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Preeti Verghese, Yury Petrov, Suzanne P. McKee; Collinear facilitation is largely due to uncertainty reduction. Journal of Vision 2005;5(8):721. doi: 10.1167/5.8.721.
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© ARVO (1962-2015); The Authors (2016-present)
Starting with Polat & Sagi (1993), several studies have shown that the presence of collinear flankers improves the detection of a central Gabor patch. This result has been interpreted as evidence for collinear facilitation. However, it is important to note that facilitation has been observed only for targets near detection threshold (Chen & Tyler, 2002), where observes act as if uncertain about the properties of the stimulus (Pelli, 1985). So the effect of the flankers may be to reduce the uncertainty about the target location and orientation. If this is true, then other cues to target location and orientation should give rise to a similar decrease in thresholds. To test this hypothesis, we measured contrast detection thresholds for a Gabor target under 3 conditions: (i) target alone, (ii) target surrounded by a low-contrast circle that served as a location cue and (iii) target flanked by two collinear Gabor patches. We also used an adaptive procedure to measure the slope of the psychometric function to determine whether the slopes were considerably lower in the presence of cues that reduced uncertainty, as predicted by signal detection theory. Our results show that the presence of collinear flankers improves detection thresholds by a factor of two. For three of our five observers, the circle alone improves thresholds as much as the collinear flankers. For the other two observers, the circle causes an intermediate improvement, suggesting that these observers also benefit from the orientation information provided by the collinear Gabors. More importantly, the slopes of the psychometric function are much shallower in the presence of the circle or the collinear flankers, indicating that the improved thresholds in these conditions are largely due to significant reductions in uncertainty.
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