Related Experiment Video
Updated: May 2, 2026

Frame-by-Frame Video Analysis of Idiosyncratic Reach-to-Grasp Movements in Humans
Published on: January 15, 2018
Dissociable systems for visually guided navigation versus reaching and grasping in human parietal cortex
Hee Kyung Yoon1, Yaelan Jung1, Daniel D Dilks1
1Department of Psychology, Emory University, 36 Eagle Row, Atlanta, GA, 30322, United States.
Abstract:
Parietal cortex is thought to support visually guided actions, but whether it contains distinct regions specialized for different actions-such as navigation, reaching, and grasping-remains unknown. Prior work implicates the superior parietal lobule (SPL) in navigation and the superior parietal occipital cortex (SPOC) in reaching and grasping, yet whether these are truly dissociable is unclear. We addressed this using fMRI in adults. Participants viewed four stimulus types: Dynamic Scenes (first-person motion through scenes), Static Scenes (static images from these movies), Contextual Reaching and Grasping (first-person reaching and grasping on a scene background), and Isolated Reaching and Grasping (reaching and grasping actions on a black background). A double dissociation emerged: SPL responded significantly more to Dynamic than Static Scenes-consistent with its role in visually-guided navigation-and, critically, more to Dynamic Scenes than either reaching and grasping condition. By contrast, SPOC responded significantly more to both reaching and grasping conditions than to either scene condition. Resting-state functional connectivity further supported this double dissociation: SPL showed stronger connectivity with "leg-motor" than "arm-motor" cortex, whereas SPOC showed the opposite pattern. These findings reveal two distinct parietal systems: SPL for visually-guided navigation and SPOC for visually-guided reaching and grasping-clarifying how the parietal cortex organizes visually guided action.
Related Concept Videos
Somatosensory, Motor, and Association Cortex
Somatosensation
Motor and Sensory Areas of the Cortex
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex....
Major Somatic Sensory Pathways
Association Areas of the Cortex
Prefrontal Association Area: This area is located in the frontal lobe and is involved in planning, decision-making, and moderating social behavior. It connects with primary motor areas,...
Sensory Perception: Organization of the Somatosensory System
The receptor level:
The receptor level is the first stage of sensation. It involves the detection of a stimulus by specialized sensory receptors. The stimulus must arrive within the receptor's receptive field. Next, the receptor converts the energy of the...

