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00 Introduction

What is Perception?

  • Begins with physical energy/chemical inputs → transformed into neural activity.
  • Neural activity provides cues → brain decodes the world.
  • Leads to:
    • Updating mental representation: What’s out there? Where is it?
    • Readiness for action → action alters the environment → perception-action loop.
  • Perception = link between mind and physical world.

Course Roadmap

  • Methods (psychophysics)
  • The Visual System
  • Higher-level regulation: attention & imagery
  • The Somatosensory System
  • The Auditory System
  • The Chemical Senses: Smell & Taste
  • Intersensory interactions
  • Modulators: impairment, development

Intuitions About Perception

1. Do we perceive reality as it really is?

  • No, perception is not veridical. It makes guesses using heuristics.
  • Illusions (size, shape, motion) reveal perceptual rules.
  • Bayesian model: brain predicts future states from current sensory data/statistics (e.g., tunnel illusion).

2. How long does it take to perceive?

  • Very fast: tens of milliseconds to see an object.
  • But sometimes slow (e.g., stereo vision may take minutes).
  • Reaction time depends on signal intensity (stronger → faster).
  • Reaction time decreases when more sensory inputs are presented simultaneously. → More sources = faster perception.
    • Hypothesis 1: Neural Integration
      • Inputs from different senses (e.g., shock + light) might combine in the nervous system.![[Screenshot 2025-08-27 at 3.39.38 PM.png]]
      • Combined intensity reaches threshold sooner → earlier response.
      • Question: Can fundamentally different modalities (like light and shock) really “sum”?
    • Hypothesis 2: Horse-Race Model
      • Each stimulus acts independently, like two horses racing.
      • Whichever stimulus “finishes first” (detected sooner) triggers the response.
      • On average, having more inputs means a higher chance of a faster one → reduced reaction time.
      • Limitation:
        • Purely statistical advantage explains some improvement, but not the full magnitude of speed-up observed experimentally.
        • Suggests both neural integration and statistical factors may contribute.

3. How many senses do we have?

  • More than 5
  • Each sense organ signals to multiple systems further “upstream” in the nervous system
  • Distinct systems for: “what” is there? & “where” is it?
  • Distinct systems compute successive levels of representation
    • Example of processing across different levels of representation in Vision: early pixels → regions/groups → object features → knowledge about objects.
  • Perceptual difficulties come from
    • detection: eg. detect something in noise field
    • parsing: breaking regions into features (eg. detect dogs in binary colors)
    • binding: putting regions together (eg. what edges go together? - 纪念碑谷)

4. Are we experts at perception?

  • Yes: speech, reading, and special interests show expert-level perception.