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Isabelle Mareschal, Steven C. Dakin, Peter J. Bex; Dynamics of collinear facilitation assessed using classification images. Journal of Vision 2005;5(8):175. doi: 10.1167/5.8.175.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast sensitivity for detecting a Gabor pattern is facilitated by the presence of collinear flanking Gabor elements (Polat and Sagi, Vision Research, 33, 993–999, 1993). We examined the spatial and temporal properties of such facilitation using a psychophysical reverse correlation paradigm. This involved subjects performing a 2AFC task- the detection of a target (2 c/deg Gabor ) embedded in two dimensional noise. A staircase procedure varied target contrast and attempted to converge on a level that maintained detection performance at a constant (75% correct) level. Subjects performed the detection task in the presence and absence of 30% contrast flanking Gabors, spatially arranged to optimize facilitation (Woods et al., Vision Research, 42, 733–745, 2002). The orientation and phase of the flankers relative to the target were varied independently. In order to probe the dynamic properties of facilitation, the noise was either static (duration = 250ms) or dynamic (520 ms). True 14 bit grey scale resolution was obtained using a Bits++ system (Cambridge Research Systems). Classification images (CI) were obtained by conventional means and were then fit with two dimensional Gabor functions to determine the parameters of the perceptive field supporting detection of the target. We report that in both the static and dynamic conditions, the presence of flankers led to facilitation only when they were of the same orientation and phase as the target. The CIs from static noise conditions demonstrate that observers' perceptive fields were well-matched to the target stimulus. The CIs from the dynamic noise condition reveal that subjects rely mainly on the initial frames of the sequence to perform the task, suggesting that the facilitation effects are both rapid and are temporally lowpass tuned.
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