(A.K.A. “How your body’s IoT sensors turn photons & pressure waves into first-gen brain packets”)
| Concept | Core Idea | 1-Sentence AP Takeaway |
|---|---|---|
| Transduction | Converting physical energy → neural code | Rods & cones flip light into action potentials; hair cells flip vibration into APs. |
| Absolute Threshold | Min. stimulus 50 % of the time (Fechner) | Hearing test “beep” volume is finding your auditory AT. |
| Difference Threshold (JND) | Smallest detectable change (Weber’s Law) | You notice a 2 % volume bump, not a 0.2 %. |
| Sensory Adaptation | Receptor firing ↓ for constant input | Forget your watch is on your wrist after 2 min. |
| Signal Detection Theory | Sensation ≠ perception; hits vs. false alarms | Security screener’s “bias + sensitivity” model. |
1. Vision ― The MVP of AP Exams
| Layer | Key Cells / Parts | Function Nugget |
|---|---|---|
| Cornea / Lens | — | Accommodation bends light to retina |
| Retina | Rods (low light, periphery) / Cones (color, fovea) | Begin transduction |
| Bipolar → Ganglion → Optic Nerve | — | Axons form the optic nerve; blind spot where they exit |
| Optic Chiasm | — | Left visual field → right hemisphere & vice versa |
| Visual Cortex (Occipital) | Feature detectors (Hubel & Wiesel) | Edges, angles, movement |
Color Coding:
Young-Helmholtz (Trichromatic): RGB cones mix.
Opponent-Process (Hering): R-G, B-Y, B-W afterimages (explains flag illusion).
2. Audition ― Pressure Waves to Playlist
Outer Ear: Pinna → auditory canal
Middle Ear: Tympanic membrane vibrates ossicles (hammer, anvil, stirrup) striking oval window.
Inner Ear: Cochlea’s basilar membrane wave bends hair cells → auditory nerve (cranial VIII).
Pitch Codes
Place Theory: high freq = base of cochlea.
Frequency (Volley) Theory: firing rate mirrors low freq.
3. Other Modalities
| Sense | Receptors | Brain Path | Cool AP Hook |
|---|---|---|---|
| Touch (Somatosensation) | Free nerve endings, Merkel, Pacinian, etc. | Spinal cord → thalamus → parietal | Gate-Control Theory of pain (Melzack & Wall) |
| Taste (Gustation) | 5 basic flavors on taste buds | Medulla → thalamus → cortex | Receptor regrows every ~10 days |
| Smell (Olfaction) | Olfactory cilia in nasal epithelium | Direct to limbic (no thalamus!) | Smell = strongest emotion trigger |
| Kinesthetic | Stretch & tendon receptors | Parietal cortex | Know body part position |
| Vestibular | Semicircular canals & otoliths | Cerebellum & brainstem | Fluid shift → dizziness |
10 AP-Style MCQs
Transduction in the retina occurs in the:
A. Ganglion cells B. Rods & cones C. Optic nerve D. Lens E. Bipolar cellsWeber’s Law states that two stimuli must differ by a constant:
A. Frequency B. Ratio C. Decibel level D. Voltage E. Absolute valueDamage to the basilar membrane is likely to cause:
A. Conduction deafness B. Sensorineural deafness C. Tinnitus only D. Increased pitch perception E. Phantom limb painAfter staring at a red image and then looking at a white wall, you see green. This supports:
A. Trichromatic theory B. Gate-control theory C. Opponent-process theory D. Place theory E. Frequency theorySignal detection theory explains why a tired new parent may still wake to a faint baby cry because detection depends on:
A. Absolute threshold only B. Stimulus intensity only C. Expectation and motivation D. Sensory adaptation E. Sensory gating in spinal cordWhich receptor type is correctly matched with its sense?
