August 2009
Volume 9, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   August 2009
Temporal variation of spatial tuning of single units in macaque inferior parietal cortex under normal and distorted visual conditions
Author Affiliations
  • Anushree Karnik
    Center for Molecular and Behavioral Neuroscience, Rutgers University
  • Barbara Heider
    Center for Molecular and Behavioral Neuroscience, Rutgers University
  • Ralph M. Siegel
    Center for Molecular and Behavioral Neuroscience, Rutgers University
Journal of Vision August 2009, Vol.9, 1161. doi:10.1167/9.8.1161
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      Anushree Karnik, Barbara Heider, Ralph M. Siegel; Temporal variation of spatial tuning of single units in macaque inferior parietal cortex under normal and distorted visual conditions. Journal of Vision 2009;9(8):1161. doi: 10.1167/9.8.1161.

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Abstract

Inferior parietal neurons in areas 7a and dorsal prelunate (DP) are spatially tuned for angle of gaze, visual stimuli, and reaching (MacKay 1992; Heider et al., 2006; Heider et al., submitted). The current study explores the evolution of the spatial tuning of single units under normal and distorted vision. Neural activity was recorded in areas 7a and DP contralateral to the reaching arm. The monkey was required to fixate one of nine positions on a touch screen while a visual stimulus (expansion optic flow, radius 6°) appeared behind the fixaiton point. The animal reached ballistically when the flow went from structured to unstructured. A binocular Fresnel prism introduced a 10° visual shift. The trained monkey correctly reached to the physical location of the stimulus within a few trials demonstrating swift adaptation. Each unit was tested under the pre-prism and the prism condition. Activity was assessed during: (1) fixation onset (“eye position signal”), (2) the “visual signal”, (3) during motor preparation and (4) during the ballistic reach. Linear regressions with categorial variables for the four epochs quatified the evolution in spatial tuning. The spatial tuning changed for 78% of the 128 units. An index of variability was computed. The variability in spatial tuning was greater for the prism condition than the pre-prism condition. When the monkey is correcting for the prism, neural circuits may be brought into play within parietal cortex to actively correct for distortion. Such circuits may have more impact on the visuo-spatial tranformation as the actual reaching event becomes temporally proximate. When the prism is absent, no corrections are needed as the perceptual and reach coordinates are in register in eye-centered coordinates. Hence minimal change in spatial tuning occurs as the task progresses.

Karnik, A. Heider, B. Siegel, R. M. (2009). Temporal variation of spatial tuning of single units in macaque inferior parietal cortex under normal and distorted visual conditions [Abstract]. Journal of Vision, 9(8):1161, 1161a, http://journalofvision.org/9/8/1161/, doi:10.1167/9.8.1161. [CrossRef]
Footnotes
 NIH EY09223
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