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

The Visual System

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

Vision = Perception of Light

• Light– Particles– Waves

• To humans, light = waves between 380-760 nanometers long

• Other wavelengths are visible to other animals

Figure 6.9 The electromagnetic spectrumKlein/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 retinaKlein/Thorne: Biological Psychology© 2007 by Worth Publishers

The Retina

Figure 6.4 The convergence of rods and cones onto ganglion cellsKlein/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 eyeKlein/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

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-HelmholtzTrichromatic Theory

• Three different types of color receptors• Each type is sensitive to different color

– Red– Green– Blue or violet– Fig. 6.26

Young-HelmholtzTrichromatic 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)