Functions of Movement Perception

survival in environment prey and predators use to locate movement capturers our attention

real motion

object is physically moving

Illusory motion (apparent movement)

stationary stimuli are presented in slightly different location TVs

Induced motion

other cues, movement of one object results in perception of movement in another object. photo of someone running, blurry, photo of someone about to throw something

motion aftereffect

look at video, video stops, see illusion of movement in opposite direction, imbalance of motion perception

moving objects benefits

gives us more information about the object from motion signals

structure from motion

fish cannot see 3d the way we can they use this, our ability to extract vivid impressions of an object's 3D shape from motion

retina

mosaic of small receptive fields for retinal ganglion cell, Each provides very low-level information, reaching visual cortex signals from multiple small retinal receptive fields are combined into larger receptive fields

Larger receptive fields

generally used to process more complex information as information passes along visual processing pathway

motion

spatial displacement of object(s) over time: a spatial-temporal phenomenon

Visible movement

usually results in corresponding spatial-temporal changes in light patterns on retina - motion perception begins by extracting these patterns

Motion Perception: Retinal Information

output unit is direction selective

Motion Perception: Retinal Information, other direction

not enough signals to say there is motions

Motion direction processing

speed or villosity preferences in output units, low level motion

Wertheimer (1912)

Found that the delay between frames determines if motion is perceived apparent motion perception even if one stimulus is presented to one eye and other is presented to other eye, Signals from two eyes segregated until reaching visual cortex → DS neurons must be located somewhere in cortex

Fooling motion detectors

motion perception, real and apparent, involves DS neural mechanisms something like those proposed by Reichardt If (time delay) and (spatial difference) associated with DS neurons correspond to spatial separation and presentation delay between stimuli, DS neurons will signal motion or DS neuron apparent and real motion constitute equivalent events

Larsen et al Comparison of Real and Apparent Motion

Control condition: each dot activated a separate area of visual cortex. Apparent and real motion: activation of visual cortex from both sets of stimuli was similar perception of motion in both cases is related to same brain mechanism.

corollary discharge theory explains 3 conditions

An object moves, and observer is stationary An object moves, and observer follows object with their eyes An observer moves through a stationary environment

corollary discharge theory

information is sent off to other brain parts to better process the visual information

Image displacement signal

movement of image stimulating receptors across retina

Motor signal

signal sent to eyes to move eye muscles

Corollary discharge signal

split from motor signal, predictive neural signal from motor system

Corollary Discharge Theory - Physiological Evidence

Damage to medial superior temporal area in humans: perception of movement of stationary environment with movement of eyes. Real-movement neurons found in monkeys respond only when a stimulus moves and do not respond when eyes move

Firing and coherence experiment, Newsome et al

As coherence of dot movement increased, firing of MT neurons and judgment accuracy also increased middle temporal lobe

Motion Perception in the Brain

Aperture problem

observation of small portion of larger stimulus leads to misleading information about direction of movement# Viewing only a small portion of a larger stimulus can result in misleading information about the direction in which the stimulus is moving.

Aperture problem: role of MT

outputs from V1 directionally selective neurons are integrated to form unified, coherent motion MT receptive fields up to 10 times larger than V1, suggesting array of spatially distributed V1 neurons contribute to synthesis of individual MT receptive fields directional selectivity of MT neurons differs from that of V1 neurons they receive signals from

Movshon et al. (1986)

Recorded activity of V1 neurons sensitive to one of two orthogonal directions MT appears to be capable of pooling the local motion signals it receives from V1 and calculating a separate pattern motion

Motion aftereffect: role of MT

activity in V5/MT during stationary period, which gradually reduced, mirroring psychophysically measured MAE (V5, 5th visual area) just a correlation

Structure from motion: role of MT

MT cell most active when perceived rotation direction matched cell’s preferred direction, less active when perceived direction reversed

Biological motion

motion events that distinguish animate from inanimate objects – a specific category of structure- from-motion

Motion and the Human Body, Grossman et al.

dots on people while moving vs random dots Noise was added to dots so they could only achieve 71% accuracy. Transcranial magnetic stimulation applied to Superior Temporal Sulcus (STS) decreased ability to detect biological motion

Striate Cortex (V1)

Direction of motion across small receptive fields

Middle Temporal Area (MT)

Direction and speed of object motion

Medial Superior Temporal Area (MST)

Processing optic flow; locating moving objects; reaching for moving objects

Superior Temporal Sulcus (STS)

Perception of motion related to animals and people (biological motion

Motion Preference Amongst Newborn Babies, Vallortigara et al (2005)

Perception of biological motion may not depend on visual experience, may be innate

Motion Responses to Still Pictures – implied motion

Areas of brain responsible for motion perception fire in response to pictures of implied motion