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Published August 2009 | Supplemental Material
Journal Article Open

Parietal Reach Region Encodes Reach Depth Using Retinal Disparity and Vergence Angle Signals

Abstract

Performing a visually guided reach requires the ability to perceive the egocentric distance of a target in three-dimensional space. Previous studies have shown that the parietal reach region (PRR) encodes the two-dimensional location of frontoparallel targets in an eye-centered reference frame. To investigate how a reach target is represented in three dimensions, we recorded the spiking activity of PRR neurons from two rhesus macaques trained to fixate and perform memory reaches to targets at different depths. Reach and fixation targets were configured to explore whether neural activity directly reflects egocentric distance as the amplitude of the required motor command, which is the absolute depth of the target, or rather the relative depth of the target with reference to fixation depth. We show that planning activity in PRR represents the depth of the reach target as a function of disparity and fixation depth, the spatial parameters important for encoding the depth of a reach goal in an eye centered reference frame. The strength of modulation by disparity is maintained across fixation depth. Fixation depth gain modulates disparity tuning while preserving the location of peak tuning features in PRR neurons. The results show that individual PRR neurons code depth with respect to the fixation point, that is, in eye centered coordinates. However, because the activity is gain modulated by vergence angle, the absolute depth can be decoded from the population activity.

Additional Information

© 2009 by the The American Physiological Society. Submitted 12 March 2008; accepted in final form 10 May 2009. First published May 13, 2009; doi:10.1152/jn.90359.2008 This work was funded by National Institutes of Health and Office of Naval Research. We thank G. Mulliken, E. Hwang, and H. Cui, for helpful comments on the manuscript; Z. Nadasdy for useful discussions; K. Pejsa, N. Sammons, L. Martel, J. Baer, and C. Lindsell for help with animal handling and veterinary assistance; V. Shcherbatyuk for computer support; T. Yao for administrative assistance; and R. Panagua and M. Walsh for laboratory equipment construction. We also thank the reviewers for comments and suggestions.

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Additional details

Created:
August 20, 2023
Modified:
October 19, 2023