PSYC213 – Lecture 5 –
Visual perception: Context and Theories
Last Class
Sensation
: Energy from a physical stimulus in the environment that is picked up by sense organs
Perception
: Follow sensation. When the brain sensed information and translates it into something
meaningful
McGurk effect and the brain
o
Compared brain activity for people who experienced the McGurk effect and those people who
did not experience this effect
o
This left superior temporal sulcus is important for audiovisual integration during speech
perception
More active for people who experience the McGurk effect
Individual differences are seen in the brain!
Early visual system
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Step 1:
Light waves enter the eye and are focused onto the retina, a thin layer of tissue at
the back of the eye
o
Step 2:
Photoreceptors in the retina convert light to electrical activity
o
Step 3:
This electrical signal is sent to bipolar cells then ganglion cells
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Step 4:
This signal exits through the optic nerve to be sent to the brain
Functional specialization
Retinotopic map in the primary visual cortex
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Visual Association Area: Interprets information acquired through the primary visual cortex
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Primary Visual Cortex: Size, color, light, motion, dimensions
Two pathways form the visual cortex
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What (ventral) pathway
Object recognition
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Where (dorsal) pathway
Spatial location
If damaged, motion perception is impaired
Akinetopsia
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World is like a series of snapshots
o
“
When I’m looking at the car first, it seems far away. But then when I
want to cross the road, suddenly the car is very near.” Patient with
Akinetopsia
Visual Agnosia
o
Damage to the visual processing areas (the what pathway) of the brain that result in
selectrive problems regonizing objects
Basic sensory systems are intact
Supports a dissociation between being able to see visual features and
interpreting those visual features
The specific area of the brain that is damaged determines which types (or features) of
objects cannot be recognized
Supports high level functional specialization
Prosopagnosia
o
A form of visual agnosia
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An inability to recognize faces while still being able to recognize other visual objects
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Damage to fusiform face area
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Different forms
Problem perceiving faces
Faces look contorted
Problem attaching meaning to faces
Faces cannot be identified
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Different causes
Acquired (brain injury)
Congenital (genetic)
Apperceptive visual agnosia
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A failure to recognize objects because of problems perceiving the object
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This is not a deficit in sensory processing
These cases can detect visual features
o
This is a problem with grouping visual features into a meaningful perception
o
Evidence
These cases cannot copy a simple line drawing
