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Motion sharpening and contrast: gain control precedes compressive non-linearity?
Stephen T Hammett1, Mark A Georgeson, Samantha Bedingham
1Department of Psychology, Royal Holloway College, University of London, Egham, Surrey TW20 0EX, UK. s.hammett@rhul.ac.uk
Vision Research
|April 23, 2003
Summary
Motion makes edges appear sharper. This study found that while motion sharpening increases with speed, it remains largely unchanged by contrast levels, challenging previous models.
Area of Science:
- Visual perception
- Computational neuroscience
- Image processing
Background:
- Perceived edge blur is reduced in moving stimuli compared to static ones.
- Previous models suggested a speed-dependent compressive transducer explains motion sharpening.
- These models predicted sharpening should increase with contrast.
Purpose of the Study:
- To investigate the relationship between contrast and motion sharpening.
- To test the predictions of existing models regarding contrast invariance.
- To develop an improved model that accounts for observed results.
Main Methods:
- Experimentally measured the sharpening of periodic patterns across various contrasts, blur widths, and speeds.
- Compared empirical data with predictions from a local contrast transducer model.
- Proposed and evaluated a revised model incorporating dynamic contrast gain control.
Main Results:
- Motion sharpening significantly increased with stimulus speed.
- Sharpening was found to be practically invariant with respect to contrast.
- The contrast invariance contradicted predictions of models relying solely on static non-linearities.
Conclusions:
- A static compressive transducer alone cannot explain the contrast invariance of motion sharpening.
- Incorporating dynamic contrast gain control preceding the transducer accurately predicts motion sharpening, its speed dependence, and contrast invariance.
- This suggests a more complex, dynamic mechanism underlies motion-induced edge sharpening in visual perception.