PSYB57H3 Chapter Notes - Chapter 2: Lateral Geniculate Nucleus, Ganglion Cell, Optic Nerve

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19 Dec 2010

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PSYB57-10W-W02 -Perception
Explain what perception is and how it is guided by cognition (pp. 50-51).
Condillac (1715-1780) believes that if sensation doesnt exist, there would no mental life.
-Sensation + Perception = basics of cognition
-providing the brain an interpretation of the external world, as these stimuli are analyzed.
-existing knowledge guides these dynamic processes.
-sensory input does not contain enough information to explain our perception (cube)
-Searching helps to del with the excess of input (painting, dog)
-Selective attention - choose part of sensory input for further processing in the expense of other aspects
of that input. (painting, dog)
Identify the structures of the visual system, including the dorsal and ventral pathways (pp.
The Visual System
Visual scene forms an image on the retina, the layer of cells that respond to light, photoreceptors, and
nerve cells at the back of the eye.
-light is converted into electrochemical signals, transmitted to brain via optic nerves.
- optic nerve = a bundle of the long axon fibers of the ganglion cells in retina.
-axons make contact with the neurons of the lateral geniculate nucleus (LGN) in
the thalamus.
-axons in LGN then send signals up to the primary visual cortex.
-beyond the primary visual cortex, 2 main pathways can be identified.
1. Dorsal Pathway 2. Ventral Pathway.
-1. Dorsal Pathway reaches up to parietal lobe: process
information about the location of item and how item might be
acted on ! guiding movements
-2. Ventral Pathway reaches down to the temporal lobe: process
information that leads to recognition and identification of
Bottom-top process - what we see. Top - bottom process - what we interpret from what we see.
Explain how critical periods are related to perceptual development (pp. 56-57).
Biological Structure of brain + experience (modifies the structure) = our view or world.
Critical periods: early life periods during which the animal must develop particular responses.
-eg. chicken + blind fold + first 6 months
-what we take in from our environment from this period alters the development of our
Explain what bottom-up processing is and how the processing of visual features includes
spots and edges, colors and shapes, and movements and textures (pp. 57-65).
Bottom-up processing: what we take in from our environment through our visual system. Extract features
that would allow subsequent processes to figure out what is out there in the world.
Spots and Edges
Visual field: the portion of the world that is visible at the present moment.
Ganglion cells is connected to a collection of photoreceptors. Ganglion cells will only respond to light that
lands on those receptors.
Receptor field of cell: an area of the visual field which a stimulus will affect the activity of the cell.
Center-surround cells (see below) organization of ganglion cells is well designed to pick out edges in the
visual environment.
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