Sensation and Perception – Chapter 3 (Hockenbury & Nolan, 10th ed.)

Definition of Sensation & Perception

• Sensation – detection of physical energy (light, sound, pressure, heat, chemical) by specialized receptor cells that convert that energy into neural impulses.

• Perception – integration, organization, and interpretation of those sensory impulses, producing conscious experience.

• Key distinction: sensation = raw data acquisition; perception = meaningful interpretation (e.g., hearing pressure changes vs. recognizing a melody).

Basic Principles of Sensation

• Theme: All sensation begins with physical energy → sense receptor → neural impulse → brain.

Sensory Receptors & Transduction

• Sensory receptors – unique cells in each organ (rods, cones, hair cells, taste-bud cells, etc.).

• Transduction – biochemical process that converts physical energy into coded neural signals the CNS can understand.

• Pathway summary: Environmental energy → receptor membrane potential change → action potentials → specific sensory pathway → cortex → PERCEPTION.

Sensory Thresholds

• A stimulus must reach the receptor’s threshold to be detected.

Absolute Thresholds

• Minimum stimulation needed to consciously detect a stimulus 50\% of the time.

  • Vision: candle flame at 30 miles on a dark, clear night.

  • Hearing: watch tick at 20\,ft in quiet.

  • Taste: 1 tsp sugar in 2 gal water.

  • Smell: one drop perfume diffused through a 3-room apartment.

  • Touch: bee’s wing falling 0.5\,in onto cheek.

Difference Threshold (Just Noticeable Difference, JND)

• Smallest change in stimulation required to detect a difference.

• Weber’s Law – JND is a constant proportion k of the original stimulus intensity S.
  \Delta S = kS or in logarithmic form \Psi = k \log S ((\Psi) = sensation magnitude).

• Fechner’s extension integrates all JNDs to describe total perceived intensity; reflects non-linear relationship between physical & psychological magnitude.

Sensory Adaptation

• Prolonged, constant stimulation ➝ declining receptor response and diminished conscious sensation (e.g., clothes on skin, background hum).

Vision

Physical Properties of Light

• Light = electromagnetic radiation; described by wavelength (distance peak-to-peak) and amplitude.

• Perceptual correlates:

  • Wavelength ➝ Hue (color name).

  • Purity of wavelength ➝ Saturation.

  • Amplitude ➝ Brightness.

Anatomy of the Eye & Path of Light

• Cornea – fixed curved surface; begins focusing.

• Pupil – adjustable aperture within iris; size varies with light & arousal.

• Lens – elastic; performs accommodation (changes curvature) to focus near vs. far objects onto the retina.

• Retina – thin neural tissue lining back wall; contains photoreceptors.

• Fovea – central pit, all cones, point of greatest acuity.

• Optic disk / blind spot – no receptors where optic nerve exits; brain “fills in.”

Photoreceptors

• Rods (~120\text{ million})

  • Long, thin; extreme light sensitivity; grayscale vision; peripheral & night vision; none in fovea.

• Cones (~6\text{ million})

  • Short, tapered; require more light; encode color; concentrated in fovea ➝ high visual acuity.

Retinal Processing & Visual Pathways

• Bipolar cells collect signals from rods/cones ➝ ganglion cells.

• Each ganglion cell has a receptive field; rod inputs are pooled (many:1) ➝ low detail; cone inputs few:1 ➝ high detail.

• Axons of ganglion cells form optic nerve.

• Optic nerves meet at optic chiasm: nasal fibers cross, temporal stay ipsilateral ➝ thalamus (LGN) ➝ primary visual cortex (V1).

• Cortical segregation:

  • Ventral stream (“what”) ➝ temporal lobe, object identity.

  • Dorsal stream (“where/how”) ➝ parietal lobe, spatial location & action.

• Blindsight – V1 damage can leave dorsal/ventral sub-paths partially functional ➝ unconscious vision.

Synesthesia

• Involuntary, consistent blending of senses (e.g., grapheme-color, sound-taste).

• fMRI & connectivity studies (Ramachandran, Cytowic) suggest hyper-connectivity among sensory cortical areas.

