PSYC 330 Chapter Notes - Chapter 7: Visual Angle, Statistical Power, Medial Rectus Muscle
4 Jun 2018
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Department
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Professor
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CH7 Eye Movements
Will the absence of attention at the eye movement destination affect task performance?
What role does attention play in making eye movements?
Retinal organization & foveation
- Fovea: a small depression in the centre
of the retina that carries out highest
acuity visual processing
- Contains photoreceptors, cones
that enable finely detailed visual
input to be perceived clearly
- When looking at an object,
information about it is projected
to the fovea
- Outside fovea: contains rods - sensitive to movement, low-resolution visual analysis
- Trade off: greater acuity provided by foveal receptors (VS peripheral retinal receptors)
comes at the cost of decreased sensitivity to changes in light intensity and positions of
objects
- Foveal optic nerve fibres have small receptive fields → less photoreceptors
(high acuity) → less sensitive to light changes and motion
- Retinal organization is efficient
- high-acuity analysis of foveated stimuli
while remaining vigilant and sensitive to
stimulus events that may occur in the visual
periphery
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2
- Maintained by six oculomotor muscles that act as three antagonistic pairs
- One pair is responsible for side-to-side movements (SO & IO)
- One pair is responsible for up-and-down movements (SR & IR)
- One pair is responsible for rotational movements, inward and outward (lateral/
medial rectus)
- We make over 100,000 eye movements during the course of a day, oculomotor muscles
are resistant to fatigue
Visual angle of fovea & parafovea
- Some species have restricted eye movements
- Barn owls move their neck
- A women who couldn’t move her eyes, so when she reads, she makes the same
jump/ rest movements with her head
Types of EMs
Vestibular movements: keep looking at something but we turn our heads
Vergence movements: when eyes converge/ diverge, when looking at something close to you
Microsaccades: eyes are constantly jiggling/ drift, not consciously aware of them
- Eg after image of grid drifts and shakes - if you stare too long at a dot, the
grid around it kind of starts shaking too → b/c your eyes are moving, not the
thing
- Contact lens that has a picture on it, so when you move, it moves you (vision
fades to a gray mist)
Saccades & scanpaths
- Saccades: the most frequent one, rapid, ‘jump
and rest’ (discrete) foveations of objects
- Stimulus-driven saccade: initiated by
sensory events such as abrupt-onset
stimuli
- Goal-driven saccade: initiated on the
basis of the observer’s goals and
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3
intentions (make an eye movement to the symbolically cued location)
■ A series of fixation periods during which the eyes are relatively still while
visual analysis of the foveated object is carried out → ‘scan paths” →
trajectory of the next saccade is calibrated
- When triggered another saccade → eyes can be moved without further
programming (Ballistic eye movement)
- During programming, require precise information about their
destination → a slow saccade calibration process
- But once they are initiated, they are extremely rapid and require
no additional feedback to be guided to destinations
■ Superior colliculus plays a role in
saccade programming
- Active before and during
saccades and attention
shifts
- Topographically organized
cells in its upper layers,
while not very sensitive to
shape/ color, are quite
sensitive to visual
movement and location
Smooth pursuit movements
- A smooth, slow motion without abrupt starts and stops
■ (analog attention, processing focus is ‘turned on’ to track moving objects)
■ Eyes move in correspondence with moving objects (when tracking)→
maintain foveation
- Match slowly moving objects almost perfectly, but we have a tendency to
under-pursue rapidly moving objects
- When under-pursuit occurs → position of the objects image on
the retina slips out of the foveal region rather than remaining in
a constant position → objects are blurry and smeared
- Accuracy improves with practice and is learned
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Document Summary
Fovea: a small depression in the centre of the retina that carries out highest acuity visual processing. Contains photoreceptors, cones that enable finely detailed visual input to be perceived clearly. When looking at an object, information about it is projected to the fovea. Outside fovea: contains rods - sensitive to movement, low-resolution visual analysis. Trade off: greater acuity provided by foveal receptors (vs peripheral retinal receptors) comes at the cost of decreased sensitivity to changes in light intensity and positions of objects. Foveal optic nerve fibres have small receptive fields less photoreceptors (high acuity) less sensitive to light changes and motion. High-acuity analysis of foveated stimuli while remaining vigilant and sensitive to stimulus events that may occur in the visual periphery. Maintained by six oculomotor muscles that act as three antagonistic pairs. One pair is responsible for side-to-side movements (so & io) One pair is responsible for up-and-down movements (sr & ir)
