Vision Sciences Society Annual Meeting Abstract
The capacity of fine vision of individual object is limited by the "bottleneck" of attention and working memory. Still, at every moment we see large collections of objects. What exactly happens to individual representations when the observer attempts to distribute attention between multiple objects? One view is that a fixed number of objects are represented with good fidelity while others are represented with poor fidelity. Another theory is that attention is evenly distributed among all objects but fidelity decreases as set size grows. This debate is one in the core of a theory of summary representation of multiple objects (Alvarez, 2011; Myczek & Simons, 2008). Here we directly tested how the capacity and fidelity change with set size. Participants were briefly shown sets of 1, 2, 4, or 8 circles of various sizes. Then, one of the circles increased or decreased in size by 2- 20% (change step 2%). The change was synchronized with a global background flash masking the local transient caused by the circle change. Observers had to respond whether they had seen an increment or decrement in any of the circles (2AFC). These manipulations rely on an assumption that one needs attention to the stimulus to spot a change (Rensink et al., 1997). Psychometric functions were fit using normal cumulative density functions. We found that the set size affects the probability of correct response at which the function reaches a plateau: the larger was a set size, the lower was such probability. The standard deviations of the functions typically associated with fidelity were relatively similar across set sizes within each observer. We conclude, therefore, that, when observers perceive multiple objects during a short time, they focus attention on a limited sample of items represented with the same fidelity, rather than evenly distribute it among all the objects.