Understanding Human Vision and Optical Illusions

Optical Illusions and Vision

• Optical illusions exploit the disconnect between sensation (what the eyes see) and perception (what the brain understands).
• Some illusions create ghost effects or afterimages, utilizing glitches in human vision physiology.
• Example: Viewing a specially colored flag can produce an afterimage in different colors on a blank screen.

Human Vision Complexity

• Nearly 70% of the body's sensory receptors are in the eyes.
• Vision involves nearly half of the cerebral cortex.
• Vision is the dominant sense for humans.

Basics of Light

• Light is electromagnetic radiation traveling in waves.
• Frequency determines hue; amplitude determines brightness.
• Visible light is a small part of the electromagnetic spectrum.
• Photoreceptors convert light into nerve impulses.

Eye Anatomy

• Outer Accessories:
  • Eyebrows, eyelashes, eyelids, lacrimal apparatus help protect the eyes.
• Eyeball Structure:
  • Irregularly spherical, filled with fluid, mostly invisible inside the skull.
  • Walls composed of three layers: fibrous, vascular, inner layers.

Fibrous Layer

• Sclera: The white part of the eye.
• Cornea: Transparent window for light entry, sensitive to damage.

Vascular Layer

• Choroid: Provides blood supply to the eye.
• Ciliary Body: Muscle tissue surrounding the lens.
• Iris: Colored part, controls pupil size through sphincter muscles.

Inner Layer

• Retina: Contains photoreceptors for light conversion to electrical signals.
• Two layers: outer pigmented and inner neural.
• Photoreceptors:
  • Rods: Detect light/dark, more numerous, around retina edges.
  • Cones: Detect color, detail, concentrated in the center.

Rods vs. Cones

• Rods connect to one ganglion cell collectively; good for general shapes/light.
• Cones each connect to a separate ganglion cell; good for detailed color vision.

Afterimage Explanation

• After prolonged exposure to a color, cones can tire and stop responding.
• After switching to a white surface, only the non-fatigued cones respond, creating an afterimage.
• Rods contribute to afterimages as well, displaying a negative-like effect.

Conclusion

• Human vision, while fallible, is a complex system illustrating the anatomy and physiology of vision.
• Key structures: eye layers, retina components, rods and cones.
• Understanding illusions helps in grasping the visual system's complexity.