Chapter 6: Vision

Chapter 6 covers the topic of vision. The opening section introduces the topics of sensory processing and the anatomy of the primate visual system, including the anatomy of the eye, the photoreceptors within the retina, and the neural pathways that connect the retina to visual cortex. The second section of the vision chapter introduces the notion of receptive fields and describes the organization of the retinal receptive fields. The processing of color coding at the retina and the lateral geniculate is described. Negative afterimages are related to retinal ganglion cell activity. The third section of chapter 6 describes the role played by the striate cortex in processing of information related to orientation and movement, texture, and color. Spatial frequency analyses are discussed in relation to visual processing. The blindsight phenomenon is discussed as an example of how sensory processing can occur in the absence of conscious awareness. The final section of chapter 6 introduces the notion that visual processing may occur in two streams of analysis that involve the activity of multiple brain regions, some located within striate cortex and others situated within visual association cortex. The section covers the role of visual association cortex in the analysis of color, form, movement, and location.

After completing the chapter, each student should be able to:

• Describe the general process of sensory transduction
• Describe the characteristics of light and color
• Outline the anatomy of the eye
• Compare and contrast the two types of photoreceptors
• Explain how the organization of the eye generates a retinal blind spot.
• Outline the anatomy of the retina
• Explain how retinal cells transduce light
• Explain how light-induced receptor hyperpolarization results in action potentials at the retinal ganglion cells
• Describe the visual neural pathways from eye to cortex
• Explain the concept of receptive field
• Describe what is meant by ON, OFF, and ON/OFF ganglion cells in the retina
• Explain and contrast the color vision theories proposed by Young and by Hering.
• Differentiate the four types of photoreceptors found in primate retina
• Explain the three types of defects in color vision
• Explain how the neural coding of color shifts form the photoreceptor level to the level of the retinal ganglion cell.
• Explain the concept of negative afterimage
• Describe the anatomy of the striate cortex
• Explain the approach used by Hubel and Wiesel to study the physiology of perception
• Compare the receptive fields of a simple cortical cell vs. a complex cortical cell
• Define spatial frequency
• Explain how cortical neurons code for spatial frequency in the visual field
• Explain the concept of modular organization
• Describe the modular organization of the striate cortex
• Explain the functions carried out by units within the visual modules including
• Within the CO "blob"
• Outside the CO "blob"
• Explain ocular dominance
• Define blindsight
• Explain the two streams of analysis carried out from eye to visual cortex
• Compare and contrast the anatomy and physiology of the parvocellular and magnocellular systems
• Define extrastriate cortex
• Explain how the inferior temporal cortex may play a role in perception of form
• Describe the effects of damage to visual association cortex in humans including:
• Apperceptive visual agnosia
• Prosopagnosia
• Describe how neurons in extrastriate cortex respond to movement and location