Optical Illusions and Human Vision

Introduction to Optical Illusions

• Optical illusions exploit the disconnect between sensation and perception.
• Types:
  • Illusions using light or perspective patterns.
  • Illusions producing ghost effects or afterimages.

Afterimage Illusion Example

• Flag Illusion: Stare at a colored flag and then a white screen to see an afterimage in different colors.
• Purpose: Illustrate the complexity of human vision.

Complexity of Human Vision

• 70% of sensory receptors in the body are in the eyes.
• Nearly half of the cerebral cortex is involved in vision.

Basics of Light and Vision

• Light as electromagnetic radiation traveling in waves.
• Hue: Determined by frequency of light waves.
• Brightness: Determined by amplitude of light waves.
• Visible light is a small part of the electromagnetic spectrum.

Photoreceptors and Light Conversion

• Photoreceptors convert light energy into nerve impulses.
• Eye Anatomy:
  • Outer Accessories: Eyebrows, eyelashes for protection.
  • Eyeball Structure: 2.5 cm in diameter, mostly hollow.
  • Layers of the Eye:
    • Fibrous Layer: Includes sclera and cornea.
    • Vascular Layer: Contains choroid, ciliary body, iris.
    • Inner Layer: Retina with photoreceptor cells.

Vision Process

• Light enters through cornea and pupil to the lens.
• Focused light hits the retina, where photoreceptors convert it to electrical signals.
• Pathway: Photoreceptors → Bipolar neurons → Ganglion neurons → Optic nerve → Thalamus → Visual cortex.

Photoreceptors: Rods and Cones

• Cones:
  • Located near retina's center.
  • Detect fine detail and color.
  • Types: Red, green, blue-sensitive.
  • Work best in bright conditions.
• Rods:
  • More numerous and light-sensitive.
  • Detect grayscale, operate in peripheral vision.
• Wiring:
  • Rods: Multiple rods share a ganglion cell.
  • Cones: Individual cones have their own ganglion cells.

Explanation of Flag Illusion

• Afterimages: Result from overstimulated photoreceptors continuing to fire.
• Cone Fatigue: Prolonged stimulus causes cones to stop responding.
• When looking at a white space after the flag:
  • Cones: Only red cones respond, changing perceived colors.
  • Rods: Register a negative image effect, altering light and dark perception.

Conclusion

• Human vision is complex but fallible.
• Understanding vision helps learn about anatomical and physiological aspects of the eye.
• Thanks to contributors and supporters of educational content creation.