Comparing explicit and implicit ensemble perception: 3 stimulus variables and 3 presentation modes.

Visual scenes are too complex for one to immediately perceive all their details. As suggested by Gestalt psychologists, grouping similar scene elements and perceiving their summary statistics provides one shortcut for evaluating scene gist. Perceiving ensemble statistics overcomes processing, attention, and memory limits, facilitating higher-order scene understanding.

Perceptual learning of ensemble and outlier perception.

Previous studies have demonstrated a complex relationship between ensemble perception and outlier detection. We presented two array of heterogeneously oriented stimulus bars and different mean orientations and/or a bar with an outlier orientation, asking participants to discriminate the mean orientations or detect the outlier. Perceptual learning was found in every case, with improved performance accuracy and speeded responses.

Comparing set summary statistics and outlier pop out in vision.

Visual scenes are too complex to perceive immediately in all their details. Two strategies (among others) have been suggested as providing shortcuts for evaluating scene gist before its details: (a) Scene summary statistics provide average values that often suffice for judging sets of objects and acting in their environment. Set summary perception spans simple/complex dimensions (circle size, face emotion), various statistics (mean, variance, range), and separate statistics for discernible sets.

Global statistics are not neglected.

In the framework of Reverse Hierarchy Theory it was suggested that initial vision at a glance brings the gist of the scene to conscious perception using explicit high cortical level representations, which are initially built by implicit bottom-up processing (Hochstein & Ahissar, 2002). Only later return to lower cortical level representations introduces local details to conscious perception. Global statistics of similar elements are perceived rapidly and accurately, suggesting they are included in the initial perception of the gist of the scene, not depending on prior conscious perception of local details.

Computing an average when part of the population is not perceived.

The syndrome of unilateral spatial neglect (USN) after right-hemisphere damage is characterized by failure of salient left-sided stimuli to activate an orienting response, attract attention, and gain access to conscious awareness. The explicit failure processing left-sided visual information is not uniform, however, and patients seem to be more successful performing certain visual tasks than others. The source of this difference is still not clear.