The Role of Transient Attention in the Radial-tangential Anisotropy of Crowding

Kewan-Khalayly, Bahiyya; Migó, Marta; Yashar, Amit · 2021 · Crossref

DOI: 10.21203/rs.3.rs-822115/v1

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Summary

This study investigates the interaction between transient spatial attention and the radial-tangential anisotropy of visual crowding. Visual crowding, the inability to identify a peripheral object due to nearby flankers, exhibits a radial-tangential anisotropy where critical spacing (the minimum distance required to avoid interference) is larger when flankers are arranged radially (along the line from fixation) than tangentially (perpendicular to that line). While previous research established that transient attention can reduce crowding interference, it remained unclear whether attention modulates this specific anisotropy. The authors hypothesized that if the anisotropy stems from attentional limitations, cueing the target location would improve identification more significantly in radial arrangements than in tangential ones. To test this, sixteen participants performed an orientation discrimination task using a "T" target and two "H" flankers presented at 7° eccentricity. The experimental design manipulated two factors: flanker arrangement (radial vs. tangential) and attentional cueing (valid cue at the target location vs. neutral cue at fixation). Target-flanker spacing varied across eight levels to determine critical spacing thresholds. Eye movements were monitored to ensure fixation, and performance accuracy was fitted with a Weibull function to calculate the critical spacing required for 75% correct identification. The results confirmed that critical spacing was significantly larger in radial arrangements compared to tangential ones, replicating the radial-tangential anisotropy. Furthermore, valid cueing significantly reduced critical spacing and improved accuracy compared to neutral cueing, demonstrating that transient attention alleviates crowding interference. Crucially, however, there was no interaction between cue condition and flanker arrangement; attention reduced critical spacing to the same extent in both radial and tangential conditions. This indicates that while transient attention reduces the overall crowding window, it does not differentially affect the radial versus tangential axes. The findings suggest that transient spatial attention plays an essential role in reducing crowding but is not the mechanism underlying radial-tangential anisotropy. The authors propose that attention enhances spatial resolution by contracting the receptive fields or integration zones of visual neurons, thereby reducing the pooling area that causes crowding. Because this contraction occurs uniformly across radial and tangential axes, it reduces crowding equally in both arrangements. This distinction implies that different processes govern the radial-tangential anisotropy compared to other crowding asymmetries, such as the inner-outer asymmetry, which previous work has linked to attentional locus. These results refine models of spatial vision by separating attentional mechanisms from structural anisotropies in peripheral processing.

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• peripheral attention