Variations in crowding, saccadic precision, and spatial localization reveal the shared topology of spatial vision

Abstract

Visual sensitivity varies across the visual field in several characteristic ways. For example, sensitivity declines sharply in peripheral (vs. foveal) vision and is typically worse in the upper (vs. lower) visual field. These variations can affect processes ranging from acuity and crowding (the deleterious effect of clutter on object recognition) to the precision of saccadic eye movements. Here we examine whether these variations can be attributed to a common source within the visual system. We first compared the size of crowding zones with the precision of saccades using an oriented clock target and two adjacent flanker elements. We report that both saccade precision and crowded-target reports vary idiosyncratically across the visual field with a strong correlation across tasks for all participants. Nevertheless, both group-level and trial-by-trial analyses reveal dissociations that exclude a common representation for the two processes. We therefore compared crowding with two measures of spatial localization: Landolt-C gap resolution and three-dot bisection. Here we observe similar idiosyncratic variations with strong interparticipant correlations across tasks despite considerably finer precision. Hierarchical regression analyses further show that variations in spatial precision account for much of the variation in crowding, including the correlation between crowding and saccades. Altogether, we demonstrate that crowding, spatial localization, and saccadic precision show clear dissociations, indicative of independent spatial representations, whilst nonetheless sharing idiosyncratic variations in spatial topology. We propose that these topological idiosyncrasies are established early in the visual system and inherited throughout later stages to affect a range of higher-level representations.O ur sensitivity to visual stimuli varies substantially across the visual field with characteristic patterns that are evident across a wide range of tasks. Most notably, our ability to see fine detail decreases sharply as objects move into peripheral vision (1). These abilities are further disrupted by crowding, the impairment of object recognition in clutter, which also increases with eccentricity (2, 3). Both of these effects have been attributed to an overrepresentation of the fovea at the expense of peripheral vision, known as "cortical magnification" (4, 5), which has been observed in a range of retinotopically organized areas of the brain (6, 7). Here we ask whether other variations in visual sensitivity can similarly be attributed to topological principles within the visual system and consider whether these variations might share a common source.Variations across the visual field are particularly apparent with crowding, a process that presents the fundamental limitation on object recognition in peripheral vision (8). Crowding disrupts the recognition of a target object when flanker objects fall within a surrounding "interference zone." As well as increasing in size with eccentricity, these zones show an elliptical shap...

Idiosyncratic Perception: A Link Between Acuity, Perceived Position, and Apparent Size

“…This also replicates the vertical meridian asymmetry in both human and non-human primates [5,24]. A more recent study carried out by Greenwood and his colleagues [25] found that crowding zones and saccadic error zones are on average larger along the vertical than horizontal meridian and that there are variations between observers, which is consistent with what we showed in the current study. Our study goes beyond previous ones by showing that the individual differences in acuity, perceived position, and perceived size are unique to the individual observer, are highly reliable, and are not due to a group level effect.…”

Visual working memory is independent of the cortical spacing between memoranda

“…Figure 3C shows the critical 406 spacing estimates for all observers and the median for the group. Critical spacing estimates 407 19 span an almost-fourfold range, and such between-subjects variability has been reported 408 previously (Greenwood, Szinte, Sayim, & Cavanagh, 2017;Petrov & Meleshkevich, 2011). 409 To control for between-subjects crowding variability in the memory experiment, and 410 therefore control for cortical spacing variability across participants, we adjusted the spatial 411 range of memoranda in the memory experiment to be either 0.75 times ("crowded") or 1.5 412 times ("uncrowded") an observer's critical spacing.…”

Cortical reorganization of peripheral vision induced by simulated central vision loss

“…A link between the oculomotor control and form processing in peripheral vision has been suggested in previous psychophysical studies. By measuring the size of the crowding zone and the saccade-landing zone, Greenwood et al (2017) demonstrated that the saccadic precision and crowding covary across the visual fields. Harrison et al (2013) showed that eye movement preparation effectively reduces the critical spacing of the crowding zone.…”