June 2006
Volume 6, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   June 2006
Snakes are as fast as ladders: Evidence against the hypothesis that contrast facilitation mediates contour detection
Author Affiliations
  • Keith A. May
    McGill University, Montreal, Canada
  • Robert F. Hess
    McGill University, Montreal, Canada
Journal of Vision June 2006, Vol.6, 337. doi:10.1167/6.6.337
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      Keith A. May, Robert F. Hess; Snakes are as fast as ladders: Evidence against the hypothesis that contrast facilitation mediates contour detection. Journal of Vision 2006;6(6):337. doi: 10.1167/6.6.337.

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

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Abstract

It is easy to detect a “snake” consisting of spatially separated, collinear elements, embedded in a field of randomly oriented elements (Field, Hayes & Hess, 1993, Vision Research, 33, 173–193). Performance is poor when elements are oriented 45 degrees to the contour, but improves when elements are orthogonal to the contour (“ladders”) (Ledgeway, Hess & Geisler, 2005, Vision Research, 45, 2511–2522). Contour detection has been related to the phenomenon of contrast facilitation, whereby the contrast threshold for detection of an element is reduced when it is flanked by other elements: many models assume that contours are detected through the modulation of neuronal activity by the facilitatory signals that underlie contrast facilitation. If this were the case, one would expect contour detection to show similar temporal properties to contrast facilitation. Cass & Spehar (2005, Vision Research, 45, 3060–3073) used a psychophysical procedure to estimate the speed of propagation of contrast facilitation signals; their results suggest that the facilitatory signals from collinear flankers propagate much more slowly than those from non-collinear flankers. We investigated the effect of temporally modulating the orientation of contour elements from collinear to diagonal, or from orthogonal to diagonal. If contour detection and contrast facilitation are mediated by the same mechanisms, then the integration of snake contours should be much slower, and should be disrupted at much lower temporal frequencies, than the integration of ladder contours. We found identical temporal properties for both contour types, suggesting that contour integration is mediated by different mechanisms from contrast facilitation.

May, K. A. Hess, R. F. (2006). Snakes are as fast as ladders: Evidence against the hypothesis that contrast facilitation mediates contour detection [Abstract]. Journal of Vision, 6(6):337, 337a, http://journalofvision.org/6/6/337/, doi:10.1167/6.6.337. [CrossRef]
Footnotes
 This work was supported by CIHR grant MT 108-18
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