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Maryam Vaziri-Pashkam, Kristin Woodard, Leslie Ungerleider; Representations for grasp-relevant parts of objects in the human intraparietal sulcus. Journal of Vision 2020;20(11):1512. https://doi.org/10.1167/jov.20.11.1512.
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Visual object representations have been found in both human occipitotemporal and parietal cortices. Here, we examined how these representations are influenced by the grasp plan. Participants viewed and grasped 3D-printed objects inside an MRI scanner. The objects were put on a table positioned over the body and the participants were able to view the object through a mirror. Objects were one of four mug-shaped items composed of a handle and a body and participants were instructed to grasp the handle. The handle (the grasp-relevant part of the object) was either straight or curved and the body was either round or rectangular. The experiment was a slow event-related design. Objects were put on the table behind an occluder; the occluder was lowered for 2 seconds so that participants would see the objects. The occluder was then raised back to cover the object and 8 seconds later the participants heard a beep instructing them to start the grasp without visual access to the object. This was done to separate the motor-related responses from the visual- and grasp plan-related responses. We focused on two shape-selective regions of interest: one in lateral occipital cortex (LOC) and one in the inferior intraparietal sulcus (inferior IPS). A pattern classification analysis was performed on the visual responses to discriminate either the two objects with the same body and different handles (handle classification), or the two objects with the same handle and different bodies (bodle classification). LOC showed similar classification accuracies for the body and handle, but inferior IPS showed significantly higher pattern classification for handles than bodies. These results demonstrate that grasp plans modulate the object response in the human intraparietal sulcus.
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