October 2003
Volume 3, Issue 9
Free
Vision Sciences Society Annual Meeting Abstract  |   October 2003
Spatial lateral interactions operate over shorter distances for second-order compared to first-order mechanisms
Author Affiliations
  • Dave Ellemberg McGill
    Vision Research Unit, McGill University, Canada
Journal of Vision October 2003, Vol.3, 613. doi:10.1167/3.9.613
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      Dave Ellemberg McGill, Harriet A Allen, Robert F Hess; Spatial lateral interactions operate over shorter distances for second-order compared to first-order mechanisms. Journal of Vision 2003;3(9):613. doi: 10.1167/3.9.613.

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Abstract

We compared the spatial extent of lateral masking for first- versus second-order images and investigated spatial interactions between these two types of images. To do so we measured the apparent contrast of a target Gabor at fixation, in the presence versus the absence of horizontally flanking Gabors. The Gabors' grating was vertical, had a peak spatial frequency of 3 cpd, and was either added to (first-order) or multiplied with (second-order) binary 2-D noise. Apparent “contrast” (i.e., the perceived difference between the high and low luminance regions of the first-order stimulus, or between the high and low contrast regions of the second-order stimulus) was measured with a contrast-matching paradigm. Using a temporal 2 AFC and the method of constant stimuli, subjects indicated in which interval the central Gabor had the higher “contrast”. For each subject, the first- and second-order Gabors were equated for apparent contrast without the flankers. Two of the authors and two naive observers participated in this study.

When first-order flankers abutted a first-order target the apparent contrast of the target was reduced by 29%, and remained reduced up to an element separation of 6 wavelengths. When second-order flankers abutted a second-order target the apparent contrast of the target was reduced by 23%, and remained reduced up to an element separation of 3 wavelengths. The spatial frequency and orientation tuning of the suppression effect was broader for second- than first-order stimuli. Second-order flankers did not reduce the apparent contrast of the first-order target; however, in three subjects, first-order flankers reduced the apparent contrast of the second-order target. This effect was tuned for spatial frequency.

Therefore, we find that lateral interactions operate over shorter distances for second- than for first-order information, and that these two types of information interact in an asymmetrical fashion.

Ellemberg, D., Allen, H. A., Hess, R. F.(2003). Spatial lateral interactions operate over shorter distances for second-order compared to first-order mechanisms [Abstract]. Journal of Vision, 3( 9): 613, 613a, http://journalofvision.org/3/9/613/, doi:10.1167/3.9.613.
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