Motion Perception

Evolution - predators and prey; other than light or dark, perception of motion is critical for survival
Some 'simple' vertebrates cannot detect objects unless they move
Frog will starve if fly (held still) is put in front of them
In humans, this limitation only at periphery
- cannot detect, identify object in periphery, but can notice its motion and orient to it
Serves attention, 3-D shape, figure-ground segregation, and camouflage breaking functions too
- Akinetopsia or motion agnosia
- Apparent motion (includes stroboscopic motion); movies
- Movement aftereffects like waterfall illusion

Apparent motion
Wertheimer (ISI) if ISI = 30 msec or less - lights on simultaneously
30-60 partial movement of each light
60-200 continuous movement from one point to other

MOVEMENT DETECTORS
- Recall V1's complex & end-stopped cells, responded to moving lines and edges
- Direction Selectivity in Striate Cortex
Motion aftereffect:
Theory: two cells with opposite direction-preferences are paired (A and B) after stimulation to A stops, its firing drops below resting rate; B is at resting rate, but firing is greater than A for a short period

Physio evidence for waterfall illusion
- Barlow & Hill (1963) - Rate of firing in retinal cell after exposure drops below resting rate; stimulation in the null (non-preferred) direction has no effect on cell
- Pasternak (1990) - raised kittens in a strobe environment (8 times/sec)
almost totally eliminated ability to detect direction of a moving stimulus (but not presence)
eliminated 90% of direction-sensitive neurons in striate ctx

Movement Circuits for direction selectivity

STRIATE CTX and MOTION
Albright, Desimone & Gross (1984) - Lesions of striate ctx do NOT eliminate
motion sensitivity in V5 neurons, but DOES if you then destroy Sup Coll
In other studies, lesions = can detect movement but problem in estimating RATE

MEDIAL TEMPORAL CTX and MOTION
Location - located on posterior bank of superior temporal sulcus (STS)
Input - mainly magno system, motion-sensitive cells in layer 4 of V1; V2, V3
lower brain from superior colliculus and pulvinar (in thalamus)
Response of V5 neurons best to moving stimuli regardless of color, shape
Also sensitive / selective for direction of motion
Lesions of V5 = disrupts motion perception / implicated in human motion agnosia
Output - V5 to parietal to inferior temporal ctx (ITC)

May be area of highest analysis, thought to integrate form, depth, and color for perception of 3-D object
In primate, ITC responds best to 3-D objects or photographs of them
Experiments:
Newsome, Britton, & Movshon (1989) - using moving dot displays; monitored MT neurons, with increases in dot correlation:
- monkey judged the direction of movement more accurately
- the MT neurons fired more rapidly
- could even predict monkey's behavior by the firing of a few neurons
In another study, stimulation of directionally sensitive MT cells biased the
response of the monkey to those cell's preferred direction

EYE MOVEMENT
How can the brain tell difference btwn object motion & eye movement ?
Corollary discharge theory: information about the eye movements is provided by signals generated when the observer moves,or tries to move, their eyes
- Motor signal (M) travels from brain to eye muscles to move eyes, image moves across the retina and creates a sensory movement signal (S)
- If S reaches cortex, motion of object perceived
- But if only eyes move, the corollary discharge (C), a copy of motor signal, is transmitted to a hypothetical structure that
gets both C and S, which cancels the S so we don't see object motion which doesn't really exist
Physiological evidence - V3 neurons
- Cells fire if eye stationary and bar moves across retina
- No resonse if bar stationary and eye moves (image moves across retina the same)

AMBIGUITY OF MOTION INFORMATION
Aperture problem: direction of contour's movement thru aperture is ambiguous
The aperture represents a receptive field of a motion detector cell
Could be solved if some cells detect components of movement ("local") while others respond to overall direction of movement caused by a number of components moving in different directions ("global")
If two gratings of similar contrast and velocity are superimposed and moved in different directions, Ss perceive coherent motion, a plaid pattern moving in one direction
Component cells: respond to the direction of movement of single gratings (V1 and MT)
Pattern cells: respond to overall direction of movement of the plaid pattern (found in MT only)

OPTIC FLOW
optic flow pattern: movement of elements in the optic array that occurs as an observer moves through the enviornment
Gibson - focus of expansion: the point in the distance where there is no movement; center of the optic flow and observer's heading
Graziano, Andersen, & Snowden (1994) - neurons in extrastriate area medial superior temporal area (MST) found that respond best to expanding patterns of dots, others that respond to spirals or circular motion

VISION and BALANCE
Balance usually associated with inner ear and vestibular system
Vision has a big role though
Lee and Aronson's Swinging Room - 13-16 month old toddlers in room where
floor is stationary but walls and ceiling swing back and forth
- kids leaned in opposite direction to compensate, wobbled or fell down