Wideband Noise Bursts Research Articles

Пороговая длительность звуковых сигналов для оценки приближения и удаления их источника в норме и при сенсоневральной тугоухости 2–3-й степени

The study of temporal characteristics of spatial hearing was carried out in 10 patients aged 68–83 years with sensorineural hearing loss (SNHL) (hearing loss 41–62 dB) using the method of constant stimuli and moving sound image modeling in a room with short reverberation time. Patients had no acute celebrovascular accidents, traumatic brain injuries and myocardial infarctions in their medical history. The moving sound images were created by linear variation of the amplitude of wideband noise burst sequences in the frequency range of 0.2–8 kHz, which were presented from two loudspeakers. According to the individual data obtained in the patients with SNHL of the 2nd -3rd degree, the threshold signal duration required for reliable determination of approaching and receding moving sound images varied within 300–800 ms. The average duration threshold in the group of SNHL patients was 400 ms, while in subjects with normal hearing it was 150 ms. Therefore, SNHL patients need more time for correct detection of the sound image motion direction than the subjects with normal hearing. These changes in perception may be due to the combined effect of the change in supra-threshold sound coding and the failure of the high-frequency binaural mechanism as a result of the hearing thresholds decrease.

Скрининговый метод оценки пространственной и временной разрешающей способности слуха при локализации движения по азимутальной координате

A screening method for assessment of spatial and temporal resolution of the auditory system in case of azimuthal movement localization has been suggested and approbated in this paper. An approach of free-field sound source movement modeling was chosen. It is based on change of volume balance of wideband noise bursts on two loudspeakers, placed in front of the subject and separated by 60o azimuthal angle. An assessment of minimum audible movement angles and temporal thresholds for moving sound images was performed with the usage of an adaptive psychoacoustic procedure in ranges of velocities and trajectories of sound images the hearing system most sensitive to. The assessment was performed with participation of 11 healthy adult subjects for two types of signals: 1) control signals with flat spectrum and 2) signals with the reduced fraction of high-frequencies which corresponded to moderate sensorineural hearing loss. Minimum audible movement angles were 1.3o in average, and individual temporal thresholds did not exceed 0.1 s. Both these values did not depend on spectral profile of the signals. The time for assessment of one threshold was about 1.5 minutes. Preliminary approbation of the method suggested by us on the group of six patients with sensorineural hearing loss revealed a several times increase of temporal thresholds in comparison with the same thresholds for normally hearing subjects. Duration of the experiment for assessment of one threshold for patients did not differ from subjects with normal hearing. Thus, the suggested method allows quick assessment of spatial hearing condition in both healthy subjects and patients with hearing loss.

Dynamic Correlations between Intrinsic Connectivity and Extrinsic Connectivity of the Auditory Cortex in Humans.

The arrival of sound signals in the auditory cortex (AC) triggers both local and inter-regional signal propagations over time up to hundreds of milliseconds and builds up both intrinsic functional connectivity (iFC) and extrinsic functional connectivity (eFC) of the AC. However, interactions between iFC and eFC are largely unknown. Using intracranial stereo-electroencephalographic recordings in people with drug-refractory epilepsy, this study mainly investigated the temporal dynamic of the relationships between iFC and eFC of the AC. The results showed that a Gaussian wideband-noise burst markedly elicited potentials in both the AC and numerous higher-order cortical regions outside the AC (non-auditory cortices). Granger causality analyses revealed that in the earlier time window, iFC of the AC was positively correlated with both eFC from the AC to the inferior temporal gyrus and that to the inferior parietal lobule. While in later periods, the iFC of the AC was positively correlated with eFC from the precentral gyrus to the AC and that from the insula to the AC. In conclusion, dual-directional interactions occur between iFC and eFC of the AC at different time windows following the sound stimulation and may form the foundation underlying various central auditory processes, including auditory sensory memory, object formation, integrations between sensory, perceptional, attentional, motor, emotional, and executive processes.

Sound Source Localization by Hearing Preservation Patients with and without Symmetrical Low-Frequency Acoustic Hearing

The aim of this article was to study sound source localization by cochlear implant (CI) listeners with low-frequency (LF) acoustic hearing in both the operated ear and in the contralateral ear. Eight CI listeners had symmetrical LF acoustic hearing and 4 had asymmetrical LF acoustic hearing. The effects of two variables were assessed: (i) the symmetry of the LF thresholds in the two ears and (ii) the presence/absence of bilateral acoustic amplification. Stimuli consisted of low-pass, high-pass, and wideband noise bursts presented in the frontal horizontal plane. Localization accuracy was 23° of error for the symmetrical listeners and 76° of error for the asymmetrical listeners. The presence of a unilateral CI used in conjunction with bilateral LF acoustic hearing does not impair sound source localization accuracy, but amplification for acoustic hearing can be detrimental to sound source localization accuracy.

Boundary effects on the illusory continuity of and interrupted glide through a notched noise

This study investigated the illusory continuity of an interrupted frequency glide through a notched-noise burst. A 2I-2AFC procedure was used to measure detection of the (target) portion of the frequency glide that overlapped in time with the noise. The portions of the glide preceding and following the noise (flankers) could be present or absent. The center frequency of the notch coincided with either the frequency end-point of the flanker that preceded the noise, or the onset frequency of the flanker that followed the noise. A control condition with a wide-band noise burst (absent notch) was also included. Performance was poorest in the absent notch condition and was significantly poorer with present than with absent flankers. This suggests that listeners perceptually restored the missing target when flankers were present. Performance was also less accurate (indicating stronger illusory continuity) when the notch was centered on the end-point of the flanker that preceded the noise. These results suggest that the masking of the onset of the flanker following the noise provides a stronger cue to the perception of continuity than the masking of the offset of the flanker that precedes the noise.

