George Alvarez

Computational Visual Cognition Lab, Brain & Cognitive Science, MIT

Although we can only attend to a few objects at once, our perceptual experience is rich and detailed. What type of representation could enable this subjective experience? I have explored the possibility that perception consists of two types of representations: (1) a detailed representation of the currently attended objects, plus (2) a statistical summary of information outside the focus of attention. This point of view makes a distinction between individual features and statistical summary features. For example, a single object's location is an individual feature. In contrast, the center of mass of several objects (the centroid) is a statistical summary feature, because it collapses across individual details and represents the group overall. I will present evidence that the visual system can compute statistical summary features outside the focus of attention even when local features cannot be reported. This finding holds for simple summary statistics including the centroid of a set of uniform objects, and for texture patterns that resemble natural image statistics.Thus, it appears that information outside the focus of attention can be represented at an abstract level which lacks local detail, but nevertheless carries a precise statistical summary of the scene. The term 'ensemble features' refers to a broad class of statistical summary features, which we propose collectively comprise the representation of information outside the focus of attention.