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Measuring Attention and Visual Processing Speed by Model-based Analysis of Temporal-order Judgments
Published on: January 23, 2017
Differential processing: towards a unified model of direction and speed perception
Max Farrell-Whelan1, Kevin R Brooks
1Department of Psychology, Macquarie University, Sydney, New South Wales 2109, Australia.
Vision Research
|September 3, 2013
Summary
Visual perception illusions reveal how the brain processes motion. A static line distorts perceived speed and direction of moving dots, suggesting a unified model for velocity misperception.
Area of Science:
- Visual perception
- Motion perception
- Psychophysics
Background:
- Previous studies identified the statically-induced direction illusion (SDI), where perceived dot direction shifts away from a static line's orientation.
- The SDI's magnitude varies with the angle between the line and dot motion direction.
Purpose of the Study:
- To investigate the effect of static line orientation on perceived velocity of random-dot stimuli.
- To propose and test a unified formal model explaining both direction and speed misperceptions in the SDI.
Main Methods:
- Two experiments using random-dot stimuli moving in the presence of an obliquely oriented static line.
- Systematic variation of the angle between the static line and dot motion direction.
- Psychophysical measurements of perceived direction and speed.
Main Results:
- A novel effect: perceived speed decreases as the angle between the static line and dot motion reduces from 90° to 0°.
- The model successfully accounted for angular repulsion in motion direction and predicted speed changes.
- Different best-fit ratios for direction and speed suggest distinct processing or measurement artifacts.
Conclusions:
- Both direction and speed illusions likely arise from differential processing of object-relative and non-object-relative velocities.
- A unified model with a single free parameter quantitatively explains the observed velocity misperceptions.
- Discrepancies in fitting ratios may stem from psychophysical procedure differences for direction versus speed measurement.
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