Spectral integration of speech bands in normal-hearing and hearing-impaired listeners

This investigation examined whether listeners with mild-moderate sensorineural hearing impairment have a deficit in the ability to integrate synchronous spectral information in the perception of speech. In stage 1, the bandwidth of filtered speech centered either on 500 or 2500 Hz was varied adaptively to determine the width required for approximately 15%-25% correct recognition. In stage 2, these criterion bandwidths were presented simultaneously and percent correct performance was determined in fixed block trials. Experiment 1 tested normal-hearing listeners in quiet and in masking noise. The main findings were (1) there was no correlation between the criterion bandwidths at 500 and 2500 Hz; (2) listeners achieved a high percent correct in stage 2 (approximately 80%); and (3) performance in quiet and noise was similar. Experiment 2 tested listeners with mild-moderate sensorineural hearing impairment. The main findings were (1) the impaired listeners showed high variability in stage 1, with some listeners requiring narrower and others requiring wider bandwidths than normal, and (2) hearing-impaired listeners achieved percent correct performance in stage 2 that was comparable to normal. The results indicate that listeners with mild-moderate sensorineural hearing loss do not have an essential deficit in the ability to integrate across-frequency speech information.     

Effects of acoustic modification on consonant recognition by elderly hearing-impaired subjects

In a recent study [S. Gordon-Salant, J. Acoust. Soc. Am. 80, 1599-1607 (1986)], young and elderly normal-hearing listeners demonstrated significant improvements in consonant-vowel (CV) recognition with acoustic modification of the speech signal incorporating increments in the consonant-vowel ratio (CVR). Acoustic modification of consonant duration failed to enhance performance. The present study investigated whether consonant recognition deficits of elderly hearing-impaired listeners would be reduced by these acoustic modifications, as well as by increases in speech level. Performance of elderly hearing-impaired listeners with gradually sloping and sharply sloping sensorineural hearing losses was compared to performance of elderly normal-threshold listeners (reported previously) for recognition of a variety of nonsense syllable stimuli. These stimuli included unmodified CVs, CVs with increases in CVR, CVs with increases in consonant duration, and CVs with increases in both CVR and consonant duration. Stimuli were presented at each of two speech levels with a background of noise. Results obtained from the hearing-impaired listeners agreed with those observed previously from normal-hearing listeners. Differences in performance between the three subject groups as a function of level were observed also.     

The role of time and place cues in the detection of frequency modulation by hearing-impaired listeners

Frequency modulation detection limens (FMDLs) were measured for five hearing-impaired (HI) subjects for carrier frequencies f(c) = 1000, 4000, and 6000 Hz, using modulation frequencies f(m) = 2 and 10 Hz and levels of 20 dB sensation level and 90 dB SPL. FMDLs were smaller for f(m) = 10 than for f(m) = 2 Hz for the two higher f(c), but not for f(c) = 1000 Hz. FMDLs were also determined with additional random amplitude modulation (AM), to disrupt excitation-pattern cues. The disruptive effect was larger for f(m) = 10 than for f(m) = 2 Hz. The smallest disruption occurred for f(m) = 2 Hz and f(c) = 1000 Hz. AM detection thresholds for normal-hearing and HI subjects were measured for the same f(c) and f(m) values. Performance was better for the HI subjects for both f(m). AM detection was much better for f(m) = 10 than for f(m) = 2 Hz. Additional tests showed that most HI subjects could discriminate temporal fine structure (TFS) at 800 Hz. The results are consistent with the idea that, for f(m) = 2 Hz and f(c) = 1000 Hz, frequency modulation (FM) detection was partly based on the use of TFS information. For higher carrier frequencies and for all carrier frequencies with f(m) = 10 Hz, FM detection was probably based on place cues.     

The principle of acoustic time reversal and holography

On the basis of earlier results (V. A. Zverev, Radiooptics (1975)), the principle of the time reversal of waves (TRW) with the use of a time-reversed signal is considered (M. Fink et al., Time-Reversed Acoustics, Rep. Prog. Phys. 63 (2000)). Both the common mathematical basis and the difference between the TRW and holography are revealed. The following conclusions are drawn: (i) to implement the TRW, it is necessary that the spatial and time coordinates be separated in the initial signal; (ii) two methods of implementing the TRW are possible, namely, the time reversal and the use of an inverse filter; (iii) certain differences exist in the spatial focusing by the TRW and holography; and (iv) on the basis of the theory developed, a numerical modeling of the TRW becomes possible.     

