Lecture on the Visual System

Introduction

• Importance of understanding the visual system from a cognitive ergonomics perspective.
• Distinction between sensation, perception, and attention.

Key Concepts

Sensation

• Process of detecting and encoding stimulus energy in the world.
• Involves detecting visual and auditory information.

Perception

• Organizing and interpreting sensory information to give it meaning.
• Example: Organizing shapes to perceive a face.

Attention

• Selecting objects or events for conscious analysis.
• Acts as a filter for sensory information, focusing on what is important.

The Visual System

• Complex system, discussed here in a high-level overview.
• Visual stimulus enters through the eye, processed by retina, optic nerve, and finally the primary visual cortex.

Human Color Spectrum

• Visible range: 400 to 700 nanometers.
• Ultraviolet and infrared spectrums are not visible to humans.
• Other species have different ranges.
  • Example: Bees see beyond human range into ultraviolet.

Retina and Photoreceptors

• Retina: First processing stage for visual information.
  • Contains photoreceptors.
  • Two main areas: Fovea (central) and Periphery.

Types of Photoreceptors

• Cones

  • More prevalent in the fovea.
  • Sensitive to light, colors, and movements.
  • High sensitivity to color in the center of the visual field.

• Rods

  • Common in the periphery.
  • Used for night vision, less sensitive to color changes.

Visual Processing

• Convergence
  • Cones have low convergence (1:1 ratio with neurons).
  • Rods have high convergence (many-to-one ratio).
  • Low convergence leads to better visual acuity for cones.

Color Vision

• Trichromatic Theory: Three types of cones (Short, Medium, Long).
  • Short: Sensitive to blue.
  • Medium: Sensitive to green.
  • Long: Sensitive to red.

Color Vision Deficiency

• Monochromacy: Absence of two or three types of cones.
• Dichromacy: Only two types of cones function properly.

Visual Information Processing

• Visual information goes through neural populations (bipolar and ganglion cells).
• Optic Chiasm: Information relayed to different brain hemispheres.

Pathways in Visual Cortex

• Ventral (WHAT) Path: Processes color, texture, shape, size.
• Dorsal (WHERE) Path: Processes spatial information, location, movements.

Clinical Implications

• Damage to the WHERE path can result in spatial processing issues (e.g., dyslexia).
• Damage to the WHAT path affects object identification.

Conclusion

• Overview of the visual system covered.
• Important topics: retina, photoreceptors, and visual pathways.
• Next lecture: Focus on perception and brain organization of sensory information.