Locating two sound sources: The role of amplitude modulation and spectral content.

We have shown that listeners can locate two sound sources producing simultaneous sounds when the sounds are independently generated wideband noise bursts. Listeners’ localization performance is better when the sound at one source is sinusoidally amplitude modulated (AM) 180 deg out‐of‐phase relative the AM of the other sound as opposed to conditions in which the envelope modulation phase is the same (in‐phase) for the sound at both sources. This improved localization performance can be measured up to AM rates of 200 Hz. Listeners can discriminate out‐of‐phase from in‐phase modulation between the two sounds up to AM rates of 500 Hz. In the current study, we use filtered noises (lowpass: 125–500 Hz, highpass: 1500–6000 Hz, and wideband: 125–6000 Hz) in an attempt to determine the role interaural time and level differences play in localizing the sources of two independently generated AM sounds. The results will be discussed in terms of the cues listeners might use in localizing multiple sound sources when the sounds occur simultaneously.

Cortical processing of speech sounds and their analogues in a spatial auditory environment

We used magnetoencephalographic (MEG) measurements to study how speech sounds presented in a realistic spatial sound environment are processed in human cortex. A spatial sound environment was created by utilizing head-related transfer functions (HRTFs), and using a vowel, a pseudo-vowel, and a wide-band noise burst as stimuli. The behaviour of the most prominent auditory response, the cortically generated N1m, was investigated above the left and right hemisphere. We found that the N1m responses elicited by the vowel and by the pseudo-vowel were much larger in amplitude than those evoked by the noise burst. Corroborating previous observations, we also found that cortical activity reflecting the processing of spatial sound was more pronounced in the right than in the left hemisphere for all of the stimulus types and that both hemispheres exhibited contralateral tuning to sound direction.

Sound localization in the human brain

Sound location processing in the human auditory cortex was studied with magnetoencephalography (MEG) by producing spatial stimuli using a modern stimulus generation methodology utilizing head-related transfer functions (HRTFs). The stimulus set comprised wideband noise bursts filtered through HRTFs in order to produce natural spatial sounds. Neuromagnetic responses for stimuli representing eight equally spaced sound source directions in the azimuthal plane were measured from 10 subjects. The most prominent response, the cortically generated N1m, was investigated above the left and right hemisphere. We found, firstly, that the HRTF-based stimuli presented from different directions elicited contralaterally prominent N1m responses. Secondly, we found that cortical activity reflecting the processing of spatial sound stimuli was more pronounced in the right than in the left hemisphere.

Noise suppression of transient-evoked otoacoustic emissions. I. A comparison with the non-linear method

A new method to record transient-evoked otoacoustic emissions (TEOAEs) is introduced. Click stimuli were presented both with and without a simultaneously presented wide-band noise burst. Subtraction of the recorded signal evoked by the noise burst plus click from the signal evoked by the click alone, cancelled the eardrum reflection components of the response and resulted in a measure of the emission. This was used to obtain the TEOAEs from 21 subjects for peak click stimulus levels of 48–66 dB SPL. The root-mean-square (RMS) level of the noise burst was set 10 dB higher than the peak click level, and resulted in suppression of the TEOAE by up to 20 dB. The TEOAE waveforms obtained by the new method were compared to those obtained with Kemp’s non-linear method, and were indistinguishable in 20 of the 21 subjects. On basis of the emission spectra, they were indistinguishable in 18 out of 21 subjects. The latencies of narrow-band filtered components from the TEOAEs obtained with the two methods were also similar. This suggests that this noise-suppression method produces similar results as Kemp’s non-linear method with the advantage that emission components with very short latencies can be obtained.

Is a common grouping mechanism involved in the phenomena of illusory continuity and stream segregation?

Two auditory phenomena--stream segregation and illusory continuity through a wide-band noise interruption--were studied to determine whether the same principles of perceptual organization applied to both. A cycle was formed of a repeating alternation of two short bursts of narrow-band noise (NBN), one centered at a high frequency (H) and the other at a low frequency (L), with shorter bursts of wide-band noise (WBN) inserted between successive NBNs (H WBN L WBN H WBN...). In some conditions, listeners could hear a single NBN moving up and down behind the WBN bursts, although there was no NBN present with the WBN. Listeners rated the strength of this illusory continuity. Center frequency separation, rate of onsets, and bandwidth of the NBNs were varied. Increases in values of all three variables decreased illusory continuity. Other listeners rated the stream segregation of the H and L bands when successive NBNs were separated either by WBN bursts (as above) or by silences. The same three acoustic variables were manipulated. Increases in all three variables decreased the perception of a single stream. The similar disruptive effects on illusory continuity and on the one-stream percept in the stream segregation task support the idea that both phenomena depend on a common preliminary process of linking together the parts of a sequence that have similar frequencies.

Detection of silent intervals between noises activating different perceptual channels: some properties of "central" auditory gap detection.

This article describes four experiments on gap detection by normal listeners, with the general goal being to examine the consequences of using noises in different perceptual channels to delimit a silent temporal gap to be detected. In experiment 1, subjects were presented with pairs of narrow-band noise sequences. The leading element in each pair had a center frequency of 2 kHz and the trailing element's center frequency was parametrically varied. Gap detection thresholds became increasingly poor, sometimes by up to an order of magnitude, as the spectral disparity was increased between the noise bursts that marked the gap. These data suggested that gap-detection performance is impoverished when the underlying perceptual timing operation requires a comparison of activity in different perceptual channels rather than a discontinuity detection within a given channel. In experiment 2, we assessed the effect of leading-element duration in within-channel and between-channel gap detection tasks. Gap detection thresