Training-Induced Changes in Radial–Tangential Anisotropy of Visual Crowding

Abstract

One of the diagnostic features of visual crowding, radial-tangential anisotropy, has been observed both in behavioral experiments as well as in responses of the blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal. As has been shown previously, crowding is stronger for radially arranged flankers, and this tendency is reflected in BOLD signal suppression. In the current study, we examined the effect of practice on the neural correlates of crowding. We expected that training on a crowding task would cause shrinkage of the crowding zone that would be mirrored in corresponding BOLD signal responses. Methods: Pre-and post-training fMRI images were acquired in 17 healthy volunteers using a 3-tesla MRI scanner. Participants were trained over 4 consecutive days on a crowding task. Results: Comparison of the pre-and post-training behavioral data indicates a significant shrinkage of the crowding zone as a result of training. Moreover, we observed a pronounced radial-tangential anisotropy in the BOLD signal prior to training; that is, radial flankers induced a larger reduction in the BOLD signal compared to equally spaced tangential flankers. After training, this radial-tangential anisotropy in the BOLD signal was significantly reduced. Specifically, we found significant changes in BOLD responses for the radial flanker configuration. Conclusions: Our results demonstrate that training-induced changes in the anisotropic shape of the crowding zone are reflected in the BOLD signal in the early visual cortex. Translational Relevance: Perceptual learning tasks may have the potential to improve visual performance by promoting neural plasticity. Our results could motivate the development of suitable rehabilitation protocols for patients with central vision loss.

The Bouma law accounts for crowding in fifty observers

“…To estimate the reliability of our measurements we acquired each threshold twice. Previous work showed improved performance in crowding tasks for repeated measurements (Chung, 2007; Malania et al, 2020). From their figures we estimate the second-block benefit to be 13% for Malania et al and 20% for Chung.…”

Transient attention equally reduces visual crowding in radial and tangential axes

“…However, no study, to our knowledge, has tested the effect of attention manipulation on the spatial extent of radial crowding. Moreover, although one study demonstrated reduction of the radial–tangential anisotropy by learning ( Malania, Pawellek, Plank, & Greenlee, 2020 ), no study has investigated whether and how spatial attention reduces the radial–tangential anisotropy of crowding.…”

Dissecting (un)crowding

“…Fifth, we reproduced the previous finding that the mutual crowding of the squares increases with the number of flanking squares ( Manassi et al, 2013 ). In addition, we found a radial-tangential anisotropy ( Chung, 2013 ; Greenwood et al, 2017 ; Kwon et al, 2014 ; Malania et al, 2020 ; Toet & Levi, 1992 ). The target square in the horizontally aligned squares was more crowded than in the vertically aligned squares ( Figure 5 & Supplementary Figure S1 ).…”

“…Crowding has specific characteristics. For example, flankers in the radial orientation interfere stronger than flankers in the tangential orientation (radial-tangential anisotropy; Chung, 2013 ; Greenwood, Szinte, Sayim, & Cavanagh, 2017 ; Kwon, Bao, Millin, & Tjan, 2014 ; Malania, Pawellek, Plank, & Greenlee, 2020 ; Toet & Levi, 1992 ), which was explained by elliptic receptive fields in early visual areas ( Hubel, Wiesel, & Stryker, 1978 ; Silson, Reynolds, Kravitz, & Baker, 2018 ; Toet & Levi, 1992 ) or by an uneven sampling density in the early visual cortex ( Kwon & Liu, 2019 ; Motter & Simoni, 2007 ).…”