Cochlear Map Research Articles

Long-term effects of second cochlear implantation with sequential bilateral cochlear implantation in Japanese children

ObjectiveThis study aimed to longitudinally evaluate speech perception ability and sound-field thresholds with the first, second, or bilateral cochlear implants (CIs) and MAP parameters of second CI in children. MethodsEighteen children who underwent bilateral cochlear implantation at Kyoto University Hospital were included. We evaluated speech perception under quiet and noisy conditions using the first, second, or bilateral CIs, CI-aided sound-field thresholds using the first or second CI, and MAP parameter values (C-levels, T-levels, and dynamic range) of the second CI of more than 5 years after the second implantation. ResultsPatients with a second CI after 7 years of age had significantly worse speech perception ability with the second CI even long after the surgery than those with a second CI before 7 years of age. CI-aided sound-field thresholds using the first or second CI were similar, regardless of the second implantation timing. Speech perception in noise with bilateral CIs was enhanced by the addition of a second CI, even after 7 years of age. Patients undergoing second cochlear implantation before 3.5 years of age showed significantly higher C-levels and wider dynamic ranges in the second CI MAP parameters. ConclusionsWhen the second implantation was performed after 7 years of age, the second CI effects were limited even with long-term use, which is attributed to unstable MAP parameters. The second CI-aided sound-field threshold contributed to the better outcome of bilateral CIs in noise, even if the second implantation was performed at age of ≥7 years.

Altered mapping of sound frequency to cochlear place in ears with endolymphatic hydrops provide insight into the pitch anomaly of diplacusis

A fundamental property of mammalian hearing is the conversion of sound pressure into a frequency-specific place of maximum vibration along the cochlear length, thereby creating a tonotopic map. The tonotopic map makes possible systematic frequency tuning across auditory-nerve fibers, which enables the brain to use pitch to separate sounds from different environmental sources and process the speech and music that connects us to people and the world. Sometimes a tone has a different pitch in the left and right ears, a perceptual anomaly known as diplacusis. Diplacusis has been attributed to a change in the cochlear frequency-place map, but the hypothesized abnormal cochlear map has never been demonstrated. Here we assess cochlear frequency-place maps in guinea-pig ears with experimentally-induced endolymphatic hydrops, a hallmark of Ménière’s disease. Our findings are consistent with the hypothesis that diplacusis is due to an altered cochlear map. Map changes can lead to altered pitch, but the size of the pitch change is also affected by neural synchrony. Our data show that the cochlear frequency-place map is not fixed but can be altered by endolymphatic hydrops. Map changes should be considered in assessing hearing pathologies and treatments.

Research on BatSLAM Algorithm for UAV Based on Audio Perceptual Hash Closed-Loop Detection

This research is aimed at the optimization of a two-dimensional (2D) empirical graph under a certain height and dark conditions for a UAV, using the bionic sonar system to replace the visual sensor’s BatSLAM mode and audio perceptual hash closed-loop detection. The BatSLAM model uses Sum of Absolute Difference (SAD) image processing methods to update the bionic sonar template. This method only judges whether the appearance of the two cochlear images is consistent and does not have geometric processing and feature extraction. Because the cochlear images produce various noises during the acquisition and transmission, there are some differences in cochlear maps obtained at the same position, which can lead to the distortion of the constructed empirical map. In this research, an audio perceptual hash closed-loop detection algorithm is developed to extract features of cochlea. It considers both the appearance and the energy difference between adjacent bands to improve the accuracy of closed-loop detection, thus solving the distortion problem and improving the experience map. The simulation experiment shows that the improved BatSLAM model based on the audio perceptual hash closed-loop detection can improve the 2D experience map for UAV under certain height and dark conditions, through improving the accuracy of the closed-loop detection to solve the distortion problem and thus implementing the optimization of the experience graph.

