Sensation and Perception - Quick Review

Exam format and study tips

  • 34 questions, 35 minutes; open notes; no collaboration or AI use
  • Exams are generated from a question bank and are unique per student (order and options randomized)
  • Best help: TAs who did well; TA office hours listed on class site/announcements
  • Five exams total; your lowest grade is dropped

Sensation vs. perception

  • Sensation: intake of environmental energy via senses; raw data
  • Perception: brain’s interpretation/organization of that data
  • Often a mismatch: perception adds processing beyond sensation

Transduction and neural pathways

  • Receptors convert energy to neural signals (transduction)
  • Sensory nerves → central nervous system → thalamus (except smell) → cortex

Senses overview

  • Five traditional senses (vision, hearing, smell, taste, touch); some argue balance (equilibrium) and pain as additional senses
  • Vision is the primary focus in this course

Absolute thresholds and difference thresholds

  • Absolute threshold: smallest detectable stimulation, defined at ~50% detection
  • Examples (conceptual):
    • extVision:30ext{Vision: } 30 miles to detect a candle flame
    • extHearing:10ext{Hearing: } 10 feet to hear a mosquito
    • extSmell:1extdropofperfumeinalargespaceext{Smell: } 1 ext{ drop of perfume in a large space}
    • extTaste:1extteaspoonofsugarin2extgallonsofwaterext{Taste: } 1 ext{ teaspoon of sugar in } 2 ext{ gallons of water}
    • extTouch:aflywingontheskin(≈1extcm)ext{Touch: } a fly wing on the skin (≈1 ext{ cm})
  • Just noticeable difference (Weber’s law): smallest detectable difference between two stimuli
    • Formula: ΔII=k\frac{\Delta I}{I} = k
    • The noticeable difference grows with stimulus magnitude

Sensory adaptation

  • Receptors become less responsive to unchanging stimuli
  • Examples: odors, sounds, tastes; adaptation rates vary by sense
  • Odor adaptation ~2.5%2.5\% decrease per second

Visual system: light, eye, and retina

  • Light properties: wavelength (color) and amplitude (brightness)
  • Visible spectrum is a small portion of the electromagnetic spectrum
  • Eye anatomy (key parts): pupil, lens, iris, retina, fovea
  • Retina contains rods (high light sensitivity, peripheral; dark adaptation 20−3020-30 min) and cones (color/detail; concentrated in fovea; fast adaptation 2−32-3 min)
  • Fovea = center of gaze with high acuity; blind spot where optic nerve exits

Color vision theories

  • Young–Helmholtz (trichromatic) theory: three cone types (S blue, M green, L red); colors are combinations of cone activity
  • Opponent-process theory: higher-level processing; color perception in opposing channels (red–green, blue–yellow, black–white); explains afterimages
  • Both theories contribute at different levels; receptor-level color coding vs. post-receptor processing
  • Color blindness: red–green most common (especially in men); blue–yellow rare

Perception and processing: bottom-up vs top-down

  • Bottom-up: data-driven; use sensory features (color, brightness) to recognize
  • Top-down: using prior knowledge/expectations to interpret
  • Perception can be biased by context and expectations

Perceptual illusions and biases

  • Illusions reveal how context shapes perception (e.g., checkerboard/contrast effects)
  • Change blindness: failure to notice large changes in a scene; highlights limited attention and reliance on memory
  • Cocktail party/preconscious processing: unattended info can capture attention if personally relevant (e.g., name)
  • Figure-ground, grouping (Gestalt): group by similarity, proximity, continuity, closure

Depth perception and depth cues

  • Depth perception: crucial for interacting with the world
  • Binocular cues: rely on two eyes
    • Retinal disparity: different images on each retina; greater disparity for closer objects
    • Convergence: eye inward movement as objects get closer
  • Monocular cues: usable with one eye
    • Linear perspective, interposition, relative size, texture gradient
  • Visual illusions illustrate depth cues (e.g., Muller-Lyer, linear perspective effects)
  • Visual cliff studies show some depth perception is innate (nature) but much is learned (nurture)

Extrasensory perception (ESP)

  • Perception beyond ordinary senses; not scientifically demonstrated; current evidence is inconclusive

Taste, smell, and touch

  • Taste buds: ~10,00010{,}000; five basic tastes (sweet, sour, salty, bitter, umami)
  • Most flavor comes from smell; aging often reduces smell more than taste, affecting appetite
  • Texture contributes to flavor experience; fat has no taste by itself
  • Taste receptors and senses of touch/pain/temperature reside in the skin; somatosensory cortex maps show sensitivity differences across the body

Brief notes on MRI terminology (class context)

  • Functional MRI is used to measure brain activity over time; be aware of common acronym mix-ups (fMRI vs other terms)

Quick takeaway for exam readiness

  • Know the definitions: sensation vs perception; thresholds; Weber’s law; adaptation
  • Identify where signals go: eye pathways to thalamus and cortex; smell bypasses the thalamus
  • Distinguish theories: trichromatic vs opponent-process for color; know why both matter
  • Recall key depth cues and Gestalt principles
  • Be able to explain why perception can differ from sensation and how illusions illustrate this