chapter 8-motion perception Flashcards
computation of visual motion
motion detector; change in position, two adjacent receptors registers change, a delay accounts for change in time
motion is
change in position over time; activate receptive field at 2 different locations; 2 points in time in sequence
detecting movement (diagram) is what kind of circuit
neural motion detecting circuit
two input neurons with adjacent receptive fields feed into a
comparator neuron
during stimulation with motion, the two inputs are stimulated at ___ times
different
for rightward motion, their responses arrive at the comparator ____
together
evidence for motion detectors in ___ recordings
single cell
evidence for motion detectors because
many cells in cat and monkey visual cortex are direction selective, and respond very well to single direction
direction selectivity
responds well to 1 direction of motion much better than others, especially the opposite
MT
higher level motion selective area; depth; signal motion at larger distances; broader range, larger receptive field
motion after effect
adapt to direction/pattern of motion, perceive opposite afterwards; illusion of motion of a stationary object that occurs after prolonged exposure to a moving object; motion opponent process; interocular transfer
what accounts for the motion after effect
classic opponent process; motion is seen in te direction of the team that wins
with stationary pattern, is there motion seen
no, only moderate activity
with motion in one direction, what are the neurons doing
neurons are selective for that direction, winning but fatiguing
after adaptation and in presence of stationary pattern, what happens
perceive motion in opposite direction
retinal image motion comes from what
movement of object in the world or movement from observers head/body/eyes
moving car, stationary eye; leftward object motion results in right
displacement on the retina
stationary car, moving eye; when you shift your gaze,
location of objects move on retina, but occulomotor muscles signal eye movement
observer motion
move eye/head/body and retinal image changes
optic flow
changing angular positions of points in a perspective image that we experience as we move through the world; local velocities on the retina inform about motion; motion in depth, low velocities in the center, high velocities in the periphery
eye movement commants
motor system tells eyes to change position
saccadic suppression
the reduction of visual sensitivity that occurs when we make saccadic eye movements; eliminates the smear from retinal image motion during an eye movement
smooth pursuit
eye smoothly follow a moving target
saccade
rapid movement of the eyes that changes fixation from one object or location to another; jumps; 7-9 letters, 15 to the right and 3-4 to the left
vergence
two eyes move in opposite directions, as when both eyes turn toward the nose
reflexive
automatic and involuntary eye movements; eyes move to compensate for turning head/body so that eyes will stay focused on point
mystagmus
eye jitters
optokinetic nystagmus
jerk in the direction of motion when trying to fixate
real movement
continuous change in position in a natural image
apparent movement
discontinuous change in positions (series of locations); rapid alteration of objects
distance time trade off
when objects are close together, can be fast flicker and see motion, as distance increase time delay must increase also
receptive field size grows as you get __ in visual system
higher up
good apparent movement is
indistinguishable from real movement
cortical direction selective cells respond to
apparent movement
apparent movement ___ neural detectors in the ___ way as real movement
excites, same
the aperture problem
the fact that when a moving object is viewed through an aperture, the direction of motion of a local feature or part of the object may be ambiguous
aperture
opening that allows partial view of an object
what cells have the aperture problem
V1
with aperture, ___ is ambiguous
local motion
if motion within aperture is ambiguous, how does visual system correctly perceive overall motion
motion info from several local apertures (RFs) combines to determine the global motion; whichever possible motion is the same for all apertures
combining info from different apertures happens where
MT
biological motion
pattern of movement of living things
tau
info in the optic flow that could signal time to collision without the necessity of estimating absolute distances or rates
distinctions between processes
short range vs long range
first vs second order
feature tracking
first order
change in position of luminance defined objects
second order
object defined by changed in contrast or texture; focus of expansion
feature tracking
motion perception for any stimulus where a change in position occurs, happens slowly
some neurons are ___ selective motion detectors
directionally
brain uses several strategies to distinguish between __ and __ motion
object and observer
___ motion can be explained by responses in neural motion detectors
apparent
issues about ambiguous local motions are solved with ____
global motion detectors
evidence indicates that 2 or more subsystems mediate motion perception
2
correspondence problem
in binocular vision the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye; in motion detection, the problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a feature in frame 1
