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Cross-Modal Multivariate Pattern Analysis
Published on: November 9, 2011
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Distinct patterns of surround modulation in V1 and hMT
Gorkem Er1, Zahide Pamir1, Huseyin Boyaci2
1A.S. Brain Research Center, National Magnetic Resonance Research Center (UMRAM), Neuroscience Graduate Program, Bilkent University, Ankara, Turkey.
Neuroimage
|July 7, 2020
Summary
Surround modulation in the visual system differs between the primary visual cortex (V1) and middle temporal complex (hMT+). This difference, particularly in hMT+, explains how contrast affects motion perception as stimulus size changes.
Area of Science:
- Neuroscience
- Visual Perception
- Computational Neuroscience
Background:
- Surround modulation, where stimuli outside a neuron's receptive field influence its response, is crucial for visual processing.
- Understanding differences in surround modulation across cortical areas and their interactions remains an open question.
- Previous research highlights a size-contrast interaction in motion perception: larger stimuli improve low-contrast direction discrimination but impair high-contrast discrimination.
Purpose of the Study:
- To investigate the distinct patterns of surround modulation in the primary visual cortex (V1) and the middle temporal complex (hMT+).
- To link these neural activity patterns to the perceptual size-contrast interaction observed in motion discrimination tasks.
- To evaluate the predictive power of the divisive normalization model for these observed phenomena.
Main Methods:
- Behavioral experiment replicating the perceptual size-contrast effect using drifting gratings of varying sizes and contrasts.
- Functional magnetic resonance imaging (fMRI) to measure cortical responses in V1 and hMT+ under identical stimulus conditions.
- Application of the divisive normalization model to predict neural activity patterns.
Main Results:
- Behavioral experiments confirmed the perceptual size-contrast interaction.
- fMRI data revealed that V1 responses increased with stimulus size at both low and high contrasts.
- In contrast, hMT+ responses increased with size at low contrast but remained unchanged or decreased at high contrast, mirroring perceptual performance.
- The divisive normalization model successfully predicted these distinct activity patterns in V1 and hMT+.
Conclusions:
- Surround modulation mechanisms differ significantly between V1 and hMT+.
- The observed size-contrast interaction in motion perception is likely rooted in the activity of hMT+.
- The divisive normalization model provides a unifying framework linking neural activity and perceptual outcomes in the context of surround modulation.
