PSYA01H3 Chapter Notes - Chapter 6: Visual Cortex, David H. Hubel, Saccade

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Published on 30 Jan 2011
School
UTSC
Department
Psychology
Course
PSYA01H3
Chapter 6 - Perception
Perception ±A rapid, automatic, unconscious process by which we recognize what is represented
by the information provided by our sense organs.
Brain Mechanisms of Visual Perception:
-2 successive levels of visual association cortex
-1st level surrounds the primary visual cortex
-2nd level in middle of parietal lobe and lower part of temporal lobe.
The Primary Visual Cortex:
Hubel & Wiesel Æ Mapped visual cortex
-Placed microelectrodes on animal brains and presented them visual stimuli
-Microelectrodes are small wires with points that detect neuron activity
-:KDWZHVHHLVPDSSHGRXWRQRXUEUDLQLQWLOHVFDOOHGPRGXOHVRU³UHFHSWLYHILHOGV´
-Modules = 0.5mm*0.7mm, 150 000 neurons each
-2500 modules in the human brain.
-Neurons detected different things (i.e. Some detect horizontal lines, vertical lines, color, etc)
Receptive Field ±The portion of the visual field in which the presentation of visual stimuli will
produce an alteration in the firing rate of a particular neuron.
The Visual Association Cortex:
-Different areas of the visual association cortex deal with different levels of vision.
-From the neurons that detect different things -> send info to particular areas of the visual
association cortex to be analyzed.
Effects of Brain Damage On Visual Perception
-If the primary visual cortex is damaged, the person is blind in that area (remember how what we
see is mapped on the brain)
-No difficulty in perceiving
-Damage to visual association cortex damages perceptive ability.
Achromatopsia ±The inability to discriminate among different hues; caused by damage to the
visual association cortex.
-The brain is contralateral damage to one side affects the other side of body
Î Damage to the achromatopsia causes the person to see no color what so ever.
%DOLQV6\QGURPH±A syndrome caused by bilateral damage to the parieto-occipital region of
the brain; includes difficulty in perceiving the location of objects and reaching for them under
visual guidance.
-They can tell that an object has changed positions, but cannot detect movement.
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Good Continuation ±A Gestalt law of organization; given two or more interpretations of
elements that form an outline of a figure, the simples interpretation is preferred
Law of Closure ±A Gestalt law of organization; elements missing from the outline of a figure
are filled in by the visual system
Î People see this as a triangle inside a circle with another triangle.
Î BUT really! THERE IS NO TRIANGLE
Î World for example. It gives us fragments.
Law of Common Fate ± A Gestalt law of organization; elements that move together give rise to
the perception of a particular figure. (e.g. Predator, although he is camouflaged perfectly when
stationary, if he moves, the camouflage moves together in the shape of a body and is thus
perceived as a whole.)
Alais, Blake & Lee Æ Law of common fate applies to changes other than movement
-Common Tempo = A temporal variation in contrast (brightness) that causes groups to be seen as
being together.
Î Example: walking across the room, FEET, ARMS is common fate.
Î ME TYPING THESE NOTES IS COMMON MATE -
Perception of Form ± Summary
7KXVDQXPEHURIODZVKHOSXVWRSHUFHLYHIRUP«WKDWLV to figure out what the objects are, and
how to interpret them despite actual sensations.
Once again, these laws are:
The law of proximity
The law of similarity
The law of good continuation
The law of closure, and
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Document Summary

Perception a rapid, automatic, unconscious process by which we recognize what is represented by the information provided by our sense organs. 2nd level in middle of parietal lobe and lower part of temporal lobe. Placed microelectrodes on animal brains and presented them visual stimuli. Microelectrodes are small wires with points that detect neuron activity. Neurons detected different things (i. e. some detect horizontal lines, vertical lines, color, etc) Receptive field the portion of the visual field in which the presentation of visual stimuli will produce an alteration in the firing rate of a particular neuron. Different areas of the visual association cortex deal with different levels of vision. From the neurons that detect different things -> send info to particular areas of the visual association cortex to be analyzed. If the primary visual cortex is damaged, the person is blind in that area (remember how what we see is mapped on the brain) Damage to visual association cortex damages perceptive ability.