The Visual System

Figure 6.1 A cross-sectional view of the human eye Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

Vision = Perception of Light Light –Particles –Waves To humans, light = waves between nanometers long Other wavelengths are visible to other animals

Figure 6.9 The electromagnetic spectrum Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

The Visual System Retina –Photoreceptors Rods Cones –Bipolar cells –Ganglion cells

Figure 6.3 Cellular organization of the retina Klein/Thorne: Biological Psychology © 2007 by Worth Publishers The Retina

Figure 6.4 The convergence of rods and cones onto ganglion cells Klein/Thorne: Biological Psychology © 2007 by Worth Publishers Rods and Cones

Cones and Rods RODS Helps you see in the dark (more sensitive to light) Not good for seeing color Not good for seeing details CONES Most active when there is a lot of light Helps you see color Helps you see fine details

Figure 6.1 A cross-sectional view of the human eye Klein/Thorne: Biological Psychology © 2007 by Worth Publishers Fovea: Super sharp vision

Blind spot Visual system takes the info from the rest of the retina, and fills in the blank.

From the eye to the brain

Fig. 6.6 Fig. 6.8

Primary Visual Cortex Also known as the striate cortex First stage of processing for visual information

Secondary Visual Cortex Transmits information to other areas of brain

Blindsight Damage to occipital lobe Person is able to respond to an object even though not consciously aware of seeing it Most often associated with object that is moving

The Case of D.B. Right occipital lobe removed Things that are in left visual field are never perceived Therefore, D.B. had no awareness of seeing things in left visual field But… –Could reach for things in left visual field –Could differentiate vertical line from horizontal or diagonal line –Could differentiate letters “X” and “O”

Dorsal stream Where –Reach accurately for object Ventral stream What –Describe the object

Alternative explanation Dorsal stream Where Control of behavior Ventral stream What Conscious perception

Visual Agnosia Cannot name an object they see But can identify object if presented in a different mode (e.g., touch) Can see features of object but cannot integrate

Visual Prosopagnosia The inability to recognize faces

Depth Perception

Monocular depth cues –Able to gauge depth using only one eye

Monocular depth cues: Fig 6.23

Depth Perception Binocular depth cues –Retinal disparity

Color Perception

Young-Helmholtz Trichromatic Theory Three different types of color receptors Each type is sensitive to different color –Red –Green –Blue or violet –Fig. 6.26

Young-Helmholtz Trichromatic Theory The color that you see is the result of a mixture of activity of each type of color receptor E.g., yellow = activation of green and red fibers Research suggests that there are in foact three types of cones

Hering’s Opponent Process Theory Perception of color is based on pairs of complementary colors Red-Green, Yellow-Blue, Black-White For example: cells signal the color red by being hyperpolarized, and signal green by being depolarized

Hering’s Opponent Process Theory Perception of color is based on pairs of complementary colors Red-Green, Yellow-Blue, Black-White For example: cells signal the color red by being hyperpolarized, and signal green by being depolarized

Opponent Process Theory Negative afterimage Fig. 6.25

Opponent Process Theory Research has also found support for opponent process theory: –E.g., there are cells that are activated by red and inhibited by green, and vice ersa

Opponent Process Theory May account for color defects, which occurs in pairs (e.g., blue-yellow)