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Dave Ellemberg, Bruno Richard, Aaron Johnson, Bruce Hansen; Centre-surround interactions on apparent contrast endure with broad-band stimuli. Journal of Vision 2012;12(9):96. doi: 10.1167/12.9.96.
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When a narrow-band target is presented at the fovea and is flanked by a stimulus with the same spatial characteristics, its apparent contrast is reduced by ~40%. This effect is tuned to orientation and spatial frequency (about one octave). Our objective was to verify whether increasing stimulus complexity (by using broad-band gratings) affects this well-known contrast induction phenomenon (i.e., do suppressive interactions persist when multiple spatial and orientation channels are solicited). The stimuli consisted of cosine luminance gratings that contained multiple spatial frequencies or orientations. The central target had a diameter of 1 deg and the surround a diameter of 6 deg. Contrast was set at 40% for all patterns and all conditions. We used a contrast-matching paradigm that consisted of a two-alternative TFC procedure and the method of constant stimuli. We found that the apparent contrast of a single grating target remains equally reduced (~40% reduction) when the compound surround includes gratings that have a spatial frequency within 0.5 octave and an orientation within 15 deg of the target in addition to a grating with the same characteristics as the target. However, suppression in the apparent contrast of the target is reduced by half (~23 %) when the compound surround includes gratings that have a spatial frequency beyond 1.0 octave and an orientation beyond 30 deg of the target in addition to a grating with the same characteristics as the target. Finally, when the same compound grating is presented in the centre and surround, regardless of the spatial frequencies and orientations included, maximum suppression occurs (~38%). Therefore, suppressive interactions are not a narrow-band or single channel phenomenon, but also occur under a visual context that includes multiple spatial frequencies and orientations.
Meeting abstract presented at VSS 2012
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