Lecture Notes: Visual Information Processing

Key Concepts

• Neurons transmit and integrate sensory information
• Focus on how visual information is processed

Sensory Reception

• Information from surroundings received through senses:
  • Vision: Eyes
  • Hearing: Ears
  • Smell/Taste: Nose/Mouth

Overview of Vision

• Light interacts with the eyes to create vision
• Light behaves as both a wave and a particle (photon)
• Visible light: Electromagnetic radiation with wavelength 400-700 nanometers
  • Our eyes evolved to perceive this range
  • Other species may perceive different ranges

Eye Structure and Function

• Pupil: Light enters the eye
• Iris: Regulates light amount (constriction/dilation)
• Lens: Focuses light onto the retina
• Retina: Contains photoreceptors (rods and cones)

Depth Perception

• Binocular disparity: Difference in image position on two retinas aids depth perception

Photoreceptors: Rods and Cones

• Rods:
  • Responsible for scotopic (dim light) vision
  • High sensitivity, low acuity (many rods converge onto one ganglion cell)
• Cones:
  • Responsible for photopic (bright light) vision
  • Low sensitivity, high acuity (few cones converge onto one ganglion cell)

Fovea

• Central region of the retina with only cones
• Specializes in high-acuity vision
• Rods increase in density moving away from the fovea

Sensitivity to Light Wavelengths

• Cones: Max sensitivity at ~560 nm (yellow light)
• Rods: Max sensitivity at ~500 nm (bluish-green light)
• Purkinje Effect: Changes in perceived brightness as lighting changes

Color Perception

• Trichromatic Color Theory: Three cone types (red, green, blue)
• Opponent Process Theory: Excitatory and inhibitory responses control color perception
  • Negative afterimages result from cone fatigue

Visual Transduction

• Rhodopsin: Pigment in rods; absorbs light and initiates signaling
  • Dark: Sodium channels open, rod is depolarized, releasing glutamate
  • Light: Rhodopsin bleaches, sodium channels close, rod hyperpolarizes, reducing glutamate release

Pathway to the Brain

• Action potentials from retinal ganglion cells travel via optic nerve to:
  • Lateral geniculate nuclei (thalamus)
  • Primary visual cortex (occipital lobe)

Visual Cortex Organization

• Parvocellular Layers (P): Respond to color and fine details
• Magnocellular Layers (M): Respond to motion
• Neurons organized in vertical columns corresponding to specific retinal areas

Brain Areas Involved

• Primary Visual Cortex: Receives input from lateral geniculate nuclei
• Secondary Visual Cortex: Input from primary visual cortex
• Visual Association Cortex: Input from secondary and other areas

Visual Processing Streams

• Dorsal Stream: Interprets spatial information (location/motion)
• Ventral Stream: Interprets object characteristics (color/shape)

Conclusion

• This lecture covered the mechanisms of visual information processing
• Future lectures will continue with further details on visual processing and other senses.