Summary statistics of size: Fixed processing capacity for multiple ensembles but unlimited processing capacity for single ensembles.

Abstract

We assessed the processing capacity of establishing statistical summary representations (SSRs) of mean size in visual displays using the simultaneous-sequential method. Four clusters of stimuli, each composed of several circles with various diameters, were presented around fixation. Observers searched for the cluster with the largest or smallest mean size. In the simultaneous condition, all four clusters were presented concurrently; in the sequential condition, the clusters appeared two at a time. We found that the processing capacity of SSRs for multiple ensembles was as extreme as a fixed-rate bottleneck process (Experiment 1). A control experiment confirmed that this was not caused by having to compare the results of multiple averaging processes (Experiment 2). In contrast to computing SSRs across ensembles, computing SSRs for a single ensemble using the same stimuli was consistent with unlimited-capacity processing (Experiment 3). Contrary to existing claims, summary representations appear to be extracted independently for items within single ensembles but not multiple ensembles. A developing understanding of capacity limitations in perceptual processing is discussed.

What is the Bandwidth of Perceptual Experience?

“…This finding is consistent with earlier studies claiming that an ensemble takes up approximately the same amount of space in working memory as an individual object [91–93]. In addition, observers are more accurate at processing multiple ensembles when they are presented sequentially, rather than simultaneously [94,95], suggesting that ensembles compete for limited cognitive resources. Finally, the precision of ensemble representations varies as a function of the allocation of attention (i.e., focused versus distribute) [96].…”

Effects of ensemble complexity and perceptual similarity on rapid averaging of hue

“…Because the distractor is always more similar to one of the two element colors than the mean color is to either one individually, it may be that the distractor is erroneously chosen due to a bias toward the individual representations of the ensembles hues rather than the ensemble mean. The fact that this effect disappears when there are intermediate hues also present (i.e., in the 20-JND, four-color condition) could be taken to suggest that individual representations no longer bias the choice, perhaps due to the constraints of visual working memory inhibiting the encoding of individual items (e.g., Alvarez & Oliva, 2008;Attarha, Moore, & Vecera, 2014;Baijal et al, 2013;Chong & Treisman, 2005a;Corbett & Oriet, 2011;De Fockert & Marchant, 2008). When the hue range is even greater (i.e., 28 JNDs, two colors), we suggest that the difference between distractor and element hues is sufficiently large that similarity to element colors is not strong enough to bias responses toward either option of the 2AFC, so mean accuracy is near chance.…”

Individual differences in ensemble perception reveal multiple, independent levels of ensemble representation.

“…Evidence for the existence of specialized mechanisms comes from the absence of a set size effect (i.e., ensemble representation precision is fairly constant regardless of the number of items in the set; Attarha, Moore, & Vecera, 2014;Chong & Treisman, 2003Haber man & Whitney, 2009), the speed at which ensembles may be derived (as low as 50 ms), and the availability of ensemble information even when individual item information is unavailable (i.e., as undercrowded conditions or change blindness paradigms; Fischer & Whitney, 2011;Haberman & Whitney, 2011;Parkes et al, 2001). Although there is some suggestion that ensemble rep resentation of size could potentially be explained by sampling just one or two items from an entire array (i.e., not a specialized ensemble mechanism; Myczek & Simons, 2008), there is substan tial evidence showing that many ensemble types are processed in a manner akin to textures (Balas, Nakano, & Rosenholtz, 2009), even when individual item information cannot be resolved (Fischer & Whitney, 2011;Haberman & Whitney, 2011) and therefore cannot be individually sampled.…”