Color Vision Theories

• Trichromatic Theory (Young–Helmholtz)

  • Three cone types tuned to long (red), medium (green), short (blue) wavelengths.

  • Explains color mixing & red-green color blindness.

• Opponent-Process Theory (Hering)

  • Post-receptor channels antagonistic: red ↔ green, blue ↔ yellow, black ↔ white.

  • Explains after-images & color contrast.

• Modern view: trichromatic coding at receptor level ➝ opponent processing in ganglion, LGN, and cortex.

Visual Phenomena & Disorders

• Red–green color blindness – missing/abnormal L or M cones; blue perception intact.

• Myopia – focus in front of retina; distant blur. Hyperopia – focus behind retina; near blur.

• Accommodation declines with age (presbyopia).

Hearing

Physical Properties of Sound

• Sound wave – variation in air pressure.

  • Amplitude ➝ Loudness (decibels, \text{dB}).

  • Frequency ➝ Pitch (Hertz, \text{Hz});

  • Humans hear 20{-}20{,}000\,\text{Hz}.

  • Complexity ➝ Timbre (quality; allows piano vs. sax to be distinguished on same note).

Decibel Reference Table

• 0\,\text{dB} – threshold of hearing.

• 70\,\text{dB} – busy traffic; prolonged exposure begins risk.

• 90\,\text{dB} – lawn mower; >8 hr unsafe.

• 120\,\text{dB} – rock concert; immediate damage.

• 140\,\text{dB} – jet engine/shotgun; any exposure unsafe.

Ear Anatomy & Path of Sound

1. Outer ear – pinna collects waves ➝ auditory canal ➝ eardrum (tympanic membrane).

2. Middle ear – ossicles: hammer (malleus), anvil (incus), stirrup (stapes) amplify vibration; stirrup pushes on oval window.

3. Inner ear – cochlea (fluid-filled spiral): oval window vibration ➝ fluid waves ➝ basilar membrane motion ➝ bending of hair-cell cilia against tectorial membrane ➝ transduction.

4. Neural impulses along auditory nerve ➝ thalamus ➝ primary auditory cortex (temporal lobe).

• Round window flexes to relieve fluid pressure.

Pitch-Coding Theories

• Frequency Theory – entire basilar membrane vibrates at same frequency; hair cells fire volleys; explains low pitches (<\approx 1000\,\text{Hz}).

• Volley Principle – groups of neurons alternate firing to reach higher combined rates.

• Place Theory – specific location of maximal membrane displacement encodes frequency; best for high pitches (>\approx 5000\,\text{Hz}); cochlea is tonotopic (base = high, apex = low).

• Intermediate frequencies use combination of both.

Hearing Loss

• Conduction deafness – ossicle or eardrum damage; hearing aid helps.

• Nerve (sensorineural) deafness – hair cell damage (e.g., loud noise); cochlear implant bypasses receptor.

Chemical & Body Senses

Olfaction (Smell)

• Odorant molecules bind to receptors in nasal epithelium ➝ axons form olfactory nerve ➝ olfactory bulb (brain’s front) ➝ projections to temporal lobe (conscious ID) & limbic system (emotion/memory).

• Direct cortical route (no thalamic relay); function declines with age & disease.

Gustation (Taste)

• Taste buds (~10{,}000) embedded in tongue papillae; each bud ≈ 50 receptor cells with microvilli projecting into taste pore.

• Five primary tastes ➝ sweet, sour, salty, bitter, umami (MSG/protein).

• “Tongue map” is myth; all regions can detect all tastes but with differing densities.

Touch & Temperature

• Skin houses multiple receptors (pressure, vibration, stretch, temperature).

• Distribution uneven; areas needing fine control (fingertips, lips) have high receptor density.

Pain

• Nociceptors – free nerve endings in skin, muscle, organs.

• Two fiber systems:

  • Fast (A-delta) – sharp, localized pain; myelinated.

  • Slow (C) – dull, throbbing, emotional pain; unmyelinated.

• Gate-Control Theory (Melzack & Wall) – spinal “gate” modulates pain signals; inputs from brain (attention, emotion, endorphins) and competing touch signals can open/close gate.

