Sensation & Perception Module – Comprehensive Study Notes

Sensation and Perception: Foundational Distinction

• Sensation

  • Mechanical/biological registration of energy from the environment.

  • Sense organs collect data and deliver it to the brain for initial processing.

  • Immediate experiences described in raw qualities (e.g., hot, loud).

• Perception

  • Active cognitive interpretation of sensory data.

  • Brain selects, organizes, and assigns meaning; likened to “stitching a quilt,” not taking a photograph.

  • Produces experiences of coherent objects or events (form, order, meaning).

Three Core Principles (Apply Across All Senses)

• 1. Non-isomorphism between physical & psychological reality

  • No 1-to-1 copy of the outer world in the inner mind.

  • Relation is orderly enough to be expressible in equations (psychophysics) but not literal duplication.

  • Example: Pressure of a pin on skin vs. subjective pain/pressure.

• 2. Sensation & perception are active processes

  • Sensation = act of translation (transduction) from physical energy ⟶ neural code.

  • Perception organizes these codes; constant orientation to biologically relevant cues (sounds, smells, tastes).

• 3. They are adaptive (evolutionary perspective)

  • Sensory systems shaped to boost survival & reproduction.

  • All systems share: specific energy tuning, transduction, thresholds, decision making, adaptation to change.

Common Functional Features of Every Sensory System

• Transduction: specialized receptor cells convert stimulus energy → electrical signals.

• Thresholds

  • Below a limit nothing is sensed; above it becomes psychologically meaningful.

• Decision-Making Element

  • Organism must separate signal from irrelevant noise (e.g., nighttime creak).

• Change Sensitivity

  • Detect variations (heavier grocery bag, louder tone). Underlies difference threshold.

• Sensory Adaptation

  • Receptors reduce firing to unchanging input (e.g., brewery sulphur smell, watch on wrist).

Psychophysics: Measuring the Mind–Stimulus Link

• Field studying lawful mappings of stimulus intensity → psychological experience.

• Absolute Threshold (AT)

  • Minimum stimulus magnitude detected 50 % of the time (no sharp jump from 0 % → 100 %).

  • Classic estimates:

  • Hearing: ticking watch @ 6 m in quiet.

  • Smell: 1 perfume drop in an entire house.

  • Taste: 1 tsp sugar / 4 L water.

  • Touch: fly wing on cheek @ 1 cm.

  • Vision: candle flame @ 60 km on dark, clear night.

  • Varies by individual, day-to-day state (fatigue).

• Difference Threshold / Just Noticeable Difference (JND)

  • Smallest change in stimulus intensity reliably detected.

  • Context-dependent; anchors further laws (Weber, Fechner, Stevens).

Weber’s Law

• \frac{\Delta I}{I}=k

  • Constant proportion k unique per modality (heaviness ≈ \frac1{50}, loudness @ middle C ≈ \frac1{10}).

  • Explains why adding 0.5 kg to 1 kg backpack obvious, but not to 30 kg pack.

Fechner’s Log Law

• Subjective sensation S=k \log I (arithmetical growth in S corresponds to logarithmic growth in physical I).

  • Small early increases feel large; later huge increases feel small.

Stevens’ Power Law

• S = k I^{n}

  • Exponent n varies by sense (<1 for brightness n=0.33; >1 for pain, electric shock).

  • Generalizes Fechner & handles cases where sensitivity grows faster (pain) or slower (brightness) than logarithmic.

Signal Detection Theory (SDT)

• Replaces fixed threshold with detectability (sensitivity + decision criterion).

• Two Processes

  1. Sensory (how well the signal is encoded).

  2. Decision (response bias—readiness to say "yes").

• Outcomes

  • Hit ✅ | Miss ❌ | False Alarm ❗ | Correct Rejection ✅.

• ROC Curve (Receiver Operating Characteristic)

  • Plots hit rate vs. false-alarm rate across criteria.

  • Lines A (chance), B (moderate sensitivity), C (high sensitivity).

  • Area Under Curve (AUC) quantifies accuracy.

• Response Bias Influences

  • Expectations (doctor primed by heart-pain complaints).

  • Motivation/costs (surgeon avoiding missed tumor vs. unnecessary surgery).

  • Dynamic example: pizza delivery at party—criterion shifts as expected arrival nears.

• Used in aviation, radiology, security screening, etc.

Vision: Transforming Light to Sight

Nature of Light

• Electromagnetic radiation; eyes tuned to narrow visible spectrum.

