Cortical distance unifies the extent of parafoveal contour interactions

Abstract

It is well known that crowding, the disruptive influence of flanking items on identification of targets, is the primary limiting factor to object identification in the periphery, while limits in the fovea are more determined by the ability to resolve individual items. Whether this is a dichotomous or merely a quantitative difference, and the transition between these two regimes, has remained unexplained. Here, using an adaptive optics system for optimal control of optical and stimulus factors, we measured threshold acuity for identification of Tumbling Es flanked by bars at a variety of flanker spacings and eight eccentricities in the parafovea. Thresholds at each eccentricity were influenced by resolution, contour interaction, and a saturating pedestal effect. When target-flanker spacing was plotted in terms of cortical distance, a single canonical clipped-line fit unified the resultant curves. The critical spacing for letters flanked by bars was found to be 1.3 to 1.5 cortical millimeters, corresponding to approximately 0.1*E outside the fovea.

Foveal crowding appears to be robust to normal aging and glaucoma unlike parafoveal and peripheral crowding

“…Visual crowding is a perceptual phenomenon that impairs the recognition of targets when surrounded by flankers ( Balas, Nakano, & Rosenholtz, 2009 ; Bouma, 1970 ; Greenwood, Szinte, Sayim, & Cavanagh, 2017 ; Harrison & Bex, 2015 ; He, Cavanagh, & Intriligator, 1996 ; Kwon & Liu, 2019 ; Parkes, Lund, Angelucci, Solomon, & Morgan, 2001 ; Pelli, & Tillman, 2008 ; Pelli et al, 2004 ; Toet & Levi, 1992 ; Wallis & Bex, 2011 ; Whitney & Levi, 2011 ). Although crowding is typically associated with the peripheral vision, emerging evidence has pointed to the presence of measurable crowding in the foveal vision ( Coates et al, 2018 ; Coates et al, 2022 ; Danilova & Bondarko, 2007 ; Flom et al, 1963 ; Lev et al, 2014 ; Pelli et al, 2016 ; Siderov et al, 2013 ; Strasburger et al, 1991 ; Toet & Levi, 1992 ). Studies have used a variety of tasks, targets (different types and sizes), and flankers (different numbers and types of flankers), under limited or unlimited stimulus durations to measure the spatial extent of foveal crowding and reported a range of approximately 0.0125 degrees to 0.1 degrees for the extent of foveal crowding for normal healthy vision ( Coates et al, 2018 ; Danilova & Bondarko, 2007 ; Flom et al, 1963 ; Marten-Ellis & Bedell, 2021 ; Pelli et al, 2016 ; Siderov et al, 2013 ; Toet & Levi, 1992 ; Wolford & Chambers, 1984 ) as summarized in Figure 2 A(i).…”

“…the minimum spacing between a target and flankers required for reliable target identification), increases with increasing retinal eccentricity ( Bouma, 1970 ; Pelli et al, 2004 ; Whitney & Levi, 2011 ). Thus, visual crowding is known to be more pronounced in the peripheral vision, whereas little crowding exists in the foveal vision ( Coates, Jiang, Levi, & Sabesan, 2022 ; Coates, Levi, Touch, & Sabesan, 2018 ; Danilova & Bondarko, 2007 ; Flom, Weymouth, & Kahneman, 1963 ; Lev, Yehezkel, & Polat, 2014 ; Levi, Klein, & Hariharan, 2002 ; Pelli, Waugh, Martelli, Crutch, Primativo, Yong, Rhodes, Yee, Wu, Famira, & Yiltiz, 2016 ; Siderov, Waugh, & Bedell, 2013 ; Strasburger, Harvey, & Rentschler, 1991 ; Toet & Levi, 1992 ). However, some conditions, such as amblyopia, exhibit significantly increased foveal crowding ( Bonneh, Sagi, & Polat, 2007 ; Flom et al, 1963 ; Hariharan, Levi, & Klein, 2005 ) compared to what is expected from normal vision.…”

A common cortical basis for variations in visual crowding

“…Given the prominence of cortical distance as an explanation of variations in crowding (Levi, Klein, & Aitsebaomo, 1985; Motter & Simoni, 2007; Pelli, 2008; Coates et al, 2022), we first sought to dissociate physical from cortical distance using the division of the left and right sides of the visual field, which project to the right and left hemispheres, respectively (Sereno et al, 1995; Wandell, Dumoulin, & Brewer, 2007). Liu et al (2009) noted that this hemispheric separation of the hemifields would cause a contralateral flanker on the opposite side of the vertical meridian to the target to be more distant cortically than an ipsilateral flanker on the same side of the meridian, despite both having matched physical distance.…”

“…Because retinotopic visual areas show cortical magnification, with an expanded representation of the visual field around the fovea relative to the periphery (Daniel & Whitteridge, 1961; Wandell, Dumoulin, & Brewer, 2007; Strasburger, 2020), target and flanker elements with a fixed distance in the visual field would shift closer together cortically as they moved into the periphery. The increase in crowded performance decrements with eccentricity has been attributed to this decrease in cortical distance (Levi, Klein, & Aitsebaomo, 1985; Motter & Simoni, 2007; Pelli, 2008; Coates, Jiang, Levi, & Sabesan, 2022). Variations in the effect of crowding on appearance have also been linked with cortical distance, with the predominance of repulsion at parafoveal eccentricities attributed to the larger cortical distance between elements compared to the periphery, where the decrease in cortical distance promotes assimilation (Mareschal, Morgan, & Solomon, 2010).…”

Crowding: Recent advances and perspectives

“…Although many studies using vernier targets showed similar effects in the fovea and in the periphery (e.g., Sayim, Westheimer, & Herzog, 2010 ; Manassi, Sayim, & Herzog, 2012 ), results for letter targets are less clear. Coates, Jiang, Levi, and Sabesan (2022) investigated crowding with tumbling Es flanked by bars at several eccentricities in the parafovea. Using adaptive optics, they found that the different results at different eccentricities could be well-summarized by a single function, unifying the varying results.…”