Amirali Soltani Tehrani¹ (), Kristin Woodard², Emalie McMahon², Leah Ettensohn², Natalia Pallis-Hassani², John Ingeholm², Leslie Ungerleider², Chris Baker², Maryam Vaziri-Pashkam^1,2; ¹Movement and Visual Perception lab, Department of Psychological and Brain Sciences, University of Delaware, ²Laboratory of Brain and Cognition, National Institute of Mental Health

The human visual system supports a broad range of behaviors toward objects, from recognizing them to performing actions on them. Object representations have been found in both the human occipitotemporal and parietal cortices, yet we have a limited understanding of how these representations support such diverse behaviors. In this fMRI study, we focused on two behaviors—grasp movements and object similarity judgments—and investigated how the representations in parietal and occipitotemporal cortex relate to each behavior. In behavioral experiments, we used a set of 64 3D-printed objects and measured two behaviors: an online odd-one-out task in which participants selected the most distinct item from sets of three object pictures, and hand-kinematic recordings as participants grasped and held the objects. In the fMRI experiment, participants viewed and grasped the same 3D-printed objects. The objects were placed on a table, and participants viewed them through a mirror for two seconds; eight seconds later they were instructed to grasp and hold the object, allowing us to separate motor-related responses from visual responses. Two regions of interest—the lateral occipital cortex (LOC) and the anterior intraparietal area (AIP)—were examined, and a representational similarity analysis (RSA) was performed to evaluate how their response patterns related to the two behaviors. During the visual phase, LOC responses were more strongly related to the odd-one-out behavior, whereas AIP did not show this similarity pattern. During the grasp phase, AIP patterns related to both the grasp and the odd-one-out behaviors, while LOC did not show this similarity pattern. These findings highlight the distinct roles of object-selective regions across the visual cortex, with LOC encoding semantic qualities independent of action and AIP expressing both semantic and grasp-based features, suggesting that parietal regions simultaneously encode visual and motor representations to support coordinated actions toward objects.