PSYA01H3 Chapter Notes - Chapter 6: Two-Streams Hypothesis

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Published on 28 Apr 2011
School
UTSC
Department
Psychology
Course
PSYA01H3
Chapter 6- Perception
Limitations of perception: we can hear and smell things but we cannot locate where it is
oOur perspective is limited to what we think and it the only one we have
oIf we could see P.O.V from another person
Vision received the most attention from psychologist b/c most important to humans
Perception: process which we recognize what is represented by the information provided by
our sense organs gives unity and coherence to this input
oRapid, automatic, unconscious process
Example: we dont just see the cylinder, then the glass cup; we just perceive it as the glass.
Distinction btw sensation and perception is hard to distinguish
Brain Mechanisms of Visual Perception
Visual perception= hierarchy of information processing
* info that is sent from the eyes to the thalamus is then sent to the primary visual cortex, located in the
middle of the occipital lobes, back of the brain
THE PRIMARY VISUAL CORTEX
Research in the thalamus and primary visual cortex lead to knowledge of visual analysis
HUBLE & WEISEL: insert microelectrodes (small wires) in cats and monkeys; it detects axn
potentials in certain areas of the brain to see which gave most response.
Conclusion: geography of visual field is retained in the primary visual cortex like a map
Module: block of tissue approx 0.5x 0.7mm each w/ 150 000 neuron that receive info from the
same group of receptor cells in retina = about 2500 modules in primary visual cortex
oBunch of tiles working with one another processing the same information
Receptive field: part of visual field which what we see (visual stimuli) will produce
different firing rates of a particular neuron
oExample: some circuits detect presence of lines pass through based on the angle of
the line
oOthers detect mvment of lines and direction of mvments
oOthers detect lines colours
Neurons respond most when line is at 50 degrees
The different degrees that images are on the retina;
Respond less at 70 or 30 degrees when the line is passing through receptive field
Info from primary is sent to 2 levels parietal (visual association cortex) and temporal area
(2nd level of association in the cortex)
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The information from the optic kiasmic splits into different tracks to diff hemispheres of the
brain
left visual field projects to the right half of each retina is sent to the left hemisphere
right visual field projects to the left half of the retina is sent to the right hemisphere
info that is detected from the left half of the retina coming from right visual field is sent to
the left hemisphere
-then info from here is sent to the thalamus where the lateral geneculit nucleus; located one
on the right and one on the left
THE VISUAL ASSOCIATION CORTEX
Perception of objects and the total visual scene does NOT take place in PRIMARY
VISUAL CORTEX
Perception of objects and entire visual scenes must be combined; Visual Association
cortex + Primary visual cortex
Neurons in primary visual send axons to visual association
Visual association has 2 PATHWAYS
oVentral stream
oDorsal stream
Ventral stream (aka the P channel)- temporal lobe
Continue forward and end in inferior temporal cortex
FUNCTION: recognition of what an object is; the form it has, what colour and depth
Damage to visual association, occipital, and temporal lobe in ventral stream = visual
agnosia;
oVisual agnosia: (failure to know)in ability to perceive or identify a stimulus that
exists within a specific sensory modality
oExample: you dont recognize the clock, but only when you touch it you know its a
watch, not a circular image OR you dont recognize someones face, but when your
hear their voice or touch them, then you know who it is
Symptom of visual agnosia
oProsopagnosis: inability to recognize particular faces (prosopon= face)
Caused by damage to visual association
oPpl know they are looking at a face, but cant identify whose face it is
Not just limited to not recognizing faces, but also your own car; must read
license plate
FFA- fusiform face area- contain face recognizing circuits; region of the ventral stream located
base of the brain
oFFA is activated when experts of either cars or birds saw other cars and birds VS ppl
who arent experts at cars
oTarr and Gautheir renamed FFA to flexible fusiform area b/c of participation in
visual recognition of diverse objects
oExample: Autistic ppl, FFA is NOT activated = they have trouble identifying faces
and fail to realize ppl are around
Extrastriate body area (EBA)- region of occipital cortex next t primary visual cortex that
responds to forms resembling the human body (body parts, fake bodies, NOT drawings or pics
of bodies etc)
oExample: ppl lose ability to recognize pictures of body parts, but they can identify
faces
Parahippocampal place area (PPA)- located below hippocampus ; part of ventral stream
that is activated by visual scenes and backgrounds
oExample: ability to identify natural and man-made scenes like beaches, forests,
deserts, cities, markets and rooms BUT cannot recognize the objects that go w/ these
scenes, like benches in the part
Ventral stream: Perception of colour
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Document Summary

* info that is sent from the eyes to the thalamus is then sent to the primary visual cortex, located in the middle of the occipital lobes, back of the brain. The different degrees that images are on the retina: respond less at 70 or 30 degrees when the line is passing through receptive field. Info from primary is sent to 2 levels parietal (visual association cortex) and temporal area (2nd level of association in the cortex) www. notesolution. com. Then info from here is sent to the thalamus where the lateral geneculit nucleus; located one on the right and one on the left. Perception of objects and the total visual scene does not take place in primary. Perception of objects and entire visual scenes must be combined; visual association. Neurons in primary visual send axons to visual association. Visual association has 2 pathways: ventral stream, dorsal stream.

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