MOTION PERCEPTION Types of Motion Perception Corollary Discharge Theory Movement Detectors Motion Perception and Object Perception Ecological Perception Vestibular System

Types of Motion Perception Real Movement occurs when an object actually moves Apparent Movement is a perception of motion caused by the appearance of two stationary stimuli at different times

Types of Motion Perception Induced Movement occurs when movement of one object causes a perception of motion in another object Movement After-Effects occur when a perception of motion is caused by viewing real movement in the opposite direction

Corollary Discharge Theory When the brain sends a message to move the eyes, it sends a copy (corollary discharge) to a comparator Information about image movement is also sent to the comparator

Corollary Discharge Theory If the comparator receives information that the image is moving but the eyes are not moving, motion is perceived If the comparator receives information that the image is not moving but the eyes are moving, motion is perceived

Corollary Discharge Theory If the comparator receives information that the image is moving and the eyes are also moving, motion is not perceived

Movement Detectors Real Movement Detectors in V3 respond only when the stimulus actually moves, whether the eyes are moving or not Neurons in the Medial Temporal (MT) cortex respond to movement in a particular direction

Motion and Object Perception Recognition of patterns affects perception of movement shortest path constraint - movement appears to occur on the shortest possible path When the shortest path violates knowledge about objects, a longer path is perceived

Motion and Object Perception Recognition of motion affects perception of objects Kinetic Depth Effect Biological Motion

Motion and Object Perception The “What” and “How” streams communicate with each other

Ecological Perception How do we use perception to guide our actions in the environment? Invariant information - information that remains constant during observer movement

Ecological Approach (Gibson) We can perceive motion by using information from the environment Optic array - surfaces, textures, and contours in the environment Local disturbance - one object moves relative to the environment, deleting and accreting

Optic Flow Optic flow - movement of elements relative to the observer Focus of Expansion(FOE) - point in the distance at which there is no flow

Navigation Neurons Collision-sensitive neurons - respond only when an object is on a collision course; found in pigeon brain Neurons in the human Medial Superior Temporal (MST) area respond to flow patterns; have large receptive fields

Mirror Neurons Located in Premotor Area (PM) in frontal lobes Respond when the monkey grasps an object OR when the monkey sees someone grasp an object

Vestibular System This system provides information to the brain on orientation and movement of body The sensory organs are the semicircular canals and vestibular sacs in the inner ear

Semicircular Canals three tubes at right angles fluid filled hair cells at the base of each canal detect rotation in three dimensions

Vestibular Sacs two sacs at the base of semicircular canals detect linear motion motion causes movement of statolith which bends hair cells

Vestibular Pathway 8th Cranial nerve carries information from hair cells brain stem cerebellum (movement and balance) thalamus cortex

Interaction with Vision Vestibulo-ocular Reflex - stabilizes visual field by coordinating eye movements with head movements Motion sickness - mismatch between visual and vestibular information

Interaction with Vision Visual cues can affect balance, overcoming influence of vestibular information Swinging room experiment (Lee & Aronson)