Loss Of Frequency Selectivity Research Articles

Stabilizing a Bosonic Qubit Using Colored Dissipation.

Protected qubits such as the 0-π qubit, and bosonic qubits including cat qubits and Gottesman-Kitaev-Preskill (GKP) qubits offer advantages for fault tolerance. Some of these protected qubits (e.g., 0-π qubit and Kerr-cat qubit) are stabilized by Hamiltonians which have (near-)degenerate ground state manifolds with large energy gaps to the excited state manifolds. Without dissipative stabilization mechanisms the performance of such energy-gap-protected qubits can be limited by leakage to excited states. Here, we propose a scheme for dissipatively stabilizing an energy-gap-protected qubit using colored (i.e., frequency-selective) dissipation without inducing errors in the ground state manifold. Concretely we apply our colored dissipation technique to Kerr-cat qubits and propose colored Kerr-cat qubits which are protected by an engineered colored single-photon loss. When applied to the Kerr-cat qubits our scheme significantly suppresses leakage-induced bit-flip errors (which we show are a limiting error mechanism) while only using linear interactions. Beyond the benefits to the Kerr-cat qubit we also show that our frequency-selective loss technique can be applied to a broader class of protected qubits.

Intrinsic AC Shunting in [100]-Tilt Bicrystal YBa2Cu3O $_{7 - x}$ Josephson Junctions

Abstract—[100]-tilt YBa2Cu3O7−x bicrystal Josephson junctions are good candidates to realize high values of characteristic voltages IcRn, which are expected due to large energy gaps in high-Tc materials. Here, we report on detailed electrical characterization of [100]-tilt YBa2Cu3O7−x bicrystal Josephson junctions, which have the maximal IcRn-values up to 9.4 mV, for resistances Rn in the range from 0.9 to 400Ω. The I–V curves have been fitted well to those of the RSJ model with ac-coupled resistive shunts Re. The first derivatives dV/dI versus V have demonstrated a reproducible set of resonances of two types. Numerical simulations of the dV/dI versus V for Josephson junctions coupled with external THz RLC-resonators have been made and both types of resonances have been fitted. A form of the I–V curves and resonances in the first derivatives dV/dI versus V have been attributed to intrinsic broadband and frequency-selective losses, due to interaction of Josephson oscillations with transverse and longitudinal IR-active phonons in YBa2Cu3O7−x electrodes.

Filter characteristics derived from auditory-nerve fiber responses following noise-induced hearing loss.

Sensorineural hearing loss (SNHL) produces a loss of frequency selectivity and elevated thresholds in the auditory periphery. Broadened cochlear tuning significantly affects magnitude and phase responses of auditory filters and thus can change cochlear-response timing. The present study compared auditory-filter characteristics in normal-hearing and noise-exposed anesthetized chinchillas. Impulse responses of auditory filters were derived from responses of auditory-nerve fibers to broadband noise using spike-triggered averaging techniques. Frequency modulations (or frequency glides) in impulse responses were quantified by computing instantaneous frequencies from impulse-response zero crossings. Group delays for individual auditory filters were computed from phase-frequency responses. Cochlear traveling-wave delays were estimated from shuffled cross-correlograms. Preliminary results suggest that auditory-filter best frequency shifts apically following SNHL. Latencies of impulse responses and traveling-wave delays were much shorter following noise exposure. For normal-hearing fibers, frequency glides in impulse responses increased as a function of time for high characteristic-frequency (CF) fibers and decreased for low-CF fibers, consistent with previous studies. SNHL significantly affected frequency glides of noise-exposed fibers in a manner consistent with the loss of tonotopicity. These characterizations of impaired auditory filters have important implications for SNHL effects on temporal and spatiotemporal coding of complex sounds, such as speech. [Work supported by NIH Grant No. R01DC009838.]