Cochlear mechanisms underlying the sharp frequency selectivity of hearing

Sharp frequency selectivity, which is a hallmark of mammalian hearing, originates in the cochlea. However, the underlying mechanisms remain unclear. The pioneering work of von Bekesy showed that sounds launch waves of motion along the spiraling basilar membrane, and subsequent hydrodynamic analysis has shown how mechanical properties of the cochlear partition can interact with fluid forces to support sharp frequency tuning. These analyses have generally presumed (or even purported to prove) that longitudinal mechanical coupling through cochlear structures is negligible. Here, we demonstrate that the visco-elastic structure of the tectorial membrane (TM), a gelatinous structure that overlies the sensory receptor cells and plays a key role in stimulating them, also supports traveling waves. The distance over which TM waves propagate provides a measure of mechanical coupling and, through the cochlear map, determines a range of frequencies that correlates strikingly well with direct measurements of cochlear tuning in normal hearing mice, in mice with genetic disorders of hearing, and in humans. These results demonstrate significant longitudinal coupling through the TM and suggest that TM coupling plays an important role in determining the sharpness of cochlear frequency tuning.

The spiral staircase: tonotopic microstructure and cochlear tuning.

Although usually assumed to be smooth and continuous, mammalian cochlear frequency-position maps are predicted to manifest a staircase-like structure comprising plateaus of nearly constant characteristic frequency separated by abrupt discontinuities. The height and width of the stair steps are determined by parameters of cochlear frequency tuning and vary with location in the cochlea. The step height is approximately equal to the bandwidth of the auditory filter (critical band), and the step width matches that of the spatial excitation pattern produced by a low-level pure tone. Stepwise tonotopy is an emergent property arising from wave reflection and interference within the cochlea, the same mechanisms responsible for the microstructure of the hearing threshold. Possible relationships between the microstructure of the cochlear map and the tiered tonotopy observed in the inferior colliculus are explored.

Cochlear Map Boosts Understanding of How Hearing Works

Cochlear Map Boosts Understanding of How Hearing Works

Spatial irregularities of sensitivity along the organ of Corti of the cochlea.

Fine structures of spatial profiles were computed from existing records of cat and chinchilla auditory-nerve fibers on the basis of their characteristic frequencies and cochlear maps. The spatial fine structures of characteristic-frequency thresholds and of "spontaneous" and driven firing rates were mutually correlated, implying the presence of sensitivity fluctuations due to spatial irregularities of presynaptic structures or processes of the inner hair cells and their input. These findings suggest that activity that appears spontaneous is not actually spontaneous and may indicate irregularities of tonotopic mapping in cochlear mechanics.

AN ANTHROPOMORPHIC SPEECH PROCESSING BASED ON THE COCHLEAR MODEL AND ITS APPLICATION FOR CODING TASK

According to antisymmetry of basilar membrane (BM) movements, a new mathematical model of cochlea is derived using viscous cochlear fluid theory, and then transformed into a digital cochlear model with bilinear transformation. The frequency responses are found to be quite consistent with the experimental data, especially the high frequency slope is much more improved. A new cochlear map and 3 dB bandwidth characteristics for cochlear filter banks are obtained and presented, which will make applications of cochlear model more quantitative and accurate. Due to simplicity of its structure and reality of its characteristics, it will be proved the model can be used easily in speech processing system.

Human otoacoustic emissions generated by active outer hair cells

In the present study, human otoacoustic emissions (OAEs) documented in the literature are shown to agree with predictions based on the hypothesis that the main OAE sources are active cochlear outer hair cells (OHCs) of three different functional categories, namely (1) OHCs enabled by oscillating internal organ-of-Corti resonators (IOCRs) to feed mechanical energy into forward-traveling cochlear waves generated by the acoustic stimuli used, (2) OHCs driving spontaneous localized feedback-generated cochlear-partition vibrations involving standing evanescent sound-pressure waves in the liquids above and below the partition, and (3) OHCs causing nonlinear restoring forces enabling pairs of stationary tones to generate distortion products (DPs). The corresponding predictions of OAE properties are based on cochlear maps, i.e., on certain functions x(f), where f is the frequency of a tone and x is a related distance from the cochlear base, measured along the cochlear channel.

