Dynamic Construction of Reduced Representations in the Brain for Perceptual Decision Behavior.

Summary Over the past decade, extensive studies of the brain regions that support face, object, and scene recognition suggest that these regions have a hierarchically organized architecture that spans the occipital and temporal lobes [ 1–14 ], where visual categorizations unfold over the first 250 ms of processing [ 15–19 ]. This same architecture is flexibly involved in multiple tasks that require task-specific representations—e.g. categorizing the same object as "a car" or "a Porsche." While we partly understand where and when these categorizations happen in the occipito-ventral pathway, the next challenge is to unravel how these categorizations happen. That is, how does high-dimensional input collapse in the occipito-ventral pathway to become low dimensional representations that guide behavior? To address this, we investigated what information the brain processes in a visual perception task and visualized the dynamic representation of this information in brain activity. To do so, we developed stimulus information representation (SIR), an information theoretic framework, to tease apart stimulus information that supports behavior from that which does not. We then tracked the dynamic representations of both in magneto-encephalographic (MEG) activity. Using SIR, we demonstrate that a rapid (∼170 ms) reduction of behaviorally irrelevant information occurs in the occipital cortex and that representations of the information that supports distinct behaviors are constructed in the right fusiform gyrus (rFG). Our results thus highlight how SIR can be used to investigate the component processes of the brain by considering interactions between three variables (stimulus information, brain activity, behavior), rather than just two, as is the current norm. Highlights • We show how the brain reduces high-dimensional input into decision representations • Occipital cortex reduces features irrelevant for behavior ∼170 ms post stimulus • Past 170 ms, fusiform gyrus combines the features supporting behavioral decisions In a decision task, Zhan et al. visualize within a new information theoretic framework the dynamic representation of visual information in brain activity. They demonstrate rapid reduction of behaviorally irrelevant information in the occipital cortex and a combination of the features that supports distinct decisions in the right fusiform gyrus. [ABSTRACT FROM AUTHOR]