Hearing

Detection and processing of acoustic stimulation. Signal detectability depends on the receiver and background noise.

Auditory feedback is information obtained by hearing the sound produced by one's own action. During vocal control, it can be compared with an intended or learned sound, allowing later production to be adjusted. Hearing another individual's demonstration supplies an example to learn; hearing the consequences of one's own production supplies feedback. The two experiences have different causal roles.

A controlled birdsong experiment manipulated that distinction. Adult Bengalese finches wore custom headphones; a cage microphone fed sound-processing hardware that shifted the pitch of their own songs before playback. The birds changed their produced pitch in the compensatory direction, and pitch returned toward baseline when the perturbation was removed. Stable adult song therefore remained subject to active correction under these conditions.^[ref]

For an original numerical illustration, a playback system that multiplies frequency by $2^{1/12}$ turns a $500$-hertz component into about $529.7$ hertz. To cancel that multiplicative shift exactly, production would need to be about $500/2^{1/12}=471.9$ hertz. These values illustrate the direction of an ideal compensation, not a claim that the birds achieved complete correction.

Altered auditory feedback can thus probe a control mechanism without simply disabling hearing. Timing, pitch and loudness are distinct perturbations, and a response to one manipulation does not establish identical control rules for every species or vocal behavior.

Audiometry measures aspects of hearing under specified stimulus and response conditions. A tone-detection threshold depends on frequency, presentation route and the task. It is a psychophysical measurement rather than a complete description of every auditory ability.

Measurement of the mechanical response of the tympanic membrane and middle ear as ear-canal pressure changes.

The cochlear nerve fibres carrying auditory information from hair cells toward the brain.

Perception of a speech sequence as containing a segment whose acoustic information has been replaced by another sound. The classic contrast with a silent gap shows the importance of the replacement sound as plausible masking evidence. The perceived continuity does not mean that the missing waveform has been reconstructed from the ear signal alone.^[ref]

Processes that organize a mixture of sound into perceptual streams and auditory objects. They must balance grouping evidence against the need to separate overlapping sources and update representations as events change.

A direction-dependent acoustic transfer function from an external source to one ear, including effects of the head, pinna and torso under stated measurement conditions. Individual geometry changes the spectral cues. A pair of such functions predicts binaural signals for a known source; inferring direction from unknown sounds is a harder inverse problem.

A difference in sound level between the ears, often influenced by the head's direction- and frequency-dependent acoustic shadow. It complements interaural time differences, rather than serving as an exact independent direction label in every environment.

The difference in arrival time or corresponding temporal structure of sound at the two ears. In an ideal far-field point-receiver model with separation $d$, $\Delta t=d\sin \theta /c$ follows from the path difference divided by sound speed. Head diffraction, multiple sources and reverberation complicate this approximation; one delay need not identify a unique direction.

Sound qualities supporting distinctions between sources beyond overall level, duration and pitch. Spectral shape, temporal envelopes and their changes contribute; no single scalar need describe every timbral difference.

A perceptual attribute allowing sounds to be ordered as relatively high or low. It is related to, but not identical with, acoustic frequency or the location of the largest component in a frequency spectrum. Complex periodic signals require consideration of temporal and spectral structure.

An orderly relation between preferred acoustic frequency and anatomical position in a sensory structure. Cochlear mechanical tonotopy originates in graded mechanics, while later tonotopic neural organization involves additional processing. A frequency map is not itself a complete sound-object representation.

The fluid-filled inner-ear structure whose graded mechanics and sensory cells transform sound-driven vibration into neural signals. Distributed frequency selectivity, active feedback and temporal coding contribute distinct information; a cochlear place response alone does not identify the physical source of a sound.

The sensory apparatus supported by the basilar membrane and containing cochlear hair cells. Their mechanotransduction helps convert vibration into auditory signals.

Active biological feedback contributing level-dependent gain and frequency tuning to cochlear mechanics. It can enhance weak near-characteristic-frequency stimulation more than intense or off-frequency stimulation. A perturbation of the whole preparation must be interpreted carefully because it can alter both mechanical and neural transduction processes.

A sensory cell whose mechanically sensitive bundle supports mechanotransduction. The cochlear inner and outer classes have different dominant roles in afferent signaling and mechanical feedback.

A cochlear hair-cell class contributing mechanical feedback that increases weak-sound sensitivity and sharpens frequency selectivity. Its feedback-dependent effects are part of the cochlear amplifier.

A cochlear hair-cell class providing most afferent input to the auditory nerve. Mechanical stimulation changes receptor activity and transmitter release; downstream auditory nerve fibers carry action potentials.

A mechanically graded structure supporting frequency-dependent traveling-wave responses in the cochlea. High-frequency responses peak nearer the base and low-frequency responses nearer the apex. Its living response is modified by the cochlear amplifier, so passive mechanical measurements do not capture the entire operating system.

The tympanic membrane and ossicular coupling system that transfers airborne vibration toward the fluid-filled inner ear. Its mechanical transformation helps address an acoustic impedance mismatch; it is not an ideal, lossless, frequency-independent amplifier.

The tensor tympani muscle is a middle-ear muscle attaching to the malleus. Its contraction alters the mechanics of the tympanic membrane and ossicular chain. Its innervation is associated with the mandibular division of the trigeminal nerve, rather than the facial supply to stapedius.

The tubotympanic recess is an embryonic extension of the first pharyngeal pouch contributing to the auditory tube and middle-ear cavity. Its endodermal origin differs from the ectodermal contribution to the external ear passage.

The tympanic cavity is the air-containing middle-ear space housing the auditory ossicles. It communicates with the nasopharynx through the auditory tube. The cavity, its lining and the structures suspended within it have different mechanical and developmental roles.

The Eustachian tube connects the middle ear to the nasopharynx, enabling pressure equalization, mucosal clearance and protection from nasopharyngeal contents.

Interference with detection or discrimination of a sound by other sounds. Signal frequency, amplitude, timing and receiver processing can affect masking.

Interference involving uncertainty, source confusion or selection beyond a simple account of overlapping acoustic energy. Demonstrating it requires suitable controls for audibility and peripheral overlap; merely finding a difficult listening task is insufficient.

Reduced target detectability associated with overlap between target and interfering acoustic energy in the listener's representation. It is distinguished conceptually from informational masking, although both can occur in one task and the distinction does not identify one anatomical site automatically.