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Pattern discrimination with increment and decrement Craik-Cornsweet-O'Brien stimuli
1McGill Vision Research Unit, Department of Ophthalmology, Montreal, Quebec, Canada.
Spatial Vision
|January 1, 1996
Summary
Induced brightness in Craik-Cornsweet-O'Brien (CCOB) figures shows a polarity difference, but contrast thresholds for discriminating CCOB stimuli do not. This suggests receptive field size differences are not the cause of this brightness perception asymmetry.
Area of Science:
- Visual perception
- Computational neuroscience
- Psychophysics
Background:
- Craik-Cornsweet-O'Brien (CCOB) figures exhibit greater induced brightness for decrements than increments.
- This asymmetry was previously attributed to differences in On-centre and Off-centre receptive field sizes.
Purpose of the Study:
- To investigate if receptive field size differences explain the polarity asymmetry in CCOB induced brightness.
- To test if increment and decrement discrimination thresholds for CCOB stimuli differ from their step-edge equivalents.
Main Methods:
- Contrast thresholds were measured for discriminating 'cusp' from 'square-bar' stimuli.
- Discrimination tasks were performed for both increment and decrement forms of the stimuli.
Main Results:
- No significant difference was found between increment and decrement discrimination thresholds.
- The findings contradict the prediction that receptive field size differences underlie the observed brightness asymmetry.
Conclusions:
- On- versus Off-centre receptive field size differences are unlikely to explain the polarity-based asymmetry in CCOB induced brightness.
- The magnitude of induced brightness in CCOB figures is not directly paralleled by discrimination abilities from step-edge stimuli.
- Results have implications for understanding brightness coding models in visual perception.