Biopsychology Notes - Chapter 6

Page 1

Intro to Chapter w/ some definitions (137-138)

Page 2

The Stimulus (138)

KEY CONCEPTS

Light, a form of electromagnetic radiation, can vary in wavelength, intensity, and purity; it can thus give rise to differences in perceptions of hue, brightness, and saturation.

Page 3

Anatomy of the Visual System (139-143)

The Eyes

Photoreceptors

Connections Between Eye and Brain

THOUGHT QUESTIONS

People who try to see faint, distinct lights at night are often advised to look just to the side of the location where they expect to see the lights. Can you explain the reason for this advice?

KEY CONCEPTS

The eyes are complex sensory organs that focus an image of the environment on the retina. The retina consists of three layers: the photoreceptor layer (rods and cones), the bipolar cell layer, and the ganglion cell layer.

Information from the eye is sent to the parvocellular, koniocellular, and magnocellular layers of the dorsal lateral geniculate nucleus and then to the primary visual cortex (striate cortex).

Page 4

Coding of Visual Information in the Retina (143-146)

Coding of Light and Dark

Coding of Color

THOUGHT QUESTIONS

Why is color vision useful? Birds, some fish, and some primates have full, three-cone color vision. Considering our own species, what other benefits (besides the ability to recognize ripe fruit, which I mentioned earlier in this section) might come from the evolution of color vision?

KEY CONCEPTS

When light strikes a molecule of photopigment in a photoreceptor, the molecule splits and initiates a receptor potential.

Ganglion cells of the retina respond in an opposing center/ surround fashion.

Colors are detected by three types of cones, and the code is changed into an opponent-process system by the time it reaches the retinal ganglion cells.

Page 5

Analysis of Visual Information: Role of the Striate Cortex (146-150)

Anatomy of the Striate Cortex

Orientation and Movement

Spatial Frequency

Retinal Disparity

Color

Modular Organization of the Striate Cortex

THOUGHT QUESTIONS

Look at the scene in front of you and try to imagine how its features are encoded by neurons in your striate cortex. Try to picture how the objects you see can be specified by an analysis of orientation, spatial frequency, and color.

KEY CONCEPTS

Neurons in the striate cortex are organized in modules, each containing two blobs. Neurons within the blobs respond to color; those outside the blobs respond to orientation, movement, spatial frequency, and retinal disparity.

Visual information is processed by two parallel systems: the magnocellular system and the parvocellular/koniocellular system.

Page 6

Analysis of Visual Information: Role of the Visual Association Cortex (150-161)

Two Streams of Visual Analysis

Perception of Color

Perception of Form

Perception of Movement

Perception of Spatial Location

THOUGHT QUESTIONS

Some psychologists are interested in “top-down” processes in visual perception—that is, the effects of context on perceiving ambiguous stimuli. For example, if you are in a dimly lighted kitchen and see a shape that could be either a loaf of bread or a country mailbox, you will be more likely to perceive the object as a loaf of bread. Where in the brain might contextual information affect perception?

I recently rented a car and soon discovered that one of the digital displays on the dashboard consisted of bright blue numbers against a black background. I found it difficult to clearly distinguish the numbers even though the blue color was really quite bright. The other digital displays were yellow, and I had no trouble recognizing the numbers they presented. Based on what you have learned in this chapter, can you offer a possible explanation for this phenomenon? (Hint: See the last paragraph in “Two Streams of Visual Analysis.”)

KEY CONCEPTS

Specific regions of the extrastriate cortex receive information about specific features of the visual scene from the striate ortex, analyze it, and send their information on to higher levels of the visual association cortex.

The association cortex of the inferior temporal lobe (ventral stream) recognizes the shape of objects, whereas the parietal cortex (dorsal stream) recognizes their location.

Damage to the visual association cortex can disrupt visual perception. The fusiform gyrus on the base of the occipital lobe is involved in the perception of faces. An adjacent region is involved in the perception of bodies and body parts, and the parahippocampal gyrus contains a region involved in the perception of environmental scenes. A region located in the extrastriate cortex (V8) is involved in color vision.

The region corresponding to area V5 is involved in the perception of movement, and a nearby region (MSTd) is involved in the perception of optic flow. Five regions within the intraparietal sulcus are involved in visual attention; control of eye movements; visual control of reaching, pointing, grasping, and manipulating; and perception of depth from stereopsis.

Page 7

Locations and Response Characteristics of Photoreceptors

Page 8

Properties of the Magnocellular, Parvocellular, and Koniocellular Divisions of the Visual System

Page 9

Regions of the Human Visual Cortex and Their Functions

Page 10

Resources