Interaction between the motor protein prestin and the transporter protein VAPA

Prestin is the motor protein responsible for cochlear outer hair cell (OHC) somatic electromotility. Eliminating this abundant basolateral membrane protein not only causes loss of frequency selectivity and hearing sensitivity, but also leads to OHC death. A membrane-based yeast two-hybrid approach was used to screen an OHC-enriched cDNA (complementary Deoxyribonucleic Acid) library in order to identify prestin-associated proteins. Several proteins were recognized as potential prestin partners, including vesicle-associated membrane protein associated protein A (VAPA or VAP-33). VAPA is an integral membrane protein that plays an important role in membrane trafficking, endoplasmic reticulum homeostasis, and the stress-signaling system. The connection between VAPA and prestin was confirmed through co-immunoprecipitation experiments. This new finding prompted the investigation of the interaction between VAPA and prestin in outer hair cells. By comparing VAPA expression between wild-type OHCs and OHCs derived from prestin-knockout mice, we found that VAPA is expressed in OHCs and the quantity of VAPA expressed is related to the presence of prestin. In other words, less VAPA protein is found in OHCs lacking prestin. Thus, prestin appears to modify the expression of VAPA protein in OHCs. Intriguingly, more prestin protein appears at the plasma membrane when VAPA is co-expressed with prestin. These data suggest that VAPA could be involved in prestin's transportation inside OHCs and may facilitate the targeting of this abundant OHC protein to the plasma membrane.

Characteristics of Hearing Loss in HDR (Hypoparathyroidism, Sensorineural Deafness, Renal Dysplasia) Syndrome

Haploinsufficiency of the zinc finger transcription factor GATA3 causes the triad of hypoparathyroidism, deafness and renal dysplasia, known by its acronym HDR syndrome. The purpose of the current study was to describe in detail the auditory phenotype in human HDR patients and compare these to audiometrical and histological data previously described in a mouse model of this disease. Pure tone audiometry, speech audiometry, speech in noise, auditory brainstem responses and transiently evoked otoacoustic emissions were measured in 2 patients affected by HDR syndrome. Both patients were affected by a moderate-to-severe sensorineural hearing loss. Speech reception thresholds were shifted and speech recognition in noise was disturbed. No otoacoustic emissions could be generated in either patient. Auditory brainstem response interpeak intervals were normal. The human and murine audiological phenotypes seem to correspond well. Hearing loss in HDR syndrome is moderate to severe, seems to be slightly worse at the higher end of the frequency spectrum and may be progressive with age. The absence of otoacoustic emissions and the loss of frequency selectivity suggest an important role for outer hair cells in causing the hearing loss.

Recent developments in signal processing for digital hearing aids

pproaches in signal processing research on digital hearing aids fall into four areas, which cover signal acquisition, amplification, transmission, measurement, filtering, parameter estimation, separation, detection, enhancement, modeling, and classification. The first area uses advanced signal processing techniques to characterize and compensate for various hearing impairments such as loudness and frequency selectivity loss. The second area consists of effective target signal enhancement and noise reduction, which includes adaptive microphone array technologies, spectral

Fundamental frequency discrimination and harmonic resolvability in sensorineural hearing impariment

Sensorineural hearing loss (SNHL) often results in impaired fundamental frequency (F0) processing. Three experiments tested the hypothesis that this deficit is related to a loss of frequency selectivity, which may result in fewer peripherally resolved harmonics. F0 difference limens (F0DLs) were measured as a function of F0 for bandpass filtered sine- and random-phase harmonic complexes in listeners with mild-to-moderate SNHL. All listeners showed a transition between small (good) F0DLs at high F0s and large (poor) F0DLs at low F0s, although the transition point varied across subjects. Two measures that are thought to reflect frequency selectivity generally corresponded to the F0DL transition point: the maximum F0 for which F0DLs were phase-dependent, and the minimum modulation frequency required to discriminate amplitude modulation from quasi-frequency modulation. These results provide some support for the idea that the F0-processing deficit associated with SNHL is related to poor frequency selectivity. However, contrary to our hypothesis, poor correspondence was observed between the F0DL transition point and auditory filter bandwidths estimated using the notched-noise method in the same subjects. This suggests a possible discrepancy between traditional spectral-masking estimates of frequency selectivity and estimates based on temporal interactions between unresolved components. [Work supported by NIH grants R01DC05216 and 5T32DC00038.]

A speech enhancement scheme incorporating spectral expansion evaluated with simulated loss of frequency selectivity.

