week 6 Flashcards
motion processing, chapter 8
importance of perceiving motion
- interacting with dynamic objects
- predator prey dynamics, getting information
- time the arrival of incoming objects, move accordingly
- driving, crossing the street, playing sports, seeing dangers
challenge of assessing motion while moving
- hard to distinguish between self movement (walking, moving your head) and motion of external objects in the visual field
corollary discharge theory
- enhances motion perception
- integrates feedback from eye muscles with visual head motion information to assess object movement
- factors in motion of the eyes, head and body
function of area V5/MT in motion perception
- processing global motion, eg entire objects, input from V1 and V2
- sensitive to motion coherence and direction
- region in the occipital cortex critical for motion perception
- active in motion related visual imagery even without actual motion
3 dimensions of our visual system perceiving motion
- directly ahead, to the sides, above/below us
motion threshold
- minimum speed at which we can perceive an object’s intensity
- if something exceeds our motion threshold it becomes a blur/invisible
- closer objects moving slowly easier to detect
- influenced by brightness, size, visibility time
peripheral vision affect on motion perception
- peripheral vision has lower (better) motion thresholds than foveal vision
- detect motion in our surroundings better
real motion
- the continual change in the position of an object relative to the frame of reference
apparent motion
- illusion of movement created by a sequence of still images
- eg animation
beta motion
- stationary images presented rapidly in succession are perceived as continuous motion
motion
- change in position over time
beta vs phi motion
- beta= perceived motion is indistinguishable from real motion
- phi motion= shows individual elements
correspondence problem
- how the visual system knows if an object seen at Time 1 is the same object at Time 2, eg tracking birds
induced motion
- illusion where a moving object causes another stationary object to appear as if it’s moving
amacrine cells
- cells in the retina sensitive to motion
M Pathway in motion perception
- codes for motion in V1 and along the dorsal stream of vision
P Pathway role in motion perception
- allows us to perceive moving objects in color
reichardt detector
- two adjacent photoreceptors sending signals to a motion sensitive neuron, responds when the impulses arrive simultaneously
- circuits detect different speeds of motion from delays in signals
- struggles to explain motion perception when the observer and object are in motion
where are motion sensitive neurons found in the human visual system
- V1, tuned to specific direction and speeds
saccades
- rapid eye movements, looking from one object to another
- during vision is suppressed, no new information until it ends
smooth pursuit eye movements
- voluntary movements used to track moving objects
real motion neurons vs other motion sensitive neurons
- real motion neurons, respond to object motion not movement caused by eye movements
motion aftereffect
- motion-based illusion, stationary object moves in the opposite direction of real or apparent motion just observed
what are N-I and N-r neurons sensitive to?
N-I upward motion
N-R downward motion
what happens when N-I neurons stop firing after prolonged stimulation
- the inhibition of N-R neurons is lifted, perception of motion in the opposite direction
point light display
- lights attached to joints, motion is filmed in darkness
- can infer human form and emotion
optic flow patterns
gradient of flow
- the difference in perceived speed of objects moving past us as we move forwards and actual speed
optic flow
expansion
- point in the distance where the gradient of flow comes to zero
affordance
- information in the visual world that specifies how information can be used
- eg hurdle affording jumping
optic flow patterns
- how objects in our field of vision appear to move relative to us
- nearby objects seem faster vice versa
- provide information about distance and speed
- increase speed, gradient of flow accelerates, nearby objects appear to move faster, pilots
lateral intraparietal responsible for
- control of eye movements
medial intraparietal responsible for
- planning and controlling arm movments
anterior intraparietal responsible for
- grasping objects
micro saccades
- small rapid eye movements that occur even when fixating on an object
visual fading
- loss of visual experience when neither the eyes or visual world are moving
benefit of studying motion illusions
- reveal how our perceptual systems work by showing where they fail
akinetopsia
- unable to perceive motion
