May 2008
Volume 8, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   May 2008
Cross-talk between luminance-defined and contrast-defined detection processing revealed by asymmetric lateral spatial interactions
Author Affiliations
  • M Izzuddin Hairol
    Anglia Vision Research, Anglia Ruskin University
  • Sarah J. Waugh
    Anglia Vision Research, Anglia Ruskin University
Journal of Vision May 2008, Vol.8, 268. doi:10.1167/8.6.268
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      M Izzuddin Hairol, Sarah J. Waugh; Cross-talk between luminance-defined and contrast-defined detection processing revealed by asymmetric lateral spatial interactions. Journal of Vision 2008;8(6):268. doi: 10.1167/8.6.268.

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

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Abstract

Lateral spatial interactions between stimuli defined by different characteristics can reveal independence or otherwise, of processing streams. Foveal detection thresholds for luminance-defined and contrast-defined blobs in the presence of fixed modulation, laterally placed blobs (separations of 0 – 6 deg) were measured in 4 observers with normal vision. Blobs were constructed by adding or multiplying random-dot dynamic noise with a Gaussian (sd = 0.25 deg and 0.5 deg). Detection thresholds measured for luminance-defined blobs placed between highly visible (∼10x threshold) luminance-defined flankers (111) and for contrast-defined blobs placed between highly visible contrast-defined flankers (222) produces a similar pattern of lateral interaction effects. Threshold elevation occurs for overlapping blobs, however when they are completely separated by 1–3 deg (4–12 sd units) there is facilitation where thresholds are about 20–50% lower than when no flankers are present. The region of facilitation is not consistently matched by shallow psychometric function slopes. Detection thresholds measured for luminance-defined blobs placed between highly visible contrast-defined flankers (212) are relatively raised for separations of 0.5 to 2 deg with otherwise minimal or facilitatory effects for all other separations. For detection thresholds measured for contrast-defined blobs placed between highly visible luminance-defined flankers (121), relative facilitation occurs in this region. However psychometric function slopes for both mixed conditions show similar patterns with steeper slopes in the 0.5–2 deg separation region (β∼2.5) compared to those found for thresholds measured without any flankers (β∼1–1.5). These findings favour a model with two parallel processing streams for the detection of luminance-defined and contrast-defined targets, rather than a single stream. They also suggest that there is some cross-talk between these streams. Neural contributions must be considered, as uncertainty reduction due to the presence of visible flanking blobs, cannot consistently explain facilitation effects.

Hairol, M. I. Waugh, S. J. (2008). Cross-talk between luminance-defined and contrast-defined detection processing revealed by asymmetric lateral spatial interactions [Abstract]. Journal of Vision, 8(6):268, 268a, http://journalofvision.org/8/6/268/, doi:10.1167/8.6.268. [CrossRef]
Footnotes
 MIH is supported by a Malaysian Government PhD Scholarship through the University of Kebangsaan Malaysia Support also from the Anglia Ruskin University Research Capacity Fund.
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