Hearing-impaired listeners often suffer from supra-threshold speech perception deficits. One such deficit is reduced frequency selectivity. We applied a speech enhancement scheme that incorporated spectral expansion in an attempt to reduce the effects of this deficit. The speech processing could contain up to three stages, a first in which the peak-valley ratio of the speech spectrum was enlarged to counteract the broadening of the auditory filtering, and a second in which the overall speech spectrum was modified to counteract the effects of upward-spread-of-masking, using a linear filter. The third stage was a noise suppression stage, applied before the spectral enhancement. The effectiveness of the speech processing with and without noise suppression was evaluated for various parameter settings by measuring the speech reception threshold (SRT) in noise, i.e., the signal-to-noise ratio at which listeners repeat 50% of presented sentences correctly. We used normal-hearing subjects. To simulate the loss of frequency selectivity we applied spectral smearing to the stimuli presented to the subjects. The speech material of the SRT tests was mixed with the noise before processing, and, when present, the smearing was applied last. The results indicated that for one specific parameter setting the SRT values decreased (i.e., improved) by approximately 1 dB when incorporating the spectral expansion together with the linear filtering. Employing either of these two stages separately did not improve the SRT. The application of the noise suppression stage did not further improve the SRT. A pilot study using hearing-impaired listeners showed more promising results for a female than for a male speaker.

A scheme for noise suppression and spectral enhancement of speech to alleviate speech reception problems from loss of frequency selectivity

Even after sufficient amplification, hearing-impaired listeners often experience problems in understanding speech under noisy conditions. This may be caused by suprathreshold deficits such as loss of compression and reduced frequency selectivity. In this project we investigate a scheme in which speech and noise are processed before presentation to try and alleviate intelligibility problems caused by reduced frequency selectivity. The scheme contains three strategies, one in which the peak-to-valley ratios of selected modulations in the speech spectrum are enlarged, a second in which the overall speech spectrum is modified, and a third in which noise is suppressed before the two enhancement steps. An overlap-and-add (OLA) algorithm is used in the implementation. The effect of the speech processing is evaluated by measuring speech-reception thresholds (SRT) for sentences in speech noise, estimating the signal-to-noise ratio at which listeners can correctly reproduce 50% of presented sentences. Hearing-impaired and normal-hearing listeners were used. To simulate the hearing impairment resulting from a loss of frequency selectivity, we spectrally smeared the stimuli presented to the normal-hearing listeners. We found that the preprocessing scheme achieved a modest improvement of nearly 2 dB in the SRT for normal-hearing listeners. Data for hearing-impaired listeners are presently being collected.

Auditory filter nonlinearity in mild/moderate hearing impairment.

Sensorineural hearing loss has frequently been shown to result in a loss of frequency selectivity. Less is known about its effects on the level dependence of selectivity that is so prominent a feature of normal hearing. The aim of the present study is to characterize such changes in nonlinearity as manifested in the auditory filter shapes of listeners with mild/moderate hearing impairment. Notched-noise masked thresholds at 2 kHz were measured over a range of stimulus levels in hearing-impaired listeners with losses of 20-50 dB. Growth-of-masking functions for different notch widths are more parallel for hearing-impaired than for normal-hearing listeners, indicating a more linear filter. Level-dependent filter shapes estimated from the data show relatively little change in shape across level. The loss of nonlinearity is also evident in the input/output functions derived from the fitted filter shapes. Reductions in nonlinearity are clearly evident even in a listener with only 20-dB hearing loss.

Further evaluation of a model of loudness perception applied to cochlear hearing loss.

This paper describes further tests of a model for loudness perception in people with cochlear hearing loss. It is assumed that the hearing loss (the elevation in absolute threshold) at each audiometric frequency can be partitioned into a loss due to damage to outer hair cells (OHCs) and a loss due to damage to inner hair cells (IHCs) and/or neurons. The former affects primarily the active mechanism that amplifies the basilar membrane (BM) response to weak sounds. It is modeled by increasing the excitation level required for threshold, which results in a steeper growth of specific loudness with increasing excitation level. Loss of frequency selectivity, which results in broader excitation patterns, is also assumed to be directly related to the OHC loss. IHC damage is modeled by an attenuation of the calculated excitation level at each frequency. The model also allows for the possibility of complete loss of IHCs or functional neurons at certain places within the cochlea ("dead" regions). The parameters of the model (OHC loss at each audiometric frequency, plus frequency limits of the dead regions) were determined for three subjects with unilateral cochlear hearing loss, using data on loudness matches between sinusoids presented alternately to their two ears. Further experiments used bands of noise that were either 1-equivalent rectangular bandwidth (ERB) wide or 6-ERBs wide, centered at 1 kHz. Subjects made loudness matches for these bands of noise both within ears and across ears. The model was reasonably accurate in predicting the results of these matches without any further adjustment of the parameters.