The linear acceleration time integration method revisited

An unconditionally stable “two-node” finite element in time is proposed that can be used to integrate numerically the semidiscretized equations of motion of a continuous body. In analogy to the popular “linear acceleration” scheme [1,2], the proposed procedure may be termed a “linear displacement” algorithm for it is based on linear approximations of the displacement vector, x, within each time interval. On the basis of a rigorous mathematical analysis, it is shown that the algorithmic characteristics (i.e., accuracy, computational effort, etc.) are identical with those of the linear acceleration procedure. The advantages of the proposed technique over the assumed acceleration method [3] become evident in the case of higher order one-step time integration algorithms.     

The incubation time criterion and the acoustic strength of sea water

The approach based on the incubation time concept is used to analyze experimental data on acoustic cavitation in degassed water and in sea water. Earlier, a similar approach proved to be effective in analyzing the cavitation due to pulse loading and in studying the dynamic strength of solids. The proposed criterion takes into account the existence of the static cavitation threshold for low-frequency loading and makes it possible to explain the growth of the cavitation threshold for high-frequency loading, as well as the appreciable spread in experimental data.     

Phonetic training with acoustic cue manipulations: a comparison of methods for teaching English /r/-/l/ to Japanese adults

Recent work [Iverson et al. (2003) Cognition, 87, B47-57] has suggested that Japanese adults have difficulty learning English /r/ and /l/ because they are overly sensitive to acoustic cues that are not reliable for /r/-/l/ categorization (e.g., F2 frequency). This study investigated whether cue weightings are altered by auditory training, and compared the effectiveness of different training techniques. Separate groups of subjects received High Variability Phonetic Training (natural words from multiple talkers), and 3 techniques in which the natural recordings were altered via signal processing (All Enhancement, with F3 contrast maximized and closure duration lengthened; Perceptual Fading, with F3 enhancement reduced during training; and Secondary Cue Variability, with variation in F2 and durations increased during training). The results demonstrated that all of the training techniques improved /r/-/l/ identification by Japanese listeners, but there were no differences between the techniques. Training also altered the use of secondary acoustic cues; listeners became biased to identify stimuli as English /l/ when the cues made them similar to the Japanese /r/ category, and reduced their use of secondary acoustic cues for stimuli that were dissimilar to Japanese /r/. The results suggest that both category assimilation and perceptual interference affect English /r/ and /l/ acquisition.     

The perception of phonemic contrasts in a non-native dialect

This study examined the impact on speech processing of regional phonetic/phonological variation in the listener's native language. The perception of the /e/-/epsilon/ and /o/-/upside down c/ contrasts, produced by standard but not southern French native speakers, was investigated in these two populations. A repetition priming experiment showed that the latter but not the former perceived words such as /epe/ and /epepsilon/ as homophones. In contrast, both groups perceived the two words of /o/-/upside down c/ minimal pairs (/pom/-/p(uspide down c)m/) as being distinct. Thus, standard-French words can be perceived differently depending on the listener's regional accent.     

Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time

The increasing presence of low frequency sources and the lack of acoustic standard measurement procedures make the extension of reverberation time measurements to frequencies below 100 Hz necessary. In typical ordinary rooms with volumes between 30 m³ and 200 m³ the sound field is non-diffuse at such low frequencies, entailing inhomogeneities in space and frequency domains. Presence of standing waves is also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays caused by room modes, a new approach based on reverberation time measurements of single resonant frequencies (the modal reverberation time) has been introduced. From background theory, due to the intrinsic relation between modal decays and half bandwidth of resonant frequencies, two measurement methods have been proposed together with proper measurement procedures: a direct method based on interrupted source signal method, and an indirect method based on half bandwidth measurements. With microphones placed at corners of rectangular rooms in order to detect all modes and maximize SNRs, different source signals were tested. Anti-resonant sine waves and sweep signal turned out to be the most suitable for direct and indirect measurement methods respectively. From spatial measurements in an empty rectangular test room, comparison between direct and indirect methods showed good and significant agreements. This is the first experimental validation of the relation between resonant half bandwidth and modal reverberation time. Furthermore, comparisons between means and standard deviations of modal reverberation times and standard reverberation times in third octave bands confirm the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach. Modal reverberation time measurements applied to furnished ordinary rooms confirm previous results in the limit of modal sound field: for highly damped modes due to furniture or acoustic treatment, the indirect method is not applicable due to strong suppression of modes and the consequent deviation of the acoustic field from a non-diffuse condition to a damped modal condition, while standard reverberation times align with direct method values. In the future, further investigations will be necessary in different rooms to improve uncertainty evaluation.     

Spatial extension of the acoustic time reversal region

According to the data of a full-scale shallow-water experiment (in the Barents Sea, at sea depths of about 120 m), a considerable gain in the signal-to-noise ratio is obtained for an acoustic signal received from a source at a distance of 12 km when matching with the medium is performed by the signal from the same source at a distance of 10.5 km. To interpret this experimental fact, a numerical simulation is performed to determine the size of the region of signal focusing due to the time reversal of waves in an ideal waveguide with a soft bottom. It is shown that, for narrowband signals, within a distance of ±5 km along the path from the point of emission of the reversed signal, a regular interference pattern whose maxima are comparable with the principal maximum is observed throughout the whole waveguide depth. For a spectrum width from 100 to 300 Hz, only the principle maximum with an extension of about 100 m is observed at a single depth.     

井口声发射油(气)浸入检测定位中的信号多时间延迟估计

井口声发射井筒液油气浸入定位中,通过环空内压力传感器接收反射声信号的频域分析,求其协方差矩阵特征结构,本文提出了一种信号多时间延迟快速估计方法。计算机模拟实验证实了方法的有效性.     

Contrast enhancement improves the representation of /epsilon/-like vowels in the hearing-impaired auditory nerve

This study examines the neural representation of the vowel /epsilon/ in the auditory nerve of acoustically traumatized cats and asks whether spectral modifications of the vowel can restore a normal neural representation. Four variants of /epsilon/, which differed primarily in the frequency of the second formant (F2), were used as stimuli. Normally, the rate-place code provides a robust representation of F2 for these vowels, in the sense that rate changes encode changes in F2 frequency [Conley and Keilson, J. Acoust. Soc. Am. 98, 3223 (1995)]. This representation is lost after acoustic trauma [Miller et al., J. Acoust. Soc. Am. 105, 311 (1999)]. Here it is shown that an improved representation of the F2 frequency can be gained by a form of high-frequency emphasis that is determined by both the hearing-loss profile and the spectral envelope of the vowel. Essentially, the vowel was high-pass filtered so that the F2 and F3 peaks were amplified without amplifying frequencies in the trough between F1 and F2. This modification improved the quality of the rate and temporal tonotopic representations of the vowel and restored sensitivity to the F2 frequency. Although a completely normal representation was not restored, this method shows promise as an approach to hearing-aid signal processing.     

Voice onset time as a perceptual cue in voicing contrast in Tulu language

Voice onset time (VOT) is a perceptual cue in voicing contrast of stops in the word initial position. The current study aims to acoustically and perceptually characterize VOT in one of the major South Indian languages — Tulu. Stimuli consisted of 2 pairs of meaningful words with velar [/p/-/b/] and bilabial stops and [/k/-g/] in the initial position. These words were uttered by 8 normal native speakers of Tulu and recorded using Praat software. Both spectrogram and waveform views were used to identify the VOT. For perceptual experiment, 4 adult native speakers of Tulu were asked to identify the stimulus from where voicing was truncated in steps of 5 to 7 ms till lead VOT was 0 and silence was added after the burst in 5 msec steps till the lag VOT was 50 msec. The reaction time and the accuracy in identification were measured. Results of acoustic measurement showed no significant mean difference between lead VOTs of two voiced consonants. However, there was a significant difference between means of lag VOTs of voiceless consonants. Results of Perceptual measurement showed that as lead VOT reduces, probability of indentification of /g/ responses reduces; whereas changing VOT had little effect on reaction time and identification of /b/ responses. These results probably indicate that VOT is not necessary to perceive voiceles constants in Tulu but is necessary in the perception of voiced consonants. Thus VOT is a constant specific cue in Tulu.     