• Wavelength → Hue (color), Amplitude → Brightness, Purity → Saturation.

• Light advantageous: travels ~3\times10^{8}\,\text{m/s}, straight lines, reflects/absorbs creating patterns.

Optical Focusing Apparatus

• Cornea: transparent, curved, protective; first refraction.

• Aqueous Humor: clear fluid feeding cornea/lens.

• Pupil: adjustable aperture; Iris muscle constricts/dilates (dim light → dilation; bright → constriction for sharpness).

• Lens: elastic oval; accommodation – changes thickness to keep retinal image sharp (felt as eye strain when finger approaches nose).

• Vitreous Humor: gelatinous interior that light crosses en route to retina.

Retina: Transduction Layer

• Paper-thin neural tissue at eye’s rear.

• Fovea: center of sharp vision; densely packed cones only.

• Blind Spot (Optic Disc): no receptors where optic nerve exits; perceptual filling-in + binocular overlap erase holes.

Photoreceptors

• Cones

  • Color, fine detail, bright light.

  • 3 biochemical types sensitive to ~420 nm (blue), ~530 nm (green), ~560 nm (red).

• Rods

  • Highly light-sensitive, B/W vision, motion, periphery.

  • Dark adaptation ~15 min; cones adapt ~4–5 min.

Retinal Circuitry

• Rods/cones → bipolar cells → ganglion cells.

• Ganglion axons bundle = optic nerve.

• Each ganglion cell has a receptive field: region within which light elicits firing.

Central Visual Pathways

• Optic nerve → optic chiasm (nasal fibers cross) → optic tracts.

• Major route: optic tract → lateral geniculate nucleus (LGN) of thalamus → primary visual cortex (V1/striate).

• Minor route: optic tract → superior colliculus (eye movements; unconscious orientation).

• Blindsight: damage to V1 causes conscious blindness, yet SC/LGN route supports accurate but unconscious localization.

• Beyond V1 two streams:

  • "What" (ventral): V1 → inferior temporal lobe (object identification).

  • "Where" / "How" (dorsal): V1 → parietal lobe (spatial location, motion, action guidance).

Color Vision Theories

1. Trichromatic (Young–Helmholtz)

   • Three cone types (R/G/B) combine → all colors via additive mixing.

   • Explains basic color matching but fails for after-images & yellow.

2. Opponent Process (Hering)

   • 3 antagonistic pairs within post-receptor network: Red↔Green, Blue↔Yellow, Black↔White.

   • Explains complementary after-images (staring at green → red after-image) & presence of yellow without "reddish-green" mixtures.

• Modern view: trichromacy at receptor level, opponent coding at ganglion/LGN/V1 level (two-stage model).

Quick Review Items (From Lecture Quizzes)

• Sensation = information gathered by the senses.

• Response bias shaped by expectations + motivation.

• Sensory adaptation = receptor response decrease to constant stimulus.

• Two key eye processes: focusing + transduction.

• A ganglion’s receptive field = region where light affects its firing.

• Post-V1 information diverges along what & where streams.

Metaphors, Examples, & Real-World Links

• Quilt vs. photograph (perception stitches fragments into meaningful wholes).

• Autistic boy hiding from search-and-rescue helicopters illustrates need to understand individual perceptual worlds.

• Pizza-delivery SDT scenario: changing pay-off matrix affects criterion.

• Add 5¢ coin to light envelope vs. full purse = JND demonstration.

• Dark-room adaptation: rods slowly regenerate photopigment; cones adapt first but become useless under very low light.

Ethical & Practical Implications

• Training/info delivery must exceed absolute thresholds (e.g., safety alarms).

• Clinical contexts: misreading sensory signs (tumor, heart murmurs) balances false alarms vs. misses.

• Early intervention critical in developmental, aging, or injury-related perceptual deficits.

Key Equations & Numerical Facts (LaTeX-formatted)

• Weber: \frac{\Delta I}{I}=k.

• Fechner: S = k\,\log I.

• Stevens: S = k I^{n} (e.g., brightness n=0.33; pain n>1).

• Light speed: 3\times10^{8}\,\text{m/s}.

• Dark adaptation times: cones ≈ 4\text{–}5\,\text{min}; rods ≈ 15\,\text{min}.

• Classical absolute thresholds (50 % detection): candle 60\,\text{km} away; perfume drop per house; fly wing 1 cm, etc.

These bullet-point notes capture every major & minor lecture item, definitions, examples, formulas, real-world connections, and quiz clarifications. They provide a full, organized substitute for the original transcript.