December 2006
Volume 6, Issue 13
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OSA Fall Vision Meeting Abstract  |   December 2006
Regions of human visual cortex sensitive to small vernier offsets as determined by EEG source-imaging
Author Affiliations
  • Anthony M. Norcia
    Smith-Kettlewell Eye Research Institute
  • Mark W. Pettet
    Smith-Kettlewell Eye Research Institute
  • Vladimir Y. Vildavski
    Smith-Kettlewell Eye Research Institute
  • Alex R. Wade
    Smith-Kettlewell Eye Research Institute
  • L. Greg Appelbaum
    Duke University, Durham, NC
Journal of Vision December 2006, Vol.6, 21. doi:10.1167/6.13.21
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      Anthony M. Norcia, Mark W. Pettet, Vladimir Y. Vildavski, Alex R. Wade, L. Greg Appelbaum; Regions of human visual cortex sensitive to small vernier offsets as determined by EEG source-imaging. Journal of Vision 2006;6(13):21. doi: 10.1167/6.13.21.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Humans can determine the relative position of visual features with a precision (‘vernier acuity’) better than the sampling resolution of the cone mosaic. Here we use high-density EEG recordings combined with distributed source imaging methods to identify two regions of visual cortex that underlie the detection of near-threshold vernier offsets. Eight observers were presented with a set of 1 arc min vernier offsets that were periodically introduced and withdrawn from a 2 cpd square wave luminance grating at 3.75 Hz (alignment/misalignment). The offset regions of the grating alternated with static regions that served as a position reference. Psychophysical thresholds for this target are in the range of 15–30 arc sec (Norcia et al., 1999). This condition was contrasted with a control condition in which the 1 arc min vernier offsets displaced symmetrically with respect to the reference (misalignment/misalignment). EEG responses to each condition were recorded over 128 channels and were averaged at each electrode across observers. These “sensor-space” averages were aligned to an individual observer's head model generated from a structural MRI. Current density on the cortical surface was determined by a minimum norm inverse. Subtraction of the misalignment/misalignment condition from the alignment/misalignment condition isolates activity that is specific to the relative position of the offsets and the reference. This activity is maximal at the occipital pole (areas V1,V2,V3), but there is a secondary maximum in the middle occipital gyrus, bilaterally. This is the first evidence for a high-resolution position mechanism outside of the classical retinotopic areas.

Norcia, A. M. Pettet, M. W. Vildavski, V. Y. Wade, A. R. Appelbaum, L. G. (2006). Regions of human visual cortex sensitive to small vernier offsets as determined by EEG source-imaging [Abstract]. Journal of Vision, 6(13):21, 21a, http://journalofvision.org/6/13/21/, doi:10.1167/6.13.21. [CrossRef]
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