Psych 261 Chapter 6 Psych 261 Physiological Psychology Kalat: Biological Psychology 10th Edition Chapter 6

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Published on 16 Oct 2011
School
University of Waterloo
Department
Psychology
Course
PSYCH261
Psych 261 Chapter 6: Vision
Module 6.1
Visual Coding
-light rays bounce off objects in all directions; only see rays that hit retina perpendicularly
General Principles of Perception
-perceive objects by energy they transmit (eg. reflect light); store and encode info. In terms of neuron response
-law of specific nerve energies: 1 aspect of coding = which neuron is active; impulses in some neurons indicate
light
-light stimulates specific set of receptors; stimulus strength, coding, etc. depends on firing rate
From Neuronal Activity to Perception
-Brain activity does not duplicate the object you see
The Eye and its Connections to the Brain
-light enters via pupil; focused by lens and cornea; projected to retina (lined w/ visual receptors); light strikes
contralaterally
Route within the Retina
-message goes from retina (back) to bipolar cells (center) to ganglion cells (center) then to brain
-ganglion cells form optic nerve at back of eye; point where light leaves forms blind-spot (no light receptors)
Fovea and Periphery of the Retina
-fovea: central portion of retina; specialized for acute, unimpeded, detailed vision; hawks have 2 foveas
-midget ganglion cell: G cell in fvea; small, responds to single cone; peripheral vision: better sensitivity to dim
light
Visual Receptors: Rods and Cones
-2 receptors: rods: by periphery, good at faint light; Cones: near fovea: colour vision and bright light
-rods/cones ratio is 20/1: cones: 90% of brain input; rods share ganglion cells, line w/ others
-photopigments: chemicals: release energy where struck by light
Color Vision
-wavelength: determines colour; eg purple=short, red=long
Trichromatic (Young-Helmholtz) theory
-found: perceive color via relative rate of response by 3 kinds of cones (each cone sensitive to diff. wavelength
-short, medium, and long wavelength type cones; ratio of response of a wavelength to 3 determines color
-long/med cones more abundant than short; thus harder to see blue than red/yellow
The opponent process theory
-negative color after-image: image seen after staring @ bright light; colours switch
-opponent-process theory: perceive colour in terms of opposite; eg. continuums of red-green, yellow-blue
-after images depend on whole context: not just the light on individual receptors
The Retinex theory
-color constancy: ability to recognize color despite change in lighting
-perception of color depends on comparing w/ other colours, same w/ brightness
-retinex theory: cortex compares info from retina to determine brightness & colour
-hence: requires reasoning
Color Vision Deficiency
-aka color blindness; lack one-two types of cones, have an abnormal cone
-trouble (usually) from distinguishing red & green as photopigments are same in both
-usually more for males than females as gene deficiency is in X chromosome
Module 6.2
Neural Basis of visual perception
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Document Summary

Light rays bounce off objects in all directions; only see rays that hit retina perpendicularly. Perceive objects by energy they transmit (eg. reflect light); store and encode info. Law of specific nerve energies: 1 aspect of coding = which neuron is active; impulses in some neurons indicate light. Light stimulates specific set of receptors; stimulus strength, coding, etc. depends on firing rate. Brain activity does not duplicate the object you see. The eye and its connections to the brain. Light enters via pupil; focused by lens and cornea; projected to retina (lined w/ visual receptors); light strikes contralaterally. Message goes from retina (back) to bipolar cells (center) to ganglion cells (center) then to brain. Ganglion cells form optic nerve at back of eye; point where light leaves forms blind-spot (no light receptors) Fovea: central portion of retina; specialized for acute, unimpeded, detailed vision; hawks have 2 foveas.

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