Psychology Sensation and Perception: Key Concepts and Theories

Prosopagnosia

"Face blindness"—neurological disorder where individuals can't recognize familiar faces despite normal vision. Caused by damage to fusiform face area; shows perception requires specialized brain processing beyond basic sensation.

Sensation vs. Perception

Sensation: Process by which sensory receptors detect physical energy (light, sound) from environment—raw input stage. Perception: Brain organizes/interprets sensations into meaningful experiences (e.g., light waves → "apple").

Bottom-up processing

Data-driven perception starting with individual sensory elements building to whole (e.g., recognizing word by sounding out letters). Opposite of top-down; pure sensory analysis without prior knowledge.

Top-down processing

Concept-driven perception using expectations, context, knowledge to interpret sensory data (e.g., misreading "the" as "they" in sentence). Combines with bottom-up for efficient recognition.

Selective attention

Focusing conscious awareness on specific stimuli while ignoring others. Key for filtering overload; examples include inattentional blindness (miss gorilla in video), change blindness (undetected scene swaps).

Cocktail party effect

Ability to selectively attend to one conversation amid noise by suddenly noticing your name in another. Demonstrates involuntary attention shift to personally relevant info.

Transduction

Conversion of physical stimuli (light/sound waves) into electrochemical neural impulses. First step in sensation; retina transduces photons, cochlea transduces vibrations.

Psychophysics

Study linking physical stimulus properties to psychological sensations. Measures thresholds, adaptation; foundational for understanding detection limits.

Absolute threshold

Minimum stimulus intensity detected 50% of time (e.g., single candle 30 miles away on dark night). Theoretical detection limit accounting for chance.

Difference threshold (JND)

Smallest change in stimulus detectable 50% of time. Varies by sense/stimulus strength; basis for Weber's Law.

Signal detection theory

Explains detection varying by signal strength, noise, and personal factors (motivation, fatigue). Outcomes: hits, misses, false alarms, correct rejections; applied to real-world (e.g., radar operators).

Subliminal stimuli

Below absolute threshold; too weak for conscious detection but may unconsciously influence (e.g., flashed words). Limited effects; not powerful for behavior change.

Priming

Exposure to one stimulus influences response to another (e.g., "bread" speeds "butter" recognition). Shows unconscious processing effects.

Weber's Law

Just noticeable difference (JND) proportional to stimulus magnitude. Formula: ΔI/I = k (constant); e.g., 5% lighter weight noticeable regardless of base weight.

Sensory adaptation

Decreased sensitivity to constant stimulus due to receptor fatigue (e.g., entering smelly room—odor fades). Protects from overload; differs from habituation.

Habituation

Reduced behavioral response to repeated irrelevant stimulus (e.g., ignoring clock tick). Cognitive/attentional; not receptor-based like adaptation.

Light wavelength and hue

Wavelength determines hue/color (short=blue/violet, long=red; 400-700nm visible). Intensity/amplitude sets brightness.

Eye pathway to brain

Cornea (bends light) → Pupil (opening) → Iris (controls size) → Lens (focus) → Retina (fovea sharpest; rods=dim/b&w, cones=color/detail → bipolar cells → ganglion cells → blind spot → optic nerve → occipital lobe).

Accommodation

Lens thickens/thins via ciliary muscles to focus near/far objects on retina. Aging reduces flexibility (presbyopia).

Feature detectors

Occipital lobe neurons responding to specific visual features (edges, motion). Hubel/Wiesel Nobel work; build complex perceptions hierarchically.

Parallel processing

Simultaneous processing of visual info (color, form, motion) via separate brain pathways. Enables quick, integrated vision.

Trichromatic theory

Young-Helmholtz: Color vision from 3 cone types (short= blue, med=green, long=red). Explains mixing but not afterimages.

Opponent-process theory

Hering: 3 opposing pairs (red-green, blue-yellow, black-white). Explains afterimages (stare green → see red); works with trichromatic.

Sound waves properties

Frequency/pitch (Hz; high freq=high pitch). Amplitude/loudness (decibels; 0=threshold, 120=pain).

Hearing pathway

Pinna/outer ear → auditory canal → eardrum → middle ear (hammer/anvil/stirrup amplify → oval window) → cochlea (fluid vibrates basilar membrane → hair cells/Organ of Corti → auditory nerve → temporal lobe).

Conductive vs. sensorineural hearing loss

Conductive: Outer/middle ear damage (e.g., earwax, bones); fixable. Sensorineural: Inner ear/nerve (age/noise); cochlear implants bypass.

Cochlear implant

Electronic device for sensorineural loss; mic → processor → electrode array stimulates auditory nerve directly.

Place theory of pitch

High pitches activate hair cells at cochlea base, low at apex. Basilar membrane tonotopic map.

Frequency theory of pitch

Nerve fires at sound frequency (up to 1000Hz); volley theory for higher. Explains low pitches.

Skin senses

Largest organ detects pressure (Meissner), warm/cold, pain (nociceptors). Gate-control theory: Spinal "gates" open/close pain signals via brain signals/other touch.

Taste (gustation)

5+ basic: sweet, sour, salty, bitter, umami (savory), oleogustus (fat). Papillae contain taste buds; all tongue areas detect all.

Olfactory system

Smell bypasses thalamus to olfactory bulb/cortex near hippocampus (strong memory link). Closely tied to taste (90% flavor).

Kinesthesia & vestibular sense

Kinesthesia: Body position/movement via muscles/tendons/joints. Vestibular: Balance via semicircular canals/otoliths in inner ear.

Sensory interaction & synesthesia

Senses influence each other (e.g., pink smells sweet). Synesthesia: Crossed wires (e.g., taste colors); McGurk effect (vision alters heard speech).

Perceptual set

Mental predisposition influencing interpretation (schemas, expectations). E.g., hungry sees food shapes in clouds.

Context, emotion, motivation effects

Context clues meaning (e.g., "bank" river/money). Emotion/motivation bias (fear amplifies threats).

Visual capture

Vision dominates other senses (e.g., ventriloquism—sound seems from mouth).

Gestalt principles

Organization rules: proximity (near=group), similarity (like together), continuity (smooth paths), closure (fill gaps), simplicity/common fate.

Figure-ground

Separate object (figure) from background (ground); reversible (Rubin vase/faces).

Binocular depth cues

Retinal disparity (3D diff between eyes). Convergence (inward eye turn for near).

Monocular depth cues

Relative size (smaller=distant), height (higher=distant), linear perspective, relative motion (parallax), interposition, light/shadow.

Motion perception

Apparent: stroboscopic (movies), phi phenomenon (lights chase), autokinetic (fixed light seems to move).

Perceptual constancies

Stable perception despite changes: color (white paper in sun/shade), shape (door rectangular tilted), size (distant person same height).

Perceptual adaptation

Brain adjusts to altered input (e.g., upside-down goggles—adapt in days). Shows plasticity.

Extrasensory perception (ESP)

Telepathy (mind-mind), clairvoyance (see distant), precognition (future). Parapsychology lacks replicable evidence; pseudoscience.