Abstract
PurposeOne 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.MethodsPre- 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.ResultsComparison 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.ConclusionsOur 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 RelevancePerceptual 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.
Highlights
The visual environment we live in has an excessive complexity and contains multitudes of elements; our visual system often faces the challenge of identifying an object within clutter
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
Our results could motivate the development of suitable rehabilitation protocols for patients with central vision loss
Summary
The visual environment we live in has an excessive complexity and contains multitudes of elements; our visual system often faces the challenge of identifying an object within clutter. The inability to recognize an object when it is surrounded by flanking objects is referred to as visual crowding.[1,2,3] Crowding is considered to be the main bottleneck of object recognition in the periphery and it sets limits to visually guided actions, reading, and other tasks of everyday life. The neural mechanisms of crowding have been extensively discussed, many aspects of crowding remain largely unresolved. Crowding shares some similarities with masking phenomena, it differs in several important ways; for example, the extent of crowding depends on eccentricity whereas masking does not.[4,5] The current belief is that crowding results from some sort of spatial pooling that occurs in peripheral vision.[2,5] The nature of this pooling is not precisely known, and several different mechanisms have been proposed, such as averaging,[6] population processing,[7] or summary statistics.[8,9] Another popular
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