Vernier Acuity with Non-simultaneous Targets: The Cortical Magnification Factor Estimated by Psychophysics

Vernier Acuity with Non-simultaneous Targets: The Cortical Magnification Factor Estimated by... The eccentricity at which peripheral thresholds double their foveal value ( E 2 ) may relate to the visual system's anatomical organization. Using a variety of experimental approaches, previous estimates of E 2 for vernier acuity have ranged from less than 0.1 deg to greater than 15.0 deg. This broad range of values seems to challenge the usefulness of E 2 for determining visual topography. We explain that the varying contributions from at least two different regimes, spatial filter and local sign, may explain the broad range of E 2 values found previously. We attempt to limit responses to the local sign regime, where it may be possible to determine the psychophysical analog to the gradient of the cortical spatial grain. In our experiments we measure how vernier task performance falls off with eccentricity. We hypothesize that if the vernier features are adequately separated in time, they will fall outside of the spatial filter's temporal integration span and the local sign regime would then predominate for precise positional processing. Using an interstimulus interval ranging from 20 to 200 msec between the two vernier features, we estimate that vernier thresholds in the local sign regime double at about 0.8 ± 0.2 deg eccentricity, which is similar to anatomical estimates of the eccentricity at which the linear spacing of human cortical units doubles. Copyright © 1996 Elsevier Science Ltd http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Vision Research Elsevier

Vernier Acuity with Non-simultaneous Targets: The Cortical Magnification Factor Estimated by Psychophysics

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Publisher
Elsevier
Copyright
Copyright © 1996 Elsevier Science Ltd
ISSN
0042-6989
eISSN
1878-5646
DOI
10.1016/S0042-6989(96)00109-5
Publisher site
See Article on Publisher Site

Abstract

The eccentricity at which peripheral thresholds double their foveal value ( E 2 ) may relate to the visual system's anatomical organization. Using a variety of experimental approaches, previous estimates of E 2 for vernier acuity have ranged from less than 0.1 deg to greater than 15.0 deg. This broad range of values seems to challenge the usefulness of E 2 for determining visual topography. We explain that the varying contributions from at least two different regimes, spatial filter and local sign, may explain the broad range of E 2 values found previously. We attempt to limit responses to the local sign regime, where it may be possible to determine the psychophysical analog to the gradient of the cortical spatial grain. In our experiments we measure how vernier task performance falls off with eccentricity. We hypothesize that if the vernier features are adequately separated in time, they will fall outside of the spatial filter's temporal integration span and the local sign regime would then predominate for precise positional processing. Using an interstimulus interval ranging from 20 to 200 msec between the two vernier features, we estimate that vernier thresholds in the local sign regime double at about 0.8 ± 0.2 deg eccentricity, which is similar to anatomical estimates of the eccentricity at which the linear spacing of human cortical units doubles. Copyright © 1996 Elsevier Science Ltd

Journal

Vision ResearchElsevier

Published: Feb 1, 1997

References

  • Perceptual learning in parafoveal vision
    Beard, B.L.; Levi, D.M.; Reich, L.
  • Two systems in detection of visual motion
    Bonnet, C.
  • Magnification factor and receptive field size in foveal striate cortex of the monkey
    Dow, B.M.; Snyder, A.Z.; Vautin, R.G.; Bauer, R.
  • Learning by assertion: two methods for calibrating a linear visual system
    Maloney, L.T.; Ahumada, A.J.
  • Vernier acuity predicted from changes in the light distribution of the retinal image
    Morgan, M.J.; Aiba, T.S.
  • An estimation and application of the human cortical magnification factor
    Rovamo, J.; Virsu, V.
  • How vernier acuity depends on contrast
    Wehrhahn, C.; Westheimer, G.

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