Vision: light passes through cornea, aqueous humor, pupil, lens, and vitreous humor before forming an image on retina
Eye Structure
- Retina: light-sensitive surface containing rods, cones, layers of bipolar cells and ganglion cells that capture and transduce visual information to the brain
- Photoreceptors: include rods and cones
- Rods: black, white, gray and movement; peripheral and dim-light vision; throughout the retina, none in the fovea.
- Cones (blue, green, and red): color and fine detail; bright-light conditions; concentrated at the fovea; none in the periphery
- Bipolar cells: second layer, transmit from rods and cones to ganglion cells
- Ganglion cells: third layer, converge to form the optic nerve
- Blind spot: creates an area with no vision on retina (where the optic nerve leaves the eye so there are no receptor cells)
- Optic nerve: nerve formed by ganglion cell axons; carries the neural impulses to the brain
Acuity: ability to detect fine details; sharpness of vision
Accommodation: process of focusing light rays of visual stimuli onto the retina by the lens (issues in this process cause nearsightedness or farsightedness)
Dark adaptation: increased visual sensitivity that gradually develops when it gets dark
Color Vision
- Color vision is explained by both the trichromatic theory and the opponent-process theory
- Trichromatic theory: cones are differentially sensitive to different wavelengths of light; each color you see results from a specific ratio of activation among the three types of receptors
- Opponent-process theory: opposing retinal processes for red–green, yellow–blue, white–black; some retinal cells are stimulated by one of a pair and inhibited by the other
- Afterimage: certain ganglion cells (red/green; blue/yellow; black/white) in the retina are activated while others are not (supports opponent-process theory)
- Color vision deficiency: dichromatism/monochromatism, resulting from cones or ganglion cells damage/issues
Feature detectors: specific neurons in the visual cortex respond only to specific features (e.g. lines of particular angles, the edge of a surface, etc.)
Parallel processing: simultaneous processing of stimulus elements (e.g. color, contours, etc.)
Brain Damage
- Brain area: in the occipital lobe
- Prosopagnosia: face blindness
- Blindsight: can respond to visual information without consciously seeing it