The Visual System Flashcards
Lens
clear structure that focuses light onto back of eye
Accommodation
lens can change shape to focus light
Retina
lines inner surface, consists of specialized receptors that absorb light and send signals to brain
Photoreceptors
Specialized receptors at back of retina
Made of rods and cones
Ganglion Cells
Gather info from photoreceptors, fires signal
Optic Nerve
dense bundle of fibres that connect to brain, signal from ganglion cells sent out of eye through here
Optic Disc
area on back of retina with no photoreceptor, creates blind spot
Trichromatic Theory-/ Young- Helmholtz Theory
colour vision is determined by three different cone types that are sensitive to short medium and long wavelength of light
Opponent Process Theory
we perceive colour in terms of opposing pairs (red/green, yellow/blue, white/black)
-See red, then when red is no longer being seen, green (which was inhibited before) is free to fire
Rods
occupy peripheral regions of retina, highly sensitive under low light levels, very sensitive to black and gray
10-1 ratio between rods and ganglion cells
Cones
sensitive to different wavelengths of light (colours), clustered around fovea (central region of retina)
1-1 ratio between cones and ganglion
Dark Adaptation
rods and cones become increasingly sensitive to light under low levels of illumination
Colour Blindness
Proteins in cones sensitive to red and green, colourblind people have green cones that contain red cone protein instead
Nearsightedness/Myopia
Elongation of eyeball, causing image to fall short of retina
Farsightedness/Hyperopia
Image focused behind Retina
Optic Chiasm
Point at which optic nerves cross at midline of brain
Lateral Geniculate Nucleus
Sends message to visual cortex
Feature Detection Cells
cells in visual cortex that respond selectively to simple and specific aspects of a stimulus, such as angles and edges
Ventral Stream
Part of secondary visual cortex
- From visual cortex to lower part of temporal lobe
- Responsible for object recognition, and names object
Dorsal Stream
Part of secondary visual cortex
- From visual cortex to parietal lobe
- Locates object in space, allows you to interact with it
Perceptual Constancy
ability to perceive objects as having constant shape, size, and colour despite changes in perspective
Binocular Dept Cues
Distance cues based on differing perspectives of both eyes
Binocular Dept Cues: Convergence
eye muscles contract so that both eyes focus on a single object
Binocular Dept Cues: Retina Disparity/ Binocular Disparity
difference in relative position of an object as seen by both eyes- provides brain information about depth
Binocular Dept Cues: Stereoscopic Vision
overlapping visual fields
Monocular Cues
Dept cues perceived with one eye
Monocular Cues: Motion Parallax
Provides info about depth based on how quickly stationary objects appear to move
Thalamocortical Pathways
-Connetcs eyes to thalamus to cortex
Each stage builds on processing in previous stage
Eyes-> Thalamus-> Cortex
Cortical Blindness
Damage to cortex
Loss of conscious vision
Parts of Secondary Visual Cortex
Dorsal Stream
Ventral Stream
Dorsal Stream
goes upwards towards top of brain
-In charge of locating and interacting with objects
Ventral Stream
goes downwards towards bottom of brain
-identifies objects
