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.