Hearing recovery in neonatal chicks after exposure to intense pure tones

Neonatal chicks exposed to a 120-dB SPL pure tone at 0.9 kHz for 48 to 200 h exhibited a severe loss in auditory function. The growth and recovery of hearing loss was traced with a variety of peripheral evoked-potential and single-cell recordings. The growth of threshold shift and the loss of frequency selectivity reached asymptotic levels after 40 h and then remained constant to 200 h. At 0 days of recovery the magnitude of threshold shift in the most affected frequencies was 55–60 dB and tuning curves showed a 50% loss in selectivity. Nearly complete recovery of sensitivity and selectivity was noted 12–15 days post exposure. Severe recruitment was also seen in functions relating sound level to evoked-potential amplitude or single cell rate-intensity functions. The abnormal coding of intensity returned to normal within 3 days. The loss in function was associated with significant cochlear damage, and recovery was associated with considerable cochlear repair. The repaired cochlea, however, does not have a normal appearance. It remains to be explained how auditory function can completely recover in a cochlea with severe permanent structural defects. [Work supported by the NIDCD, PLHRF, and NOAR.]

Validation of a computerized auditory model for the analysis of warning sounds.

A computerized model was developed to predict the detectability of warning sounds in noisy workplaces. A previous study with 23 subjects having different degrees of noise-induced hearing loss allowed to quantify the relation between loss of auditory sensitivity and loss of frequency selectivity. This relation was then introduced into the model. This model takes into account the loss of auditory sensitivity and selectivity due to cochlear hearing loss and the use of hearing protectors. It is based essentially on loudness summation and excitation patterns. Before making the program available to health and safety personnel, a field study is being conducted in order to validate its predictions in terms of signal detection and recognition. The perception of three different warning sounds with well-defined acoustic characteristics (a buzzer, a siren, and a horn) is studied with different background noises from a steel and a bottling plant. At five different workstations, workers are asked to raise their hand when they hear a warning sound emitted by a loudspeaker. The time interval between two warning sounds varies between 10 and 50 s (an average of 30 s). The sound level is randomly set to one of five levels corresponding to S/N ratios between −5 and +15 dB within a 1/3 octave band. Based on previous studies, it is suspected that a signal-to-noise ratio of +15 dB is needed in at least 1/3 octave band in order (1) that the warning signal be detected, (2) that it attracts the attention of the workers, and (3) that it be recognized among other warning sounds. Results will be discussed with respect to the safety of workers in noisy workplaces. [Work supported by IRSST.]

Frequency selectivity and psychoacoustic tuning curves in old age

Frequency selectivity represents an important contributory factor in the understanding of human speech. It refers to the ability of the ear to discriminate between two simultaneously occurring sounds of different spectral composition. The capabilities of frequency selection, time pattern analysis, and information processing can be determined generally only by speech audiometry. Schorn and co-workers (1977) published a simplified method for audiological investigations whereby results obtained at two different frequency values are sufficient. The test tone frequencies of 0.5 and 4 kHz were selected because they are representative of the frequency range of normal speech. To determine the influence of ageing on frequency selectivity we investigated three groups of patients between the ages of 20-30, 40-50 and 60-70 years. All of the subjects had normal hearing according to ISO 7029 standards. The measurements of pure-tone audiometry, speech audiometry, and the psychoacoustic tuning curves were performed sequentially on the same day. The influence of ageing on frequency selectivity mainly concerns frequencies above 2 kHz. This is related to the progressive loss of outer hair cells in the basal parts of the cochlea in old age. Our investigations show that particular attention must be paid to a loss of frequency selectivity in old age. This becomes evident mainly after the 60th year. Frequency selectivity is not significantly disturbed before that age, although pure tone audiograms show high frequency inner ear hearing loss earlier in life.

