RT Journal Article SR Electronic T1 The integration of visual and target signals in V4 and IT during visual object search JF bioRxiv FD Cold Spring Harbor Laboratory SP 370049 DO 10.1101/370049 A1 Noam Roth A1 Nicole C. Rust YR 2018 UL http://biorxiv.org/content/early/2018/07/16/370049.abstract AB Many everyday tasks require us to flexibly map incoming sensory information onto behavioral responses based on context. One example is the act of searching for a specific object, which requires our brain to compare the items in view with a remembered representation of a sought target to determine whether a target match is present. During object search, this comparison is thought to be implemented, in part, via the combination of top-down modulations reflecting target identity with feed-forward visual representations. However, it remains unclear whether these top-down signals are integrated at a single locus within the ventral visual pathway (e.g. V4) or at multiple stages (e.g. both V4 and inferotemporal cortex, IT). To investigate, we compared neural responses in V4 and IT recorded as rhesus monkeys performed a task that required them to identify when a target object appeared across variation in position, size and background context. We found non-visual, task-specific signals in both V4 and IT. To evaluate the plausibility that V4 was the only locus for the integration of top-down signals, we evaluated a number of feed-forward accounts of processing from V4 to IT, including a model in which IT preferentially sampled from the best V4 units, as well as a model that allowed for nonlinear IT computation. IT task-specific modulation could not be accounted for by any of these feed-forward descriptions, suggesting that during object search, top-down signals are integrated directly within IT itself.SIGNIFICANCE To find specific visual objects, the brain must combine top-down information reflecting the identity of a sought target with visual information about objects in view. While top-down signals are known to exist at multiple stages along the ventral visual pathway, the route with which they arrive in each brain area is unclear. Here we present evidence that task-relevant signals in one high-level visual brain area, IT, cannot be described as simply being inherited from an earlier stage of processing, V4, and thus must be integrated directly within IT itself. This study is the first to systematically compare the responses of V4 and IT during an object search task in which objects can appear in different real-world configurations, and it provides important constraints on the neural computations responsible for finding visual targets.