The global slowdown effect: why does perceptual grouping reduce perceived speed?

Area of Science:

• Visual Perception
• Cognitive Neuroscience
• Computational Vision

Background:

• The perception of four rotating dot pairs is bistable, yielding either a local percept of independent rotating pairs or a global percept of translating squares.
• Previous research indicated the global percept moves more slowly than the local percept.

Purpose of the Study:

• To investigate and rule out hypotheses explaining the global slowdown effect in visual motion perception.
• To determine if object size, rotation-specific detectors, or image element reduction during grouping cause the global slowdown.

Main Methods:

• Systematically tested various hypotheses by manipulating stimulus properties.
• Ruled out explanations related to object size differences between percepts.
• Investigated the role of rotation-specific detectors and image reduction during perceptual grouping.

Main Results:

• The global slowdown effect is not caused by the global percept involving larger objects.
• The effect is independent of rotation-specific detectors.
• The global slowdown persists even with stimuli different from the original, suggesting it's not due to image element reduction during grouping.

Conclusions:

• The global slowdown effect in visual perception is likely a general property of perceptual grouping.
• Potential mechanisms include emergent motion signals or increased influence of Bayesian priors toward slow motion due to noisy motion information from grouping.