Sensation and Perception – Comprehensive Exam Notes

Sensation vs. Perception

• Sensation: “The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.”
  • Raw data intake; bottoms-up flow from sense organs ➜ brain.
• Perception: “The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.”
  • Adds meaning; heavily top-down (concept-driven).
• The brain therefore has a dual role:
  • Receives physical input (sensation).
  • Makes sense of, filters, and labels that input (perception).

Bottom-Up & Top-Down Processing

• Bottom-Up Processing
  • Begins with sensory receptors; works up toward integration in the brain.
  • Answers “What am I seeing?”
• Top-Down Processing
  • Uses experience, expectations, and context to interpret sensory data.
  • Answers “Is that something I’ve seen before?”
• Demonstrations
  • 3-D bottle/hidden dolphins illusion: Kids’ limited adult imagery ➜ see dolphins, not erotic scene (top-down difference).
  • Dalmatian picture: priming with words “tree, sidewalk, dog, Dalmatian” enables figure detection.

From Sensory Organs to the Brain

1. Reception – Stimulus energy (light, sound, heat, pressure, chemicals) stimulates receptor cells.
2. Transduction – \text{stimulus energy} \rightarrow \text{neural impulses}.
3. Transmission – Neural information travels to specific brain areas for further processing.

Thresholds

• Absolute Threshold: Minimum stimulus intensity needed for detection 50\% of the time.
  • Anything below = subliminal.
• Subliminal Effects
  • Cannot teach complex information but can prime attitudes/choices (e.g., preference for side that flashed a nude image briefly).
• Signal Detection Theory (SDT)
  • Detecting stimulus ≠ purely intensity based; influenced by experience, expectations, motivation, alertness.
  • Explains why “absolute” thresholds fluctuate.

Sensory Adaptation

• Constant stimulation ➜ decreased responsiveness.
  • E.g., rock in shoe, ticking clock fade from awareness.
• Vision usually immune because eyes constantly move; immobilizing gaze reveals fading patches.

Perceptual Set & Context Effects

• Perceptual Set: A mental predisposition to perceive one thing and not another (top-down).
  • “Loch Ness monster vs. tree branch,” “flying saucers vs. clouds.”
  • Can be primed by prior cues, words, or ambiguous stimuli.
• Context Effects
  • Same stimulus perceived differently in different contexts.
  • Dot-in-circle size illusion; spelling test “pair/pear/payer” choices shaped by sentence.

Emotion, Physical State & Motivation

• Fatigue ➜ destinations seem farther.
• Heavy crossbow ➜ target appears farther.
• Backpack/sad music/solitude ➜ hill looks steeper.
• Desired objects (water, money) appear closer.

Vision: Energy, Sensation, Eye Anatomy

• Visible Spectrum: Portion of electromagnetic waves detectable by eye; brain converts to color.
• Wave Properties
  • Wavelength/frequency ➜ hue (color).
  • Amplitude ➜ brightness (intensity).
• Pathway
  1. Light passes cornea ➜ pupil.
  2. Lens focuses & inverts; adjusts shape (accommodation).
  3. Image lands on retina ➜ start transduction.
  4. Signals leave via optic nerve.
• Feature Detection
  • Certain retinal ganglion cells & cortical neurons (supercells) respond to edges, lines, motion, faces.

Color Vision Theories

1. Young-Helmholtz Trichromatic Theory
   • Three receptor cones: red, green, blue; all colors from their combinations.
2. Opponent-Process Theory
   • Opposing retinal processes: red vs. green, blue vs. yellow, white vs. black.
   • Explains after-images & color blindness (missing/defective red-green cones).

Perceptual Organization (Gestalt Principles)

• We automatically organize sensations into wholes (Gestalts).
  • Figure–Ground: Objects (figures) separated from background.
  • Grouping Principles:
  • Proximity – nearby items grouped.
  • Continuity – perceive continuous patterns.
  • Closure – fill gaps to create whole objects.
• Brain interprets ambiguous blue-dot cube as multiple possible organizations (holes vs. floating cube).

Depth Perception

• Visual Cliff studies show crawling babies & newborn animals avoid apparent drop ➜ innate depth cues.
• Binocular Cues
  • Retinal Disparity: Greater difference between images = closer object.
• Monocular Cues (one eye sufficient)
  • Interposition: Blocking object = closer.
  • Relative Size: Smaller familiar object = farther.
  • Linear Perspective: Converging lines = distance.
  • Relative Height: Objects higher in field = farther.
  • Shading/Light & Shadow: Patterns of light create 3-D texture.
  • Relative Motion (Motion Parallax): Farther objects move slower across retina when we move.

Perceptual Constancies & Visual Illusions

• Perceptual Constancy: Stable perception despite changing sensory data (top-down).
  • Color Constancy: Evaluate color relative to surroundings; adjust for lighting.
  • Brightness Constancy: Squares A & B identical gray but shadow context alters perception.
  • Shape Constancy: Door remains rectangle while opening.
  • Size Constancy & Moon Illusion: Moon seems larger on horizon due to distance cues; Ames room manipulates cues to alter perceived size.

Audition: Physical Energy ➜ Perception

• Frequency (Hz) ➜ perceived Pitch (high/low).
• Amplitude (dB) ➜ perceived Loudness (loud/soft).
• Complexity ➜ perceived Timbre (sound quality).

Ear Anatomy & Hearing Process

1. Outer Ear: Collects sound; funnels to eardrum.
2. Middle Ear: Hammer, anvil, stirrup amplify vibrations ➜ oval window.
3. Inner Ear (Cochlea): Fluid waves bend hair cells ➜ transduction ➜ auditory nerve ➜ temporal lobe.

• Hearing Loss Prevention
  • Extended exposure > 85\ \text{dB} damages hair cells.
  • Treat infections, limit volume to below conversation-blocking level.

Pitch Perception Theories

• Place Theory: High frequencies stimulate different places along basilar membrane.
• Frequency Theory: Low frequencies cause hair cells to fire at same rate as sound waves.
• Volley Principle: Combined firing of alternate groups achieves higher overall firing rates for ultra-high frequencies.
• Loudness Coding: Intensity ➜ more (and neighboring) hair cells fire.

Taste (Gustation)

• Five Basic Tastes & Evolutionary Roles
  • Sweet: energy source.
  • Sour: possible acids/toxins.
  • Salty: sodium for physiology.
  • Bitter: potential poisons.
  • Umami (savory): proteins for growth/repair.
• Biology
  • Taste buds contain receptor cells with hair-like projections.
  • Receptors regenerate ~every 1–2 weeks; decline with age.
  • Top-down expectation modifies flavor (e.g., colored drinks).

Sensory Interaction & Synaesthesia

• Sensory Interaction: One sense alters another.
  • Sound flashes enhance visual detection; flavor combines taste + smell + texture; lip-reading influences heard speech.
• Synaesthesia: Cross-modal triggering (e.g., numbers ➜ colors, sounds ➜ tastes); stable trait in some individuals.

Body Position & Balance

• Kinesthesis
  • Sense of body part position & movement via receptors in muscles/joints.
  • Essential for coordinated action without constant visual guidance.
• Vestibular Sense
  • Monitors head’s position relative to gravity; governs balance.
  • Structures: semicircular canals & vestibular sacs with fluid & hair receptors; signals ➜ cerebellum.
  • Acts like internal gyroscope keeping body upright.