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Published on: February 8, 2020
Brightness and transparency in the early visual cortex
Viljami R Salmela1, Simo Vanni
1Institute of Behavioural Sciences, Division of Cognitive and Neuropsychology, University of Helsinki, Finland. viljami.salmela@helsinki.fi
Journal of Vision
|June 26, 2013
Summary
Neural processes of visual perception are explored. Early visual cortex areas V1-V3 show sensitivity to surface brightness and transparency, suggesting separate neural representations for these distinct visual qualities.
Area of Science:
- Neuroscience
- Visual Perception
- Computational Neuroscience
Background:
- Psychophysical studies demonstrate transparency's significant impact on perceived brightness and lightness.
- Neural mechanisms underlying these perceptual effects, particularly in the early visual cortex, remain largely unresolved.
- Discrepant findings exist regarding the role of the primary visual cortex (V1) in surface brightness representation and the neural locus of transparency perception.
Purpose of the Study:
- To investigate the correlation between functional magnetic resonance imaging (fMRI) responses in human visual areas V1, V2, and V3 and perceived brightness and transparency.
- To differentiate the blood oxygen-level-dependent (BOLD) response related to brightness from responses to local contrast and mean luminance.
- To determine the neural representation of transparency within the early visual cortex.
Main Methods:
- Utilized variants of White's brightness illusion, employing both opaque and transparent stimuli where luminance increments and decrements were balanced to isolate brightness effects.
- Modulated surround luminance sinusoidally (0.5 Hz) to induce brightness modulation in a constant or counter-modulated target surface.
- Calculated mean BOLD signal changes in V1, V2, and V3 corresponding to the retinotopic location of the target surface.
Main Results:
- BOLD responses in V1-V3 were significantly stronger for stimuli inducing brightness modulation compared to those with constant brightness.
- fMRI responses were also stronger for transparent stimuli than for opaque stimuli, albeit with greater inter-individual variability.
- No significant interaction was found between the effects of brightness and transparency on BOLD responses.
Conclusions:
- The early visual areas V1, V2, and V3 are sensitive to both surface brightness and transparency.
- These findings suggest that brightness and transparency are processed and represented separately within the early visual cortex.
- This study contributes to resolving the neural basis of brightness and transparency perception.
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