Geometrically restricted image descriptors: A method to capture the appearance of shape

Abstract

Shape perception varies depending on many factors. For example, presenting a stimulus in the periphery often yields a different appearance compared with its foveal presentation. However, how exactly shape appearance is altered under different conditions remains elusive. One reason for this is that studies typically measure identification performance, leaving details about target appearance unknown. The lack of appearance-based methods and general challenges to quantify appearance complicate the investigation of shape appearance. Here, we introduce Geometrically Restricted Image Descriptors (GRIDs), a method to investigate the appearance of shapes. Stimuli in the GRID paradigm are shapes consisting of distinct line elements placed on a grid by connecting grid nodes. Each line is treated as a discrete target. Observers are asked to capture target appearance by placing lines on a freely viewed response grid. We used GRIDs to investigate the appearance of letters and letter-like shapes. Targets were presented at 10°eccentricity in the right visual field. Gaze-contingent stimulus presentation was used to prevent eye movements to the target. The data were analyzed by quantifying the differences between targets and response in regard to overall accuracy, element discriminability, and several distinct error types. Our results show how shape appearance can be captured by GRIDs, and how a fine-grained analysis of stimulus parts provides quantifications of appearance typically not available in standard measures of performance. We propose that GRIDs are an effective tool to investigate the appearance of shapes.

Atypical visual field asymmetries in redundancy masking

“…For example, using a gaze-contingent peripheral presentation and appearance capture (drawing) paradigm, frequent omissions and truncations of elements in letter and letter-like targets indicated target diminishment in crowding ( Sayim & Wagemans, 2017 ). Similar results, possibly due to “self-crowding” ( Martelli, Majaj, & Pelli, 2005 ; Zhang, Zhang, Liu, & Yu, 2009 ), were found with complex, peripherally presented letters and letter-like shapes in isolation ( Melnik, Coates, & Sayim, 2021 ). The investigation of errors in peripherally presented lower-case letter trigrams revealed a similar pattern of diminishment in crowding, as letter features appearing in both a flanking letter and the target letter (such as an ascender or descender) were often omitted in the reported target ( Coates et al, 2019 ).…”

Anisotropic representations of visual space modulate visual numerosity estimation

“…Importantly, while crowding is usually assumed to affect target identification but not detection (Livne & Sagi, 2007;Pelli et al, 2004), recent studies showed that target parts were unnoticed under crowding (Coates et al, 2017;. Such "omission errors" ; see also Melnik et al, 2021) were suggested to be due to "redundancy masking," a recently discovered phenomenon where the number of perceived items in repeating patterns is reduced (Sayim & Taylor, 2019;Yildirim et al, 2020Yildirim et al, , 2021b. Redundancy masking has been shown to occur when as few as 3 items were presented (Sayim & Taylor, 2019;Yildirim et al, 2020Yildirim et al, , 2021b.…”