Bounded contribution of human early visual cortex to topographic bias in spatial extent perception
Poster No:
1332
Submission Type:
Abstract Submission
Authors:
Juhyoung Ryu1, Sang-Hun Lee1
Institutions:
1Seoul National University, Seoul, South Korea
First Author:
Co-Author:
Introduction:
Accurate perception of object's spatial extent, an enclosed region they occupy in space, is crucial for successful interaction with the environment. The topographic representation of space in the early visual cortex (EVC) has been favored as a neural correlate of spatial extent perception. However, it remains mostly unexplored whether and how the topographic anisotropies in EVC relate to those in perceived spatial extent. In this study, we examined the topographic representations of the EVC and individuals' perception, focusing on the influence of orientation (co-axiality) and radial position (radiality) of stimuli: radial when elongated along the radial axis on which the RF is positioned in retinotopic space, and co-axial when elongated along the axis aligned to the stimulus orientation in visual space. We conducted fMRI and psychophysics experiments to examine the dominant factor in topographic bias of the pRF and perceived anisotropy and the relationships of anisotropies between the pRF and perception at the individual level. The results revealed a mismatch in bias, with EVC showing a radial bias and perception showing a co-axial bias. Despite of this mismatch, inter-individual variabilities in EVC's anisotropy were correlated with that in perception. The results suggest the involvement of additional mechanisms beyond EVC in transforming information to match perceived spatial extent.
Methods:
we estimated the pRFs of individual voxels in EVC using visual stimuli with two types of gratings with different orientations in the retinotopic polar space: radially and tangentially oriented gratings (Fig. 1c, 2a-1). Due to the correlation between preferred orientations and polar-angle positions of neurons (Fig. 1a,b), how the two anisotropy factors affect the pRF anisotropy is inconclusive. To overcome this, we used radially and tangentially oriented gratings, decorrelating orientation and polar-angle position. By inspecting elongation axes in tangential orientation condition, the study distinguishes whether co-axiality or radiality dominates. Furthermore, comparing degrees of elongation between stimulus orientations reveals the modulatory influence of the non-governing factor (Fig. 1e,f).
·Figure 1. The rationale for pRF estimation using radially and tangentially oriented gratings to evaluate the respective influences of topographic factors on the spatial representation of EVC.
Results:
We quantified the degree of radial elongation with the radial bias index, RI_pRF, derived from the subtractive contrast between the radial and tangential spatial extents of the pRFs. We found that radiality is the dominant factor governing the pRF anisotropy, with pRFs extending farther along the radial axis than the tangential axis, regardless of the stimulus orientation conditions (Fig. 2b). RI_pRF tended to be smaller in the tangential orientation condition than in the radial orientation condition for all three areas of EVC, indicating that the pRF spatial extent is radially biased, with a weak modulation by co-axiality, albeit statistically insignificant. Next, we acquired psychophysical data and estimated radial bias index of the perceived anisotropy, RI_perc, from the observers whose pRF anisotropy was estimated. The perceptual anisotropy is co-axially biased with radial modulation (Fig. 2c). Despite of the mismatch in anisotropy between EVC and perception, there were the substantial inter-individual correlations in the influence of radiality and co-axiality on both the pRF and perceptual anisotropies (Fig. 2c,e).
·Figure 2. FMRI and psychophysical experimental design (a), a mismatch in bias and co-variations in the inter-individual difference between the pRF anisotropy and the perceptual anisotropy (b-e).
Conclusions:
Our study highlights a mismatch in bias between the pRF of EVC and perceived anisotropies, with inter-individual correlation between them, suggesting a limited role for EVC in spatial extent perception. The findings implicate that spatial extent perception builds on EVC's spatial representation but requires an additional mechanism to transform its topographic bias.
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI) 1
Perception, Attention and Motor Behavior:
Perception: Visual 2
Keywords:
Computational Neuroscience
FUNCTIONAL MRI
Perception
Vision
1|2Indicates the priority used for review