Flanker effects in peripheral contrast discrimination—psychophysics and modeling

Abstract

We studied lateral interactions in the periphery by measuring how contrast discrimination of a peripheral Gabor patch is affected by flankers. In the psychophysical experiments, two Gabor targets appeared simultaneously to the left and right of fixation (4 degrees eccentricity). Observers reported which contrast was higher (spatial 2-alternative-forced-choice). In different conditions, Gabor flankers of different orientation, phase, and contrast were present above and below the two targets, at a distance of three times the spatial Gabor period. The data show that collinear flanks impair discrimination performance for low pedestal contrasts but have no effect for high pedestal contrasts. The transition between these two result patterns occurs typically at a pedestal contrast which is similar to the flanker contrast. For orthogonal flanks, we find facilitation at low pedestal contrasts, and suppression at intermediate contrasts. We account for this complex interaction pattern by a model that assumes that flankers can provide additive input to the target unit, and that they further contribute to the target's gain control, but only in a limited range of pedestal contrasts; once the target contrast exceeds a critical value, inhibition becomes subtractive rather than divisive. We further make specific propositions on how this model could be implemented at the neuronal level and show that a simple integrate and fire unit that receives time-modulated inhibition behaves in a fashion strikingly similar to the model inferred from the psychophysical data.

Perceptual learning in contrast detection: presence and cost of shifts in response criteria

“…This is not to say that the possibility of response bias is ignored in existing work. Indeed, in most work, investigators have been exceedingly careful to balance response alternatives in order to minimize the potential effects of response bias (Dosher & Lu, 1999;Lu & Dosher, 2004;Zenger-Landolt & Koch, 2001). Unfortunately, with respect to questions of detection, those alternatives typically have not included the complete absence of the critical stimulus property (i.e., the target property has always been present on each trial).…”

Individual differences in the dynamics of collinear facilitation?

“…Since Polat & Sagi (1993) first demonstrated both facilitation and suppression with such an arrangement, a multitude of spatial (Polat & Sagi 1994;Polat 2009;Polat et al 1998;Zenger-Landolt & Koch 2001;Mizobe et al 2001;Freeman et al 2001;Woods et al 2002;Freeman et al 2004;Giorgi et al 2004;Polat et al 2005;Polat & Sagi 2007;Shani & Sagi 2005;Huang et al 2006;Huang & Hess 2007;Huang et al 2012;Huang & Hess 2008;Sterkin et al 2008;Katkov & Sagi 2010;Wu & Chen 2010;Kéita et al 2011;Lev & Polat 2011;Jachim et al 2015) and temporal (Tanaka & Sagi 1998;Polat & Sagi 2006;Cass & Alais 2006;Huang & Hess 2008;Sterkin et al 2009;Li et al 2010;Sterkin et al 2012) combinations of target and flanker designs have been developed.…”

Two Distinct Mechanisms of Suppression in Human Vision

“…Thus, most of the early psychophysical studies used large grating targets with coextensive masks and therefore tended to confound the effects of overlay and surround suppression. Most recent contrast threshold measurements in the fovea have found that adjacent targets enhance contrast sensitivity (Polat and Sagi, 1993;Yu et al, 2003), whereas studies in the periphery have noted that adjacent targets suppress sensitivity (Chubb et al, 1989;Solomon et al, 1993;Wilkinson et al, 1997;Snowden and Hammett, 1998;Xing and Heeger, 2001;Zenger-Landolt and Koch, 2001). We asked whether there are two distinct suppressive mechanisms in human vision and whether they are consistent with the neurophysiological suppression mechanisms.…”