A. Semicircular canal → kinesthetic B. Otolith → vestibular C. Hair cell in cochlea → vision D. Olfactory bulb → gustation E. Pacinian corpuscle → smellThe point where the optic nerve leaves the eye creates:
A. Fovea B. Blind spot C. Macula D. Dark adaptation E. Depth perceptionA person who can hear normally but whose eardrum is damaged might suffer from:
A. Conduction hearing loss B. Sensorineural hearing loss C. Synesthesia D. Phantom vibration syndrome E. PresbyopiaThe gate-control theory proposes that pain signals can be blocked in the:
A. Retina B. Cochlea C. Spinal cord D. Basal ganglia E. HypothalamusSmell and taste are classified together because they both rely on:
A. Mechanoreceptors B. Photoreceptors C. Chemoreceptors D. Thermoreceptors E. Proprioceptors
Answer Key + Quick Rationale
| # | Ans | Why |
|---|---|---|
| 1 | B | Photoreceptors convert light → neural code. |
| 2 | B | Constant proportion (ratio) difference. |
| 3 | B | Hair-cell damage = sensorineural. |
| 4 | C | Afterimage colors are opponent pairs. |
| 5 | C | SDT = sensitivity + decision criterion (motivation). |
| 6 | B | Otolith sacs detect linear acceleration (vestibular). |
| 7 | B | No receptors where axons exit. |
| 8 | A | Mechanical conduction pathway disrupted. |
| 9 | C | Pain “gate” in spinal cord dorsal horn. |
| 10 | C | Both detect chemical molecules. |
Free-Response Practice
FRQ #1 — Weber’s Law in Everyday Life (7 pts)
Question:
Explain Weber’s Law and apply it to (a) adjusting smartphone screen brightness in daylight versus nighttime and (b) a barista adding sugar to small vs. large coffee cups. Include numerical examples and relate to the concept of just-noticeable difference.
Sample High-Scoring Points
Definition (1 pt): JND = constant proportion of original stimulus.
Brightness scenario (2 pts): If threshold ratio is 8 %, a screen at 100 lux must increase by 8 lux in daylight; at 10 lux night room, only 0.8 lux change needed.
Coffee sweetness (2 pts): 8 oz cup needs 1 tsp sugar for detectable change; 16 oz requires ~2 tsp to hit same 8 % sweetness ratio.
Numerical tie-in (1 pt): Show K = ΔI ⁄ I constant.
Link to perception (1 pt): Explains why JND grows with stimulus magnitude.
FRQ #2 — Explaining Two Types of Hearing Loss (7 pts)
Question:
Compare conduction and sensorineural hearing loss in terms of (a) anatomical cause, (b) typical treatment, and (c) one diagnostic test distinguishing them.
High-Scoring Outline
Conduction (3 pts)
Cause: Damage to eardrum/ossicles/oval window.
Treatment: Hearing aids amplify vibration or surgical ossicle replacement.
Test: Rinne test—air vs. bone conduction better via bone.
Sensorineural (3 pts)
Cause: Hair-cell or auditory nerve damage (age, loud noise).
Treatment: Cochlear implant bypasses hair cells → direct nerve stim.
Test: Rinne shows both air & bone poor; otoacoustic emission absent.
Synthesis (1 pt): Only sensorineural helped by cochlear implants because transduction site missing, not conduction path.
Sensation – Quick-Fire Cheat Sheet 🔍⚡️ | AP Psychology online course
| Term / System | Core Fact in 1-Line | Exam Trigger |
|---|---|---|
| Transduction | Receptors convert energy → neural impulses (rods, hair cells, etc.). | “Where does ____ happen?” |
| Absolute Threshold | 50 % detection line (Fechner). | Softest sound, dimmest light Q’s. |
| Difference Threshold (JND) | Constant ratio change (Weber’s Law). | “Detect 2 % change” problems. |
| Sensory Adaptation | Receptor firing ↓ for unchanging stimulus. | “Why don’t you feel your watch?” |
| Signal Detection Theory | Perception = sensitivity + decision bias (hits/false alarms). | Fatigued guard vs. alert guard scenario. |
Vision
Rods = low-light, peripheral. Cones = color, fovea.
Young-Helmholtz (RGB cones) vs. Opponent-Process (R-G ∣ B-Y ∣ B-W afterimages).
Feature detectors in occipital cortex (Hubel & Wiesel).
Hearing
Path: eardrum → ossicles → cochlea/basilar membrane → hair cells.
Place Theory (high pitch @ cochlea base) | Frequency/Volley (low pitch via firing rate).
Conduction loss (middle-ear mechanics) vs Sensorineural loss (hair-cell damage).
Touch & Pain
Receptors → spinal cord → parietal lobe.
Gate-Control Theory: spinal “gate” blocks/lets pain through.
Chemical Senses
Taste buds = sweet, salty, sour, bitter, umami. Regrow ~10 days.
Smell goes straight to limbic, bypasses thalamus → strong emotion memory link.
Body Position
Kinesthesia: tendon/stretch sensors → body-part location.
Vestibular: semicircular canals & otoliths in inner ear → balance & acceleration.
Rapid Mnemonics
“Spare Change?—Weber Ratio!” (JND proportion)
“Opponent Colors Oppose Afterimages.”
“Gate in the Spine, Not the Mind.”
“Rods = Night, Cones = Color.”
Exam Hacks
Blind Spot = optic-nerve exit (no photoreceptors).
Stirrup/oval window damage → conduction hearing loss.
Smell + Taste = chemoreceptors (choose “C”).