Motion Perception: Theory and Experiments

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Motion PerceptionTheoryandExperiments
(Pablo J. Velasco) New York University
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Outline

• Goal
• Local cues the aperture problem
• From local to global INTEGRATION
• Hildreths model
• An interesting case the rotating ellipse
• Hildreths model predictions
• Psychophysics experiment
• To do

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What we detectThe aperture problem

• V?
• VII ?

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From local to globalINTEGRATION
Small receptive fields (input) LOCAL information

• (output) GLOBAL perception of motion

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Hildreths model1

• Finding the velocity field
• V V(s)
• compatible with V?

Rigidity
1 Hildreth, E. C., The Measurement of Visual
Motion, The MIT Press, Cambridge, MA (1983)
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Hildreths model

• Assumptions (constraint)

Smoothness

• Q

(Minimize)
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Bayesian model2

• Probabilistic (Bayes rule)

Slowness
(Only translation)

• Probability

(Maximize)
2 Weiss, Y et al., Nature Neuroscience, 5, 598
(2002)
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Ellipse Rotating

• Ambiguous stimuli ? illusions

Change of perception with ellipse eccentricity e
Give info about integration of local into global
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What does Hildreths model predict?

• V minimum Q

QROT
QDEF
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Experiment description

• Goal for a given e, find l.
• Present ellipse (e) rotating (2.5 sec).
• Add a bead on surface, rotating with a given
  ltrial.

• Report whether the bead rotates faster or slower
  than the ellipse.

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Experiment description
l

• Psychometric function l for each e

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(Preliminary) results

• Subject 1

Subject 2
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To do

• Finish the psychophysics (capturing)

• Bayesian model
• 2D cues...