Common hearing functions among mammals and birds

Among many mammals and birds, frequency-place cochlear maps have a similar form and differ primarily with respect to the length of the cochlea or basilar papilla, and with respect to the frequency range of hearing. This is remarkable, especially given the differences in anatomical organization and evolutionary history between mammals and birds. This is a striking example of convergent or parallel evolution. With few exceptions, the cochleae of mammals and birds are indeed scale models of one another. One of the primary functions of the frequency-place map is in frequency analysis. Whether this function is defined by frequency discrimination thresholds, critical masking ratios, critical bands or auditory filters in general, frequency analytic performance, behaviorally-defined, can be laid out on the basilar membrane and a critical basilar membrane distance can be associated with a given performance criterion. In general, these critical distances differ according to the function (e.g., frequency delta Fs versus critical bandwidths), but are remarkably similar functions of frequency within and between species (they tend to be constant). It seems likely that evolution has selected the consequences of frequency analytic mechanisms for perception rather than the mechanisms themselves. [Work supported by NIH.]

The spiral model of pitch: Interrelations with musical and psychoacoustic scales and with cochlear parameters

A spiral model of pitch can represent pitch chroma and pitch height. Its arclength provides the frequency-position map of the cochlea, and, when scaled by the number of auditory-ganglion cells, provides the Mel scale. Pitch-like scales fall into three groups. Group I is typified by the Cent scale, which can be expressed as a pitch spiral. Other Group-I scales are musical notation, logarithmic scales of frequency, Fechners Law for complex tones, and the pitch helix. Group II is typified by Greenwoods cochlear map, which is simply related to the arclength of the pitch spiral. Other Group-II scales are the sums of the number of (a) equivalent-rectangular bandwidths (NERBs); (b) difference limens for frequency (NDLFs); and (c) inner-hair cells (NIHCs) and are consistent with critical ratios. Group III is typified by the Mel Scale, which can be derived from the pitch spiral and the distribution of auditory-ganglion cells. Other Group-III scales are the sums of the number of (a) auditory ganglion cells (NSGCs), (b) frequency-modulation-difference limens (NFMDLs), and (c) Barks (NBARKs). The pitch spiral seems a basic concept from which other pitch-like scales can be derived.

Does static ear canal pressure influence pure tone pitch perception?

ObjectiveThat static ear canal air pressure (ECP) influences the frequency of spontaneous otoacoustic emissions (SOAEs) suggests that it may influence intracochlear, in addition to middle ear, processes. A previous study suggested that ECP influences pure tone pitch perception at 1,000 Hz, which was interpreted as indicating an effect on the cochlear place-frequency map. The present study extended investigations of this effect to 500 and 4,000 Hz.Materials and MethodsNine normal-hearing listeners performed interaural pitch matching with monaural ECPs of 0 and -300 daPa.ResultsSome indications of a small downward pitch shift (mean 0.2%) at 500 Hz were observed, which were marginally statistically significant at the 5% level. No pitch shifts were observed at 4,000 Hz.ConclusionsECP does not influence pitch to the extent suggested previously or by SOAE frequency shifts. No evidence was found to support the notion that ECP influences the place-frequency map.

Spiral model of pitch

A spiral model of pitch interrelates tone chroma, tone height, equal temperament scales, and a cochlear map. Donkin suggested in 1870 that the pitch of tones could be well represented by an equiangular spiral. More recently, the cylindrical helix has been popular for representing tone chroma and tone height. Here it is shown that tone chroma, tone height, and cochlear position can be conveniently related to tone frequency via a planar spiral. For this ‘‘equal-temperament spiral,’’ (ET Spiral) tone chroma is conceived as a circular array with semitones at 30° intervals. The frequency of sound on the cent scale (re 16.351 Hz) is represented by the radius of the spiral defined by r=(1200/2π)θr, where θr is in radians. By these definitions, one revolution represents one octave, 1200 cents, 30° represents a semitone, the radius relates θ to cents in accordance with equal temperament (ET) tuning, and the arclength of the spiral matches the mapping of sound frequency to the basilar membrane. Thus, the ET Spiral gives tone chroma as θ, tone height as the cent scale, and the cochlear map as the arclength. The possible implications and directions for further work are discussed.

The mammalian cochlear map is optimally warped.