• Sensitization – chronic activation increases pathway responsiveness (opposite of adaptation) ➝ chronic pain, phantom limb.

• Pain perception routes: sensory (somatosensory cortex) + affective (limbic) components.

Factors Modulating Pain Gates

• Intensify: anxiety, fear, helplessness, negative mood, social contagion.

• Reduce: control, positive mood, relaxation, endogenous opioids (endorphin, enkephalin), supportive context.

Proprioception & Vestibular Sense

• Proprioceptors in muscles/joints signal limb position & movement.

• Vestibular organs (semicircular canals & vestibular sacs in inner ear) detect head rotation, linear acceleration, gravity ➝ balance & spatial orientation.

Perception Processes

Bottom-Up vs. Top-Down

• Bottom-up – data-driven; build perception from sensory elements (feature detectors).

• Top-down – concept-driven; expectations, knowledge, culture shape interpretation (e.g., reading messy handwriting, cultural focus on context vs. object).

Cultural Influences

• Chua et al.: U.S. students fixate on focal object; Chinese students scan background ➝ holistic vs. analytic perception.

Gestalt Principles of Organization

• Figure–Ground – automatic segregation of figure (focus) & background; reversible figures illustrate ambiguity.

• Grouping rules (illustrated by dots/lines icons):

  • Similarity – alike items grouped.

  • Proximity – close items grouped.

  • Continuity – smooth paths preferred.

  • Closure – fill gaps to see whole.

  • Symmetry – balanced forms favored.

Depth Perception

Monocular Cues (single eye sufficient)

• Relative size, Overlap (interposition), Aerial perspective (haze), Texture gradient, Linear perspective, Relative height, Motion parallax (near objects move faster across retina).

Binocular Cues (require both eyes)

• Convergence – eye muscle strain; more rotation = closer object.

• Binocular (retinal) disparity – positional difference of images; greater disparity = nearer.

Motion Perception

• Expanding retinal image ➝ object approaching; rate of expansion estimates speed.

• Specialized cortical neurons code specific directions & speeds.

Perceptual Constancies

• Size constancy – perceive actual size despite retinal image change.

• Shape constancy – door viewed at angle still “rectangular.”

Perceptual Illusions

• Müller-Lyer – arrows influence size-distance scaling (carpentered-world hypothesis: experience with right angles enhances illusion susceptibility).

• Moon illusion – horizon moon appears larger due to perceived distance & context cues.

Perceptual Sets & Face Bias

• Expectancy frame guides interpretation; usually aids accuracy but can cause false positives (seeing faces in clouds).

Extrasensory Perception (ESP)

• Proposed perception without sensory input: telepathy, clairvoyance, precognition, psychokinesis.

• Studied by parapsychology; empirical support weak/inconclusive.

Pain Management Strategies

• Clinically & self-administered aides: hypnosis, analgesics, biofeedback, acupuncture plus everyday distraction, guided imagery, relaxation, meditation, positive self-talk, cognitive reappraisal.

Summary Table of Senses (condensed)

• Hearing – sound waves – ear – hair cells (cochlea)

• Vision – light – eye – rods & cones (retina)

• Smell – airborne molecules – nose – olfactory cilia

• Taste – dissolved chemicals – tongue – taste-bud receptors

• Touch – pressure – skin – Pacinian corpuscles, etc.

• Pain – tissue damage – widespread – nociceptors

• Proprioception – muscle stretch – muscles/joints – proprioceptors

• Vestibular – gravity/motion – semicircular canals/sacs – hair-cell receptors

Key Equations & Numbers (LaTeX format)

• Weber’s Law: \Delta S = k S

• Fechner/Log Law: \Psi = k \log S

• Hearing range: 20{-}20{,}000\,\text{Hz}

• Hazardous sound level begins ≈ 85\,\text{dB}

• Visible light wavelength ≈ 400{-}700\,\text{nm}

These bullet-point notes consolidate every major and minor point from Chapter 3’s transcript, blending definitions, mechanisms, theories, numerical values, examples, cultural & clinical implications, and mnemonic comparisons to serve as a stand-alone study guide on Sensation and Perception.