Motion perception

Where pathway

Dorsal stream in the parietal lobe

About the perception of moving objects and locating objects in space

V1 —> V2 —> V5/MT (perceiving movement) —> Posterior partiel cortex (locating objects in space)

Function of motion perception

Detect things

Perceiving objects

Social perception

Taking action

Types of perceived motion

Real vs illusory

3 types of illusory motion

Apparent motion, induced motion, and motion aftereffects

Apparent motion

Illusion of motion or change in size of a visual stimulus

Ex: ticker tape signs or “flip books” or stop motion

Induced motion

When motion of one object (usually the large one) causes a stationary stimulus appear to move

nearby objects

Motion aftereffects

When viewing a moving stimulus causes a stationary stimulus to appear to move

Can occur when viewing the moving stimulus and then viewing the stationary stimulus

Biological motion

Movement of biological organisms

Representational momentum

From still pictures implying movement

Optic array

Structured pattern of light created by the presence of objects, surfaces, and textures in the environment

Local disruption of the optic array

Occurs when one object moves relative to the environment, so the stationary background is covered and uncovered

V5/MT (middle temporal) gyrus

Direction and speed of motion, representational momentum

Medial Superior Temporal Area

Processing optic flow, locating and reaching for moving objects

Larson et al (2006)

fMRI study of motion perception

Two conditions: (1) control condition - visual squares, (2) real motion - square moved back and forth, (3) apparent motion - squares flashed back and fourth

Methods for studying motion perception

Dot displays

Coherence - dot displays

The degree the dots move in the same direction

Lesions to the brain - V5/MT

Movement agnosia or akinetopsia - impaired ability to perceive moving objects

Stimulate the brain - V5/MT

Transcranial magnetic stimulation is noninvasive stimulation of the brain - in humans

Microstimulation or direct stimulation of the brain - is invasive

Point-light walkers

A method for studying biological motion by placing lights on the joints of people moving and recording the light

Newsome et al (1995)

Studying monkeys MT activity and dot displays

Stimulus = used dot displays with varying coherence

Results: as dot coherence increased

• Behavior: judged direction of the motion was more accurate

• Physiology: MT neurons fired more frequently

Grossman & Blake (2001)

Biological motion and the STS

Task-based fMRI

Stimuli used - point-light walkers and scrambled point motion

Results: STS had more activity when viewing biological motion than scrambled point motion