PSYC213_Lecture5.docx - PSYC213 u2013 Lecture 5 u2013...

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
o 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
o Step 4: This signal exits through the optic nerve to be sent to the brain
 Functional specialization
 Retinotopic map in the primary visual cortex
o Visual Association Area: Interprets information acquired through the primary visual cortex
o Primary Visual Cortex: Size, color, light, motion, dimensions
 Two pathways form the visual cortex
o What (ventral) pathway
 Object recognition
o Where (dorsal) pathway
 Spatial location
 If damaged, motion perception is impaired
 Akinetopsia
o 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
o An inability to recognize faces while still being able to recognize other visual objects
o Damage to fusiform face area
o Different forms
 Problem perceiving faces
 Faces look contorted
 Problem attaching meaning to faces
 Faces cannot be identified
o Different causes
 Acquired (brain injury)
 Congenital (genetic)
 Apperceptive visual agnosia
o A failure to recognize objects because of problems perceiving the object
o 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

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