6.2

Introduction to Sensation and Perception

• Sensation: The raw data collected by sensory organs.

• Perception: The brain's interpretation of sensory data, creating a model of reality.

• Importance: Understanding how these processes work helps us navigate and interact with our environment.

Visual System Overview

• Vision as a Primary Sense: Most dominant sense for humans, crucial for navigation, recognizing faces, and reading emotions.

• The Illusion of Vision: What we see is filtered through brain assumptions, shortcuts, and errors, creating a constructed reality rather than a perfect representation of the external world.

The Anatomy of the Eye

• Cornea: Protective layer that controls light entry.

• Aqueous Humor: Nourishing liquid in the front part of the eye.

• Iris & Pupil: Regulates light amount entering the eye, similar to a camera's aperture.

• Lens: Focuses light through accommodation, manipulated by the ciliary muscle.

• Vitreous Body: Gel-like substance in the eye.

• Retina: Light-sensitive layer where light is converted into electrical signals for the brain to process.

  • Photoreceptors:

    • Rods: Detect light/dark, optimized for low light but not color.

    • Cones: Detect color and fine details, needing bright light, concentrated in the fovea for sharp vision.

Blind Spot: Area on the retina without photoreceptors, filled in by the brain using surrounding information.

Color Perception

• Color as Interpretation: Exists as a perceptual experience, not in the environment as a fixed attribute.

• Trichromatic Theory: Three cone types (S cones for blue, M cones for green, L cones for red) combine to create color perception.

• Opponent Process Theory: Brain processes colors in opposing pairs (red-green, blue-yellow, black-white) and explains afterimages and color blindness.

• Color Blindness: Missing or malfunctioning cones can result in difficulties perceiving certain colors (e.g., red-green color blindness).

Depth Perception

• Monocular Cues: Allow depth perception with one eye (relative size, interposition, linear perspective, texture gradient).

• Binocular Cues: Use both eyes, such as retinal disparity (difference between images from both eyes) and convergence (inward turning of the eyes for close objects).

• Visual Illusions: Demonstrations of perception errors (e.g., forced perspective, Ames room).

Visual Processing in the Brain

• Visual Cortex: Located in the occipital lobe, where raw data transforms into a visual experience.

• Feature Detectors: Neurons respond to specific visual elements (lines, edges, contrast).

• Ventral Stream (What Pathway): Processes object and face recognition.

• Dorsal Stream (Where Pathway): Processes spatial awareness and movement.

• Conditions affecting visual perception:

  • Blindsight: Respond to visual stimuli without conscious awareness.

  • Motion Blindness: Difficulty perceiving moving objects, leading to fragmented visual experiences.

Final Thoughts on Vision

• The eye collects light that the brain interprets to construct a three-dimensional understanding of reality, emphasizing the complexity of perception.

• Guiding Principle: All models of reality are inherently flawed but can still be useful for navigating the world.

• Understanding perception helps reveal that seeing is not about passively receiving information but actively constructing meaning from data.