Comprehensive Sound Waves and Auditory System: Physics, Neurobiology, and Speech

*Q:* What are sound waves?

*A:* Oscillations of air pressure that propagate outward as alternating regions of compression and rarefaction.

*Q:* How are pressure waves transduced into perception?

*A:* They are converted into neural signals that the brain interprets as pitch (frequency) and loudness (amplitude).

*Q:* What physical property of sound corresponds to pitch?

*A:* Frequency (measured in Hz).

*Q:* What physical property of sound corresponds to loudness?

*A:* Amplitude (measured in dB).

*Q:* What does waveform determine?

*A:* The timbre or sound quality.

*Q:* How does sound travel through air?

*A:* By compression and rarefaction of air molecules, creating pressure waves.

*Q:* Where are high vs. low frequencies transduced in the cochlea?

*A:* High frequencies = base (stiff), low frequencies = apex (flexible).

*Q:* What is tonotopic organization?

*A:* Spatial mapping of frequencies along the basilar membrane.

*Q:* What do inner hair cells do?

*A:* Convert vibrations into neural signals.

*Q:* What do outer hair cells do?

*A:* Amplify and sharpen responses (cochlear amplifier).

*Q:* What does the tectorial membrane do?

*A:* Interacts with stereocilia during vibration.

*Q:* What opens when stereocilia bend?

*A:* Mechanically gated TRPa1 ion channels.

*Q:* Which ion drives depolarization in hair cells?

*A:* Potassium (K+) from the endolymph.

*Q:* What maintains ionic separation in the cochlea?

*A:* The reticular lamina.

*Q:* Which fluid is high in K+?

*A:* Endolymph.

*Q:* Which fluid is high in Na+?

*A:* Perilymph.

*Q:* What is electromotility?

*A:* OHCs change length in response to electrical stimulation, amplifying sound.

*Q:* Which neurotransmitter regulates OHCs?

*A:* Acetylcholine (via efferent fibers).

*Q:* What are characteristic frequencies?

*A:* Frequencies to which auditory nerve fibers respond most sensitively.

*Q:* What is phase locking?

* A:* Neurons firing in sync with sound wave phases, enabling high-frequency coding.

*Q:* How do cochlear implants mimic hearing?

*A:* By electrically stimulating auditory nerve regions in tonotopic order.

*Q:* What is a fundamental frequency?

*A:* The lowest and most prominent pitch in a sound.

*Q:* What are overtones/harmonics?

*A:* Higher frequency components shaping timbre.

*Q:* Difference between morphemes and phonemes?

*A:* Morphemes = smallest meaning units; Phonemes = smallest sound units distinguishing meaning.

*Q:* What is the mental lexicon?

*A:* The brain's store of semantic, syntactic, and form knowledge about words.

*Q:* Do chimpanzees have language?

*A:* No—only symbolic communication without human-like syntax or complexity.

*Q:* Broca's area function?

*A:* Speech production (motor).

*Q:* Wernicke's area function?

*A:* Language comprehension.

*Q:* What connects Broca's and Wernicke's areas?

*A:* The arcuate fasciculus.

*Q:* Broca's aphasia vs. Wernicke's aphasia?

*A:* Broca's = nonfluent, effortful speech but good comprehension.

Wernicke's = fluent but nonsensical speech, poor comprehension.

*Q:* What is conduction aphasia?

*A:* Damage to arcuate fasciculus, impairing repetition.

*Q:* Which hemisphere is dominant for speech?

*A:* Left hemisphere.

*Q:* What is the right-ear advantage?

*A:* Speech sounds are processed better by the right ear → left hemisphere.

*Q:* Which hemisphere is stronger in pitch perception?

*A:* Right hemisphere.

*Q:* What is alexia?

*A:* Inability to read due to angular gyrus lesions.

*Q:* What is auditory agnosia?

*A:* Inability to recognize sounds despite normal hearing thresholds.

*Q:* What cues help localize sound?

*A:* Interaural time difference (ITD) and interaural level difference (ILD).

*Q:* Which frequencies use ITD vs ILD?

*A:* ITD = low frequencies; ILD = high frequencies.

*Q:* What is the acoustic shadow?

*A:* Head blocking high-frequency sounds, creating intensity differences.

*Q:* How does the pinna aid localization?

*A:* Provides spectral cues for elevation and front-back discrimination.

*Q:* What is auditory scene analysis?

*A:* Grouping sounds by harmonic coherence, aided by top-down corticofugal input.

*Q:* What is perceptual completion?

*A:* Brain filling in gaps when sounds are interrupted.

*Q:* Which animals use ultrasonic hearing?

*A:* Bats (180k Hz), dolphins (130k Hz), crickets (15k+ Hz).

*Q:* How do bats use echolocation?

*A:* Ultrasonic clicks/chirps, analyzing returning echoes with coincidence detectors.