Crowding in the S-cone pathway

Abstract

The spatial extent of interference from nearby object or contours (the critical spacing of “crowding”) has been thoroughly characterized across the visual field, typically using high contrast achromatic stimuli. However, attempts to link this measure with known properties of physiological pathways have been inconclusive. The S-cone pathway, with its ease of psychophysical isolation and known anatomical characteristics, offers a unique tool to gain additional insights into crowding. In this study, we measured the spatial extent of crowding in the S-cone pathway at several retinal locations using a chromatic adaptation paradigm. S-cone crowding was evident and extensive, but its spatial extent changed less markedly as a function of retinal eccentricity than the extent found using traditional achromatic stimuli. However, the spatial extent agreed with that of low contrast achromatic stimuli matched for isolated resolvability. This suggests that common cortical mechanisms mediate the crowding effect in the S-cone and achromatic pathway, but contrast is an important factor. The low contrast of S-cone stimuli makes S-cone vision more acuity-limited than crowding-limited.

Foveal Crowding Resolved

“…Figure 6 extends this analysis more precisely into the fovea, plotting our own data (fitted with model #5) and those from several studies from Table 1 . The dotted line is based on foveal results from contrast thresholds of blurred stimuli, revealing a “size-limited” regime, which also matches results from non-strabismic amblyopia 26 , non-foveal AMD patients 55 and S-cone isolating stimuli 56 . For results on this line, critical spacing is proportional to stimulus size, such that critical spacing = 1.4 × size, a straight line parallel to the identity line on this log-log plot.…”

The generality of the critical spacing for crowded optotypes: From Bouma to the 21st century

“…In an attempt to reconcile the finding of Harrison and Bex (2014) with the other studies cited in Figure 8 , we identified several experimental parameters in their study that were different from the others cited in Figure 8 . First, although their target was also a single letter that could be presented in one of four orientations, unlike the other studies, their flankers were not the same as ( Chung & Mansfield, 2009 ; Coates et al., 2013 ; Coates & Chung, 2016 ; Kooi et al., 1994 ) or highly similar to ( Tripathy & Cavanagh, 2002 ; Tripathy et al., 2014 ) their target. Instead, they used a set of 17 letters presented in their upright positions as flankers.…”

“…The different symbols indicate eccentricity (circles: fovea, stars: 3 degrees, triangles: 5 degrees, squares: 10 degrees) for the contrast experiments ( Coates et al., 2013 ). The four S-cone points ( Coates and Chung, 2016 ) indicate results from 0, 3, 5, and 8 degrees eccentricity, respectively, from lowest to highest on the plot. The dotted and dashed lines show theoretical predictions from Song et al.…”

“… Threshold critical spacing plotted versus threshold unflanked letter size for results from flanked acuity experiments with different contrasts ( Coates et al., 2013 ; Coates & Chung, 2016 ). Colors indicate stimulus conditions (reduced target/flanker contrast or S-cone isolation condition).…”

“…All the data plotted in this figure were obtained when the target and flankers coexisted in time, and thus the target and flanker durations were identical. Two studies ( Coates et al., 2013 ; Coates & Chung, 2016 ) tested several eccentricities. For each of these studies, a one-way ANOVA showed that there was no significant difference in the Bouma fractions at different eccentricities; therefore, these values were averaged to yield one single value for each study (only one duration was used in these studies).…”