Chapter_6

Chapter Overview

• Title: Vision

• Authors: Neil R. Carlson, Melissa A. Birkett

• Content Overview: This chapter covers the principles of vision, including how light interacts with the eye, visual pathways, and the perception of color, form, distance, orientation, and movement.

Page 1

• Text: 13th EDITION

• Highlight: Introduction to the chapter focusing on Vision.

Page 2-3

• Topics Covered:

  • Light

  • The Eye

  • Visual Pathways

  • Perceiving Color

  • Perceiving Form

  • Perceiving Distance

  • Perceiving Orientation and Movement

Light (Page 4)

• Visible Light: A narrow band of the electromagnetic spectrum crucial for vision.

• Three Dimensions of Light Important for Vision:

  • Hue: Wavelength of light

  • Brightness: Intensity of light

  • Saturation: Relative purity of light

The Eye (Page 6)

• Definitions:

  • Sensation: Detecting external stimuli

  • Perception: Organizing and interpreting sensations

  • Transduction: Converting external stimuli (energy) into neural signals

• Photoreceptors: Specialized neurons converting light into neural signals.

Anatomy of the Eye (Page 7-10)

• Components:

  • Sclera: The white outer coat of the eyeball

  • Cornea: Transparent layer that bends light

  • Iris: Colored muscle controlling pupil size

  • Pupil: Opening that allows light into the eye

  • Lens: Focuses light on the retina

  • Vitreous Humor: The clear gel filling the eye

  • Retina: Contains photoreceptors and layers including Fovea (high acuity) and Optic Disk (blind spot)

• Extraocular Muscles: Control eye movement.

Layers of the Retina (Page 11-12)

• Retina Structure:

  • Photoreceptor Layer: Contains rods and cones

  • Bipolar Cell Layer: Connects photoreceptors to ganglion cells

  • Ganglion Cell Layer: Outputs visual information from the eye

Rods and Cones (Page 13-14)

• Types of Photoreceptors:

  • Cones:

    • Found mainly in the fovea (6 million)

    • Responsible for color vision and high acuity

    • Require bright light

  • Rods:

    • Found in the peripheral retina (120 million)

    • Responsible for night vision and motion detection

    • Sensitive to low light levels

Bipolar Cells Interaction (Page 15-16)

• ON and OFF Bipolar Cells:

  • Photoreceptors hyperpolarize in response to light, leading to less glutamate

  • ON Bipolar Cells depolarize and release more glutamate to ganglion cells

  • OFF Bipolar Cells are inhibited by light and decrease glutamate release.

Receptive Fields (Page 20-24)

• Definition: Area in the visual field a cell responds to.

• Center and Surround Effects:

  • Opposite effects on ganglion cell responses based on stimulation

  • ON and OFF ganglion cells respond based on light in different areas of the receptive field.

Visual Pathways (Page 26-33)

• Pathway Overview:

  • Axons from ganglion cells form optic nerves

  • Visual information crosses at the optic chiasm

  • Projects to the lateral geniculate nucleus (LGN), then to the primary visual cortex

  • Two streams: Dorsal (where) and Ventral (what).

Perceiving Color (Page 35-41)

• Color Vision:

  • Three types of cones respond to red, green, and blue light

  • Color blindness results from deficiencies in photopigments

  • Ganglion cells process color using an opponent-color system

  • Striate cortex (V1) analyzes inputs from LGN regarding color.

Perceiving Form (Page 43-48)

• Recognition Areas:

  • Inferior temporal cortex recognizes patterns, including faces and body parts

  • Damage results in visual agnosia, preventing object recognition despite preserved visual acuity

Perceiving Distance (Page 50-52)

• Depth Perception:

  • Monocular and binocular cues help perceive distance

  • Important for movement accuracy and navigation.

Perceiving Orientation and Movement (Page 54-56)

• Striate Cortex: Neurons responsive to orientation of lines

• Extrastriate Cortex (Area V5): Involved in motion detection; damage results in akinetopsia.