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30 Cards in this Set
- Front
- Back
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1st order motion
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contain shapes defined by luminance difference btwn shape and background
eg. 2 dot apparent motion, global dot motion, plaid motion |
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2nd order motion
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contain shapes defined by variations in texture or contrast w no luminance difference
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3rd order motion
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attentive tracking of moving features (figure vs. ground)
lesions to parietal cortex (dorsal stream) disrupt single & multiple object tracking |
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Provide 3 pieces of evidence that area V5/MT is important for motion perception
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- MT cells respond to larger spatial separations than V1 cells
- MT lesion produced deficits in detecting patch of moving dots - MT lesion produced deficits in choosing fastest moving dots |
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Explain why local motion detectors are unlikely to be found in the human visual pathways before cortical area V1.
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Retinol ganglion cells only respond to on and off in their receptive fields.
V1 neurons most respond to motion, many- particulary complex cells, are direction selective |
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1. Define optic flow
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the changing angular positions of points in a perspective image that you experience as you move through the world
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focus of expansion
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place in visual field with no flow (stationary); all points in flow field seem to emanate from here; indicates direction you are heading
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Discuss 3 ways in which we might use optic flow information for perception.
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- navigating through the environment (FOE provides direction of heading; Warren et al., 1988)
- estimating time to collision (Lee, 1976) (proportional to tau: ratio of retinal image size to rate of image expansion in optic flow field) - posture and balance (Lee & Aronson, 1974) |
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2. Describe the creation of a biological motion stimulus and discuss the neural basis for biological motion perception.
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superior temporal sulcus (STS) important for biological motion
• neurons in monkey STS highly selective for biological motion • fMRI activation for biological walkers vs. scrambled motion • not activated by non-biological motion • lesion here impairs biological motion perception part of dorsal and ventral streams |
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akinetopsia:
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no perception of motion; caused by disruptions to MT; can be side effects of antidepressant medication (example in textbook)
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Riddich's phenomenon
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vision with awareness for fast motion in the absence of primary visual cortex (ML showed normal performance, with awareness of motion,
on a direction discrimination task at speeds above 2 deg/s) |
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eye muscles -
side-to-side rotation |
medial and lateral rectus
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eye muscles-
up/down rotation |
superior and inferior rectus
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eye muscles-
visual axis rotation |
sup/inf oblique
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oculomotor nerve innervates
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medial rectus
superior rectus inferior rectus inferior oblique |
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voluntary eye movements
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saccades
voluntary smooth pursuit vergence |
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saccades
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conjugate eye movements to change fixation
up to 1000 deg/s |
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voluntary smooth pursuit
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conjugate eye movements to track moving objects up to 30 deg/s
- must have moving target to fixate |
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vergence
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disjunctive movements (eye move in opposite directions)
convergence- eyes move together on objects moving closer to viewer - divergence - to fixate on objects moving away from viewer |
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involuntary eye movements
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vestibulo-ocular reflex
optokinetic nystagmus tremor |
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vestibulo-ocular reflex
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controlled by vestibular system
alternating pursuit and saccades in response to body/head motion |
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optokinetic nystagmus
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alternating pursuit and saccades in response to full-field stimulus motion
can induce illusory self-motion (vection |
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tremor
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eye movements during fixation
function to maintain vision (stare at black dot to get after image. Shift to white dot and see jiggling afterimage due to tremor |
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3 general strategies that the brain uses to distinguish between object motion and observer motion.
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motion scale
saccadic suppression visual system compares image-retina and eye-head signals |
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motion scale
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object motion produces localized motion relative to background, observer motion produces large-scale movement patterns across retina
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saccadic suppression
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reduction of visual sensitivity that occurs during saccadic eye movements;
-eliminates smear from retinal image |
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visual system compares image-retina and eye-head signals
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- moving objects stimulate the retina when the eyes are stationary
- movement still perceived when smooth pursuit keeps the retinal image stationary |
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inflow theory
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proprioceptors in eye muscles send feedback
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outflow theory
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motor command centre sends copy of signal to eye muscles (efference copy or corollary discharge)
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evidence for inflow theory
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all other muscles work by feedback
why should eye muscles be different? Steinbach found proprioceptors in eye muscles patients can point accurately after first strabismus surgery (brain knows eye muscles were moved) patients with multiple eye muscle surgeries lose eye position information (proprioceptors removed) neurons in monkey V3 respond to retinal image motion created by stimulus movement, same neurons less responsive to retinal image motion created by smooth pursuit |
