Academic journal article Attention, Perception and Psychophysics

Objects with Reduced Visibility Still Contribute to Size Averaging

Academic journal article Attention, Perception and Psychophysics

Objects with Reduced Visibility Still Contribute to Size Averaging

Article excerpt

People can rapidly judge the average size of a collection of objects with considerable accuracy. In this study, we tested whether this size-averaging process relies on relatively early object representations or on later object representations that have undergone iterative processing. We asked participants to judge the average size of a set of circles and, in some conditions, presented two additional circles that were either smaller or larger than the average. The additional circles were surrounded by four-dot masks that either lingered longer than the circle array, preventing further processing with object substitution masking (OSM), or disappeared simultaneously with the circle array, allowing the circle representation to reach later visual processing stages. Surprisingly, estimation of average circle size was modulated by both visible circles and circles whose visibility was impaired by OSM. There was also no correlation across participants between the influence of the masked circles and susceptibility to OSM. These findings suggest that relatively early representations of objects can contribute to the size-averaging process despite their reduced visibility.

The world presents the visual system with an enormous amount of information. Many types of visual operations can be overwhelmed, becoming less efficient or less precise if processing is too distributed in scope. Efficiently recovering information often requires focused processing on only a few objects. Yet, even when this scope is distributed to include larger numbers of objects, information about the features and identities of the collection is often still available. Past research suggests that this feeling may be supported by access to statistical summaries of object features, even when precise information about individual objects is not accessible (Ariely, 2001). Much of this research focuses on the feature of object size. In one study, participants viewed a briefly presented display of heterogeneously sized circles and then judged whether a subsequent test circle was present in the first display. The participants were poor at distinguishing circles that were present in the first display from those not present, suggesting that they stored little information about individual objects. But the participants knew the boundaries of the range of possible sizes in the first display and were accurate at rejecting test circles that were outside of this range. A separate experiment showed that even without knowledge of the sizes of individual objects, the participants did have access to the average circle size. Estimates differed from the actual average size of the set by only 4%-12%.

In another series of studies, estimates of average size were actually more accurate when attention was broadly distributed over multiple objects relative to when individual objects were inspected serially (Chong & Treisman, 2005a). Participants saw a brief display of heterogeneously sized circles, and their task was either to estimate the average size of all circles or to report the size of a single object cued after the disappearance of the display. In both cases, the participants performed a secondary task to manipulate whether their region of selection was focused or distributed. In the focused manipulation, the participants either performed a difficult visual search task across the circles or discriminated the orientation of a small rectangle at fixation. In the distributed manipulation, the participants either performed a pop-out visual search among the circles or discriminated the orientation of a rectangle surrounding the objects. The participants were more accurate at the averaging task when the manipulation induced a distributed attentional state. In contrast, the participants were better at reporting the size of a single object when the manipulation induced a focused attention state (Chong & Treisman, 2005a). In another experiment, the participants averaged the size of circles that were presented either simultaneously or sequentially. …

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