Movement Perception

2. Velocity transposition Movement Perception Physiology Magno cells and tectopulvinar Hubel & Weisel: movement detectors in cortex V3 (local) and V5 (global) Is there anything else to talk about? Activation of movement detectors can’t be all there is with regard to movement perception because of three things: 1. Thresholds 2. Velocity transposition 3. Movement perception doesn’t require retinal movement, and retinal movement doesn’t always result in perceived movement

Why movement detector activity alone cannot be the whole story of movement: 1. Thresholds Threshold: 1/6-1/3 of a degree per second Threshold: upwards of 1/60th of a degree

2. Velocity transposition Why movement detector activity alone cannot be the whole story of movement: 1. Thresholds 2. Velocity transposition

2. Velocity transposition Why movement detector activity alone cannot be the whole story of movement: 1. Thresholds 2. Velocity transposition 3a. “real” movement perception doesn’t always require retinal movement, and 3b. retinal movement doesn’t always result in movement being perceived The Perception of “real” movement Three different Real movement examples requiring an explanation: 1. Eyes stationary, something “out there” moves 2. Eyes move, but nothing in the environment moves 3. Eyes move to track a moving object How does the brain sort all of this out?

Corollary Discharge Theory -brain tracks two sources of information in determining if movement is perceived: 1) Whether or not movement occurred on the retina, and 2) Whether or not a movement command was sent to the eyes Corollary discharge Movement on the retina Comparator If the input signals are different, “movement” will be perceived by the comparator.

Corollary Discharge Theory e.g.1: eyes stationary, and something moves through visual field Corollary discharge Movement on the retina Comparator

Corollary Discharge Theory e.g.1: eyes stationary, and something moves through visual field Corollary discharge Movement on the retina Comparator Movement is perceived

Corollary Discharge Theory e.g.2: eyes scan around, but nothing is moving in environment Corollary discharge Movement on the retina Comparator No movement perceived

Corollary Discharge Theory e.g.3: tracking a moving object For the object being tracked: Corollary discharge Movement on the retina Comparator Movement perceived

Corollary Discharge Theory e.g.3: tracking a moving object For the background: Corollary discharge Movement on the retina Comparator No movement perceived

Apparent Movement

Apparent movement summary: ISI < 20 msec: simultaneous ISI 40-60 msec: looks ‘real’ ISI 60-200 msec: phi phenomenon ISI > 200 msec: little movement perceived The above is the result of a primitive low-level movement system Evidence of a high-level system: ‘long-range’ and complex stimuli require longer ISIs

Two-object apparent motion

Apparent movement of complex stimulus: 20 msec

Apparent movement of complex stimulus: 300 msec

Induced Movement: basic

Vection

Vection

Vection

Vection

Vection

Autokinetic Movement

Motion aftereffect (waterfall illusion)

Biological motion