Spatial frequency-selective losses with pattern electroretinogram in Type 1 (insulin-dependent) diabetic patients without retinopathy

Neurosensory abnormalities have been implicated in the first stages of diabetic retinopathy. The activity of retinal ganglion cells in 24 Type 1 (insulin-dependent) diabetic patients with short disease duration without retinopathy on fluorescein angiography was investigated by using a pattern electroretinogram in response to sinusoidal gratings of different spatial frequencies (0.6, 1.0, 1.4, 2.2 4.8 cycles/deg), counterphase modulated at 8 Hz. The pattern electroretinogram reflects, at least in part, the activity of subsets of generators (i.e. ganglion cells) which show spatial selectivity. Mean pattern electroretinogram amplitude was significantly reduced in patients at lower and intermediate, but not at higher spatial frequencies compared with 40 age-matched control subjects. At 1.4 cycles/deg the pattern electroretinogram amplitude was significantly correlated (r = 0.59) with age at onset (p = 0.002) and duration of disease (p = 0.002). Our results suggest that in Type 1 diabetic patients without retinopathy, there is an early sensory deficit of specific inner retina neurons which respond preferentially to gratings of medium and large size.

Breakdown of the sequence of active transitions in a waveguide CO2laser with a selective resonator

Breakdown of the sequence of active transitions in a waveguide CO2 laser occurred as a result of a change in the angle of inclination of a diffraction grating. This was accompanied by a change in the transverse distribution of the laser radiation intensity and was manifested at low rotational quantum numbers J. The observed effect was due to the characteristics of the frequency-selective losses in the selective waveguide resonator.

The Psychoacoustics of Profound Hearing Impairment.

A group of profoundly hearing-impaired adults is being studied in order to determine their residual auditory capabilities. Most tests use acoustic contrasts that have relevance for the perception of speech, so that the results obtained may be used to guide the development of appropriate hearing aids. All the listeners are postlingually deafened, with losses >95 dB HL at and above 500 Hz, and least loss at low frequencies. Trends in detection thresholds, discomfort levels, dynamic ranges, intensity discrimination (both static and dynamic), frequency selectivity, spectral shape discrimination, gap detection, tone/noise discrimination, frequency discrimination and phase sensitivity are reported and discussed. Generally speaking, temporal resolving power seems to be more resistant to degradation than mechanisms of frequency selectivity. Furthermore, at least some of the differences in performance between normal and profoundly-impaired listeners may be attributable to the loss of frequency selectivity. Implications are drawn for hearing aid fitting and design, and comparisons made to the electro-auditory abilities of users of single-channel cochlear implants.

Selective properties of gas-laser resonators containing a planar waveguide

A calculation is reported of selective and nonselective losses in a resonator containing a planar waveguide and reflectors located near the waveguide ends. The conditions resulting in degeneracy of the resonator modes are determined. An analysis is made of the influence of geometric and optical parameters of the waveguide, and of the waveguide–mirror distance on the frequency-selective losses in such a waveguide resonator. The results obtained are compared with corresponding results for resonators containing waveguides of different geometry.

Spatial contrast sensitivity in unilateral cerebral ischaemic lesions involving the posterior visual pathway.

Contrast sensitivity function was studied in 16 patients with unilateral ischaemic lesions involving the posterior visual pathway. Sixty-two percent of the patients showed contrast sensitivity loss in at least one eye for horizontal or vertical stimulus orientation. Visual perception was distorted in a qualitatively different way according to the anteroposterior site of the lesion. Patients with occipital or occipitotemporal lesions showed high spatial frequency selective losses and patients with temporal or parietal lesions low frequency selective losses. Stimulus orientation selectivity was observed in patients with lesions of the primary visual cortex as well as in patients with lesions anterior to the striate cortex. Contrast sensitivity orientation-selective losses were demonstrated in 14 of the 17 'affected' eyes.

Acoustically induced hearing loss: Intracellular studies in the guinea pig cochlea

Intracellular recordings were made from both inner and outer hair cells (IHC, OHC) in the basal coil of the guinea pig cochlea before, during and after the animal was exposed to loud, pure tones. Following multiple loud tones both types of sensory cells demonstrate a culmulative decrease in their voltage responses to a test tone. A loss in sensitivity of the compound action potential (CAP) of the eighth nerve co-incides with a decrease in both the amplitude of the IHC receptor potential and the positive summating potential (+SP) recorded at the round window. The largest decreases in sensitivity of IHCs are found at the characteristic or best frequency (CF) of each cell and this frequency selective loss of sensitivity results in a decrease in the tuning of the hair cell. During and following a loud tone the nonlinear properties of IHCs are also reduced.