The form of the mammalian cochlear frequency-position map has been well described by Greenwood and empirical values found for its coefficients for a number of species. The apical portion of the mammalian map is spatially compressed relative to the base, and this nonuniformity in the representation of frequency is evidently consistent across species. However, an evolutionary reason for this consistency, encompassing critical band behavior with respect to position, is conspicuously missing. Likewise, the length of the cochlea in any mammal, including echolocating species, is related to body size, but attempts to explain the length in terms of frequency limits, range, or resolution have no general explanation. New insight stems from a hypothesis in which the map curvature may be appreciated as an adaptation for optimal frequency resolution over the auditory range. It is demonstrated numerically that the mammalian curve may be considered a member of a family of curves which vary in their degree of warp. The "warp factor" found to be common across mammals is an optimal trade-off between four conflicting constraints: (1) enhancing high-frequency resolution; (2) setting a lower bound on loss of existing low-frequency resolution; (3) minimizing map nonuniformity; and (4) keeping the whole map smooth, thereby avoiding reflections.

Evaluating frequency proximity in stream segregation.

Consecutive sounds of similar structure that are close in frequency or pitch are more likely to be perceived as part of the same sequence than those at greater frequency separations. The principle of grouping into such perceptual sequences, or auditory streams, is known as frequency proximity. However, the metric by which one frequency difference is judged to be greater or less than another in complex auditory scenes is not yet known. Two experiments explored the metric for frequency proximity. We presented repeating three-tone stimulus patterns at a rate where they are normally heard as two streams, one containing the highest tone and one containing the lowest. The middle tone joined one stream or the other depending on its frequency. Subjects reported the perceived allocation of the variable tone by responding on a 5-point scale. The frequency at which either of these two percepts was equally probable was found to be lower than a logarithmic midpoint or the midpoints on a cochlear map or the Mel scale; that is, it was unlike metrics arrived at by direct comparisons of tones. Further, the midpoint for high and low tones presented synchronously was lower than that for the same tones presented sequentially, demonstrating that in addition to a proximity factor, some additional factor or factors must operate differently when the lower and upper fixed tones are, or are not, presented simultaneously.

Is the cochlea a wavelet filterbank?

Cochlear place and log-frequency responses are sufficiently similar that frequency-domain measurements are sometimes transformed to place-domain ones, using the cochlear map to relate cochlear place and sinusodial frequency. Such similarity has been attributed to the cochlea’s implementation of a wavelet filterbank. For such a filterbank, place responses at different frequencies are shifted versions of each other, not only for the response magnitude, but also for its phase. According to cochlear macromechanical modeling, however, the cochlear partition velocity at the base leads the stapes velocity by 90 deg, regardless of frequency, which is inconsistent with the place responses at different frequencies being shifted versions of each other. In an alternative formulation, derived from the WKB approximate solution to cochlear dynamic equations, cochlear place and frequency responses are expressed in terms of a prototypical place, not frequency, response. Place responses at different frequencies are scaled shifted versions of the prototype, while frequency responses are derived from the prototype in a more complicated manner. Examples are given for several prototype place response, including a gamma-function envelope with exponential phase.

Rejecting a cochlear-partition model with constant mass

The question of whether a simple low-order, linear, passive model of cochlear-partition dynamics can account for ‘‘global’’ (overall stiffness change, range of best frequencies and best places) and ‘‘local’’ (peakiness of frequency- and place-selectivity, amount of phase-angle change around the best place or frequency) attributes of cochlear response to tones in Békésy’s observations in cadavers remains unresolved. With answering that question the goal, a simple stiffness-damping-mass model of cochlear-partition dynamics with constant mass and exponentially varying stiffness and damping, was investigated computationally using a box-cochlea model of cochlear hydrodynamics. Constrained only by Békésy’s reported change in stiffness by about two orders of magnitude, the model’s global and local response attributes were determined over a reasonably exhaustive set of mechanical parameter values. It was found that the only combinations of mechanical parameters resulting in reasonable cochlear maps had magnitude-response shapes neither qualitatively resembling nor quantitatively consistent with observations by Békésy or anyone else, postmortem or in vivo.

