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Lecture 6

PERCEPTION Lecture 6

8 Pages
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Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier

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PERCEPTION LECTURE 6
eye movements- 6 muscles are attached to each eye and are arranged in three pairs
Inferior/Superior/Lateral/Medial Rectus
Inferior/Superior oblique
Controlled by 3 cranial nerves
Need to tell a person about up down.leftright/ back and forth
3 numbers are necessary for location
Need numbers to describe orientation of object in space 3 numbers
Controlled by extensive network of structures in the brain
Superior Colliculus : structure in the midbrain that plays and important role in initating
and guiding eye movements
2 muscles to rotate an object , 6 muscles in total
Occulomotor nucleus gives rise to occulomotor nerve rect sup , medial rect, inf rect, inferior
oblique
Troclear innervates opposite side superior obliques
Abducens innervates lateral rectus
When stimulated with elec signals, eye movements are observed
Layers involved in motor control, and visual
Eye movements: Smooth Pursuit; eyes move smoothly to follow a moving object
Saccade: Rapid movement of eyes that change fixation from one object or location to another
Vergence Eye Movements: Type of eye movement in which two eyes move in opposite
directions done deliberately
Fixation eye movements, microsaccades
Sometimes not possible to keep eyes fixated
Eyes make counterrotations and need to correct for the rotation of the head
Function of smooth pursuit eye movements,keep object of interest stable and on the fovea
www.notesolution.com
Why do we perceive the pencil to be in motion in the first case, but perceive the dot to be
stationary in the second case?
Because in one case there is an eye movement
We can create misperceptions of movements
Similar effects can be observes with saccadic eye movements
Saccades move (rotate fovea) to object of interest move as quickly as fossible to reduce travel
time during which vision is blurred
Yarbus(1967) scanpaths reveal intentions and interests
3-4 saccades per sec
Tested using a mirror glued to the side of the eye
If girl is speaking we fixate on the mouth and eyes
Scanpaths shift depending on our intentions
False motion and retinal smear during saccades
Why dont we notice that?
Spatial constancy: tricky problem of discriminating motion across the retina that is due to
eye movements vs. Object movements
Demonstate why?
Saccadic Suppression: reduction of visual sensitivity that occurs when one makes a saccadic
eye movements, eliminates smear from retinal image motion during an eye movement
Remaining questions:
When to suppress?
Insufficient: displacements across saccades should result in apparent motion illusions ( but
doesnt)
Compensation Theory: Perceptual system receives info about eye movement and discounts
changes in retinal image that result from it
Motor system sends motor command to eye muscles
www.notesolution.com
A copy of that command(efference copy) goes into an area of visual system that has been
dubbed `comparator``
Comparator compensates for image changes caused by the eye movement, inhibiting any
attempts by other parts of the visual system to interpret changes as object motion tapping
the side of your eye
Superior culiculus to central eye field, efference copies are sim signals that tell the brain
what the eye muscles are doing. Predicts that the eye muscle will contract. Human body
uses everywhere used when palm of hand and run ur fingers on that palm. Efferent copy
dismisses this activity when the sensory information is not important
When you know about the degree of the change you can ignore the information , comparator
sees two signals are exactly opposite
Limits of compensation theory
Perisaccadic misperceptions: briefly flashed stimuli appear as shifted in the direction of the
saccade, well before the saccade
Shift around time of saccade, might see compression of space, comp theory doesn`t work
perfectly
Euclidian Geometry: Parallel lines remain parallel as they are extended in space
Objects maintain the same size and shape as they move around in space
Which sense is governed by Euclidian geometryÉ
Problems for vision: recover 3D info from 2D projections
Most depth cues can be derived from geo consqeunces of the projection
2 retinal images of a 3D world are not the same ;; Parallax
Binocular disparity- the diffs between 2 retinal images of the same scene-it is the basis of
stereopsis, a vivid perception of the 3d of the world that is not available with monocular
vision.
Monocular vs binocular cues
Binocular cues provide convergence, stereopsis, ability of the two eyes to see more of an
object than one eye
Monocular Cues
www.notesolution.com

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Description
PERCEPTION LECTURE 6 eye movements- 6 muscles are attached to each eye and are arranged in three pairs InferiorSuperiorLateralMedial Rectus InferiorSuperior oblique Controlled by 3 cranial nerves Need to tell a person about up down.leftright back and forth 3 numbers are necessary for location Need numbers to describe orientation of object in space 3 numbers Controlled by extensive network of structures in the brain Superior Colliculus : structure in the midbrain that plays and important role in initating and guiding eye movements 2 muscles to rotate an object , 6 muscles in total Occulomotor nucleus gives rise to occulomotor nerve rect sup , medial rect, inf rect, inferior oblique Troclear innervates opposite side superior obliques Abducens innervates lateral rectus When stimulated with elec signals, eye movements are observed Layers involved in motor control, and visual Eye movements: Smooth Pursuit; eyes move smoothly to follow a moving object Saccade: Rapid movement of eyes that change fixation from one object or location to another Vergence Eye Movements: Type of eye movement in which two eyes move in opposite directions done deliberately Fixation eye movements, microsaccades Sometimes not possible to keep eyes fixated Eyes make counterrotations and need to correct for the rotation of the head Function of smooth pursuit eye movements,keep object of interest stable and on the fovea www.notesolution.com
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