PSYC 212 Lecture Notes - Lecture 11: Motion Aftereffect, Mae, Adobe After Effects
6 Nov 2018
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Tuesday, February 13, 2018
1:05 PM
Motion after-effects (MAE)
Motion after-effect (MAE): the illusion of motion of a
stationary object that occurs after prolonged exposure to a
moving object
Existence of MAE implies an opponent process system,
like that of colour vision
§
○
Interocular transfer: the transfer of an effect (such as
adaptation) from one eye to another
Mae exhibits interocular transfer
§
Therefore, MAE must occur in neurons that respond to
both eyes
§
Input from both eyes is combined in area V1, so MAE
must be in V1 or later
§
Recent studies with fMRI confirm that adaptation in MT
is responsible for MAE
§
○
•
First and second order motion
First-order motion: the motion of an object that is defined by
changes in luminance
Luminance-defined object: an object that is delineated
by differences in reflected light
§
○
Second-order motion: the motion of an object that is defined
by changes in contrast or texture, but not by luminance
Texture-defined (contrast-defined) object: an object that
is defined by changes in contrast or texture, but not by
luminance
§
Indicated that the visual system does not simply track
objects' position over time to calculate movement, as
this display demonstrates (since there are no objects to
track!)
§
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Eye movements - seeing is not passive!!!
The displacement on the retina is the same (the cross also
crosses the fovea)
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Why do we perceive the finger to be in motion in the first
case, but perceive the fixation point to be stationary in the
second case? After all, both items moved across our retinas to
the left
Because in the second case there was eye movement
§
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Types of eye movements
Smooth pursuit: voluntary eye movement in which the eyes
move smoothly to follow a moving object
○
Saccade: a type of eye movement, made both voluntarily and
involuntarily, in which the eyes rapidly change fixation from on
object or location to another (3-4 saccades every second)
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Vergence: a type of eye movement, both voluntary and
involuntary, in which the two eyes move in opposite directions
Convergent eye movements turn the eyes inward
§
Divergent eye movements turn the eyes outward
§
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Reflexive eye movements: automatic and involuntary eye
movements
For example, when the eyes move to compensate for
head and body movement while maintaining fixation on
a particular target
§
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Microsaccade: an involuntary small jerk like eye movement
Prevent visual fading
§
Allowing us to see behind the blood vessels in our eye
§
Improve visibility of sharp details
§
Compensate for the sudden loss of acuity a few minutes
outside of the fovea
§
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Control of eye movements
Six muscles are attached to each eye and are arranged in three
pairs
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Controlled by an extensive network of structures in the brain
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Superior colliculus: a structure in the midbrain that is
important in initiating and guiding eye movements
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Different neurons in the SC produce different eye movements
(e.g., left, up, etc.)
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Frontal eye field: a structure in the frontal lobe that is
important in initiating and guiding eye movements
○
Different neurons in the FEF will move the eye to different
spots in space (irrespective of the actual movement required)
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Saccadic suppression: the reduction of visual sensitivity that
occurs when we make saccadic eye movements
Saccadic suppression eliminates the smear from retinal
image motion during an eye movement
§
Ex.: move your eye voluntarily vs by pushing it with your
finger (close the other eye)
§
Ex.: look at yourself in the mirror, fix an eye, then the
other, you don't notice your eyes moving
§
○
Comparator: an area of the visual system that receives one
copy of the order issued by the motor system when the eyes
move (the other copy goes to the eye muscles)
The comparator can compensate for the image changes
caused by the eye movement
§
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Dynamic remapping of receptive fields
A saccade is planned but not yet executed1.
Some neurons in parietal cortex remap their receptive
fields relative to upcoming fixation location
2.
Saccade is executed3.
Receptive fields are already processing information from
new location before eye lands there
4.
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What are these receptive fields?
Eyes are fixated on the fixation point1.
Recording from a neuron in the intraparietal region2.
The neuron fires only if something is presented in the
red circle
3.
Hence, the red circle is the receptive field of that neuron4.
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Attention and scene selection
We can't perceive everything all at once!
Inattentional blindness: a failure to notice--or at least report--
a stimulus that would be easily reportable if it were attended
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Lecture 11
Document Summary
Motion after-effect (mae): the illusion of motion of a stationary object that occurs after prolonged exposure to a moving object. Existence of mae implies an opponent process system, like that of colour vision. Interocular transfer: the transfer of an effect (such as adaptation) from one eye to another. Therefore, mae must occur in neurons that respond to both eyes. Input from both eyes is combined in area v1, so mae must be in v1 or later. Recent studies with fmri confirm that adaptation in mt is responsible for mae. First-order motion: the motion of an object that is defined by changes in luminance. Luminance-defined object: an object that is delineated by differences in reflected light. Second-order motion: the motion of an object that is defined by changes in contrast or texture, but not by luminance. Texture-defined (contrast-defined) object: an object that is defined by changes in contrast or texture, but not by luminance.