Accurate binaural mirroring of spontaneous otoacoustic emissions suggests influence of time-locking in medial efferents

Spontaneous otoacoustic emissions (SOAEs) of nearly identical acoustic frequency in both ears are a common observation, but it is unknown if this binaural mirroring effect is random, artefactual, genetic, developmental, or of other origin. The available raw data of all human SOAE surveys were pooled, and the intervals of all possible binaural emission pairs ( N=9555) were listed according to size on the Cent-scale (1 Cent=1/100 semitone=1/1200 octave). Statistical analysis showed (1) a slight broad-band mirroring in the 0–100 Cent range ( P<0.05), and (2) a strong narrow-band mirroring (NBM) in the 0–20 Cent range ( P<0.001). Negative results in a detailed SOAE cluster detection program excluded experimental artefacts as causes of NBM. Analysis of the large subgroup of twin data excluded genetic and intrauterine developmental causes. Systemic developmental causes are unrealistic, as 20 Cent corresponds to only ∼80 μm on the cochlear map. Analysis of infant data indicated that the effect may be introduced after birth by secondary factors. Interaural crosstalk was examined but had to be rejected. It is suggested that bilaterally spreading period information in the medial olivocochlear system influences outer hair cells of the same best frequency in both ears very similarly. Evidence concerning possible effects on electromotility is discussed, and experimental tests are proposed.

Cochlear models and minimum phase

In this paper the extent to which the response of a linear cochlear model has the “minimum-phase” property is discussed, along with the topic of what it should mean when experiments confirm or deny the validity of minimum-phase in the response of the actual cochlea. This paper shows that short-wave, long-wave and three-dimensional cochlear models of the “classical” type, in which the operation of the cochlear partition is described by a local function (namely, a driving-point impedance) that produces a cochlear map (from frequency to place), have a response that is minimum-phase, or very close to minimum-phase. Conversely, when the response is found to be non-minimum-phase, the best-fitting model cannot be a classical one.

The Mel Scale's disqualifying bias and a consistency of pitch-difference equisections in 1956 with equal cochlear distances and equal frequency ratios

In 1956, Stevens ‘commissioned’ an experiment to equisect a pitch difference between two tones. Results appear to reveal a methodological flaw that would invalidate the Mel Scale (Stevens and Volkmann, 1940). Stevens sought to distinguish sensory continua, e.g., loudness and pitch, on various criteria. He expected that the pitch continuum would not exhibit ‘hysteresis’; i.e., that subjects dividing a pitch difference (Δf) into equal-appearing parts would not set dividing frequencies higher when listening to notes in ascending order than in descending order. Seven subjects equisected a pitch difference, between tones of 400 and 7000 Hz, into equal-seeming parts by adjusting the frequencies of three intermediate tones. All seven exhibited hysteresis, contrary to expectation. This outcome bears on other issues. Years prior, Stevens suggested that equal pitch differences might correspond to equal cochlear distances, but not to equal frequency ratios nor to equal musical intervals (Stevens and Davis, 1938; Stevens and Volkmann, 1940). In 1960 (reported now), both the 1940 Mel Scale and the equal pitch differences of 1956 were compared to equal cochlear distances, using a frequency-position function that fitted Békésy's cochlear map (Greenwood 1961, 1990). When ascending and descending settings were combined to contra-pose biases, equal pitch differences did coincide with equal distances — which the Mel Scale did not. Further, the biased ascending-order data coincided with the Mel Scale, suggesting the Mel Scale was similarly biased. Thus, the combined-order equal pitch differences of 1956 — but not the Mel Scale — are consistent with equal cochlear distances. However, since the map between 400 and 7000 Hz is nearly logarithmic, equal frequency ratios also approximate equal distances. Ironically, above 400 Hz, Békésy's map and Stevens' equal-distance hypothesis jointly imply that musical intervals will nearly agree with equal pitch differences, which Stevens thought he had disconfirmed. However, given Békésy's map, only near the cochlear apex will equal distances not approximate equal frequency ratios; and Pratt's (Pratt, 1928) bisections of Δfs greater than an octave indicated that equal pitch differences, on average, did agree with equal distances. However, they did so for only two of four subjects and coincided instead with equal frequency ratios for one musical subject. Historical distinctions suggest that between the parts of equisected Δfs subjective equivalence may be of two kinds — one linked to musical intervals, leading to equal frequency ratios; a second linked to ‘tone-height’ and ‘distance’, leading to deviations from equal frequency ratios near the apex, though not appreciably if equisected Δfs are less than an octave (or if perhaps subjects are musicians). Data of other kinds suggest that, if pure-tone pitch height were a function of place, the place could be the apical excitation-pattern edge, in any case not a maximum, which in neural data shifts and disappears with tone level.