregating items into perceptual groups (by color) and then by isolating possible targets from distractors by size.
This work was supported a by Natural Sciences and Engineering Research Council of Canada Discovery grant, awarded to the second author.