Linear time domain model of the acoustic potential field

A new time domain formulation of the acoustic wave is developed to avoid approximating assumptions of the linearized scalar wave equation that limit its validity to low Mach particle velocity modeling or to a smooth potential field in a stationary medium. The proposed model offers precision of the moving frame while retaining the form of the widely used linearized scalar wave equation although with respect to modified coordinates. It is applicable to field calculations involving transient waves with unlimited particle velocity, propagating in inhomogenous fluids or in those with time varying density. The model is based on the exact flux continuity equation and the equation of motion, both using the moving reference frame. The resulting closed-form free space scalar wave equation employing total derivatives is converted back to the partial differential form by using modified independent variables. The modified variables are related to the common coordinates of space and time following integral expressions involving transient particle velocity representing wave radiated by each point of a stationary source. Consequently, transient field produced by complex surface velocity sources can be calculated following existing surface integrals of the radiation theory although using modified coordinates. The use of the proposed model is presented in a numerical simulation of a transient velocity source vibrating at selected magnitudes, leading to the determination of the propagating pressure and velocity wave at any point.     

Temporal integration of acoustic signals by the budgerigar (Melopsittacus undulatus)

Avoidance conditioning and a modified method of limits psychophysical procedure were used to study temporal integration of tone and noise signals in the budgerigar (Melopsittacus undulatus). Integration of both tone and noise signals can be described by a negative exponential function with a time constant of about 200 ms. At very short durations there were differences in the integration of tone and noise signals. These data are similar to those reported for a number of other vertebrates, including man. Thresholds for two complex natural vocalizations of the budgerigar are similar to those of pure tones of equivalent duration.     

The aspects of the numerical modeling of acoustic oscillations of the pressure at large time scales

The influence of properties of first- and second-order accuracy finite-difference schemes and of the grid roughness in the computational domain on the prediction of amplitude-frequency responses of pressure oscillations is investigated within the framework of the problem of steady-state oscillations in a semi-closed channel. It is shown that Godunov-type first-order accuracy scheme underestimates the amplitude of high-frequency oscillations relative to experimental data. Second-order accuracy Lax–Wendroff scheme leads to qualitative coincidence of a trend of amplitude-frequency response with experimental data in terms of the harmonics number even at a relatively coarse discretization of a computational domain.     

Fluctuations of quantities averaged over time in the course of measurements

The averaging effect of measuring instruments in the course of measurements of physical quantities is considered. Formulas are obtained for the calculation of the fluctuations and time correlations, taking into account the effect of the measuring equipment for classical and quantum systems.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 72–75, June, 1978.     

A theoretical estimation of the pre-breakdown-heating time in the underwater discharge acoustic source

One of the common characteristics of the electrothermal breakdown in an underwater discharge acoustic source(UDAS) is the existence of a pre-breakdown-heating phase.In our experiment,two phenomena were observed:(1) the breakdown time that takes on high randomicity and obeys a "double-peak" stochastic distribution;(2) the higher salt concentration that reduces the residual voltage and causes 100% non-breakdown.The mechanism of electrothermal breakdown is analysed.To specify the end of the pre-breakdown-heating phase,a "border boiling" assumption is proposed,in which the breakdown time is assumed to be the time needed to heat the border water around the initial arc to 773 K.Based on this ’border boiling’ assumption,the numerical simulation is performed to evaluate the effects of two heating mechanisms:the Joule heating from the ionic current,and the radiation heating from the initial arc.The simulation results verify the theoretical explanations to these two experiment phenomena:(1) the stochastic distribution of the radius of the initial arc results in the randomicity of the breakdown time;(2) the difference in efficiency between the radiation heating and the Joule heating determines that,in the case of higher salt concentration,more energy will be consumed in the pre-breakdown-heating phase.