Lecture 2 – Perception_2025_ForUpload

Lecture 2 - Perception

Overview

  • Sensation and Perception

  • Types of Processing: Bottom-up and Top-down Processing

  • Object and Face Perception

Sensation vs. Perception

  • Sensation: Detection of external stimuli; occurs at sensory organs.

  • Perception: Interpretation and organization of sensory input by the brain.

Sensory Modalities & Their Pathways

  • Vision: Light waves ➔ Eye (retina) ➔ Optic nerve

  • Hearing: Sound waves ➔ Ear (inner ear) ➔ Auditory nerve

  • Taste: Molecules ➔ Tongue ➔ Facial, glossopharyngeal & vagus nerves

  • Smell: Molecules ➔ Nose ➔ Olfactory nerve

  • Touch: Pressure ➔ Skin ➔ Cranial and spinal nerves

From Sensation to Perception

  1. Stimulus: External stimulus detected.

  2. Sensation: Sensory receptors detect stimulus.

  3. Sensory Coding: Conversion of stimuli into neural signals.

  4. Perception: Brain interprets signals as meaningful experiences.

Qualitative and Quantitative Information

  • Qualitative: Basic qualities of stimuli (different colors).

  • Quantitative: Degree or intensity of stimuli (brightness levels).

Bottom-Up Processing

  • Begins at sensory receptors; perception occurs simply and directly.

  • Direct perception theory (Gibson, 1966); relies on texture gradients for proximity and depth.

  • Template Theories: Compare stimuli to stored templates for recognition.

  • Feature-Matching Theories: Recognizes objects based on specific features.

  • Recognition-by-Components (RBC) Theory: Breaks objects into simple components (geons).

Top-Down Processing

  • Construct: Interface of perception starts from existing knowledge.

  • Leverages context and prior experience influences object recognition.

  • Palmer (1975): Context affects recognition accuracy.

  • Semantic Regularities: Predictable patterns in scenes influence expectations.

Theories of Object Perception

  • Gestalt Principles: Mind organizes visual information into wholes.

    • Principles include Figure-ground, Proximity, Similarity, Closure, and Continuity.

  • Theory of Unconscious Inference: Perceptions shaped by prior knowledge.

Pattern Recognition Systems

  • Configurational System: Recognizes whole configurations (faces).

  • Feature Analysis System: Breaks down objects into parts for recognition.

  • Fusiform Gyrus in Temporal Lobe: Critical for facial recognition and expertise in specific item recognition.