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Lateral modulation of contrast discrimination: flanker orientation effects
Chien-Chung Chen1, Christopher W Tyler
1The Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA. chen@ski.org
Journal of Vision
|April 8, 2003
Summary
Adjacent stimuli orientation significantly impacts visual contrast discrimination. Flankers can either facilitate target detection or enhance pedestal masking, depending on contrast and orientation tuning.
Area of Science:
- Visual perception
- Computational neuroscience
- Psychophysics
Background:
- Contrast discrimination is fundamental to visual processing.
- The influence of surrounding stimuli (flankers) on target perception is complex.
- Understanding orientation effects in visual masking is crucial for visual models.
Purpose of the Study:
- To investigate how flanker orientation affects contrast discrimination.
- To differentiate between threshold facilitation and pedestal enhancement.
- To model the underlying neural mechanisms using a sensitivity modulation approach.
Main Methods:
- Employed a dual-masking paradigm with Gabor stimuli.
- Varied flanker orientation from parallel (0 degrees) to orthogonal (90 degrees) to a vertical target.
- Fitted experimental data using a computational model of sensitivity modulation.
Main Results:
- Flankers showed orientation-tuned threshold facilitation at low pedestal contrasts.
- Pedestal enhancement by flankers was largely orientation-invariant at high pedestal contrasts.
- The sensitivity modulation model explained these effects by modulating excitatory and inhibitory inputs.
Conclusions:
- Flanker orientation critically influences visual contrast discrimination through distinct mechanisms.
- Pedestal enhancement occurs when flanker facilitation is stronger for the pedestal than the target.
- The orientation-dependent effects require considering both individual modulation factors and their ratios.