mar 6 motion mechanisms cont. Flashcards
saccadic suppression
reduction of visual sensitivity that occurs during saccadic eye movements; eliminates smear from retinal image for observer motion (still blur for object motion)
for saccadic suppression, does object or observer motion still have blur present on retinal image?
still blur present on object motion, but for observer motion
3 strategies to distinguish observer motion from object motion
motion scale, saccadic suppression, comparison of image-retina and eye-head signals
motion scale
strategy to tell between object and observer motion; object moves locally but background still the same vs observer moves and can tell cuz large scale movement
visual system compares ______ signals and ____ signals to determine what moves
image-retina; eye-head
retinal movement & eye movement combinations & object movement
object motion perceived when retinal movement & eye movement are opposites (either yes/no, or no/yes)
comparator
centre in brain that receives motion signals from eye-head and image-head retina systems
2 theories of how info about eye movements reaches the comparator
inflow & outflow
inflow (Sherrington)
feedback from proprioceptors in extraocular eye muscles
outflow (Helmholtz)
copy of motor command to extraocular eye muscles (efference copy or corollary discharge)
there is corollary discharge when
trying to move your eyes; copy motor command (willing eyes to move)
paralyzing eyes (no retinal mvt, no feedback, yes corollary discharge) produces motion? supports what theory
yes; supports outflow theory
feedback from eye muscles
eyes actually moving (separate from intent to move eyes); inflow theory
when push eye (no afterimage)
retinal mvt, feedback, no corollary discharge, world moves (supports outflow)
when push eye (afterimage)
no retinal mvt, feedback, no corollary discharge, world doesn’t move (supports outflow)
evidence for inflow (Steinbach)
-proprioceptors in eye muscles
-after 1st strabismus surgery, patients can point accurately; not after multiple when propriocepters removed
-inflow (feedback) for visually-guided pointing
why should eye muscles be different than other muscles (they all work by feedback)?
eyes carry a constant load
real-motion neurons respond to and not as much to
retinal image motion created by stimulus movement, but respond less to motion created by smooth pursuit
predictive remapping
receptive fields of neurons in several cortical areas shift to their future location before a saccade
predictive remapping is physiological evidence for (monkey saccade trials)
corollary discharge; neurons anticipate moving their receptive field and responds before receptive field is actually there; no feedback before a saccade occurs so must come from copy of motor command (outflow)
