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Barbara Zenger-Landolt, Christof Koch; Attention reduces flanker suppression. Journal of Vision 2001;1(3):342. doi: 10.1167/1.3.342.
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© ARVO (1962-2015); The Authors (2016-present)
We used a pre-cued visual search task to study attentional effects on contrast discrimination of peripheral Gabor patches in the presence of flanks. In the unflanked condition, eight Gabor patches were presented on an imaginary circle (radius 3.5 deg) centered on a fixation mark, with the orientation of each patch being orthogonal to the imaginary circle (like short sun-rays). In the flanked condition, these eight patches were flanked inside and outside by collinear Gabor patches of 35% contrast (extending every “sun ray”). In each trial, one of the 8 central patches had a higher contrast than the other 7 patches, and the observers task was to indicate the location of this patch (spatial 8AFC). Contrast discrimination thresholds were measured for an exhaustive range of pedestal contrasts. There were two attentional conditions: in the unattended condition, all 8 possible target locations were precued and attention was thus presumably distributed. In the attended condition, precues indicated two locations, on opposite sides of the circle, one of which contained the target; in this case, attention could be focussed on the two possible target locations. We reproduced previous findings (Zenger & Koch, ARVO 2000) that flanker effects on contrast discrimination in the periphery depend on the relative contrast of target and flanks: if the target contrast is below the flank contrast, discrimination is impaired, while targets above flanker contrast remain unaffected. Our present data indicate that whenever the presence of flanks impairs performance (low pedestal contrasts) attention reduces this impairment and improves performance; by contrast, attention does not affect performance when no flanker effects are observed (high pedestal contrasts). These results suggest that attention affects contrast discrimination thresholds by reducing the inhibition from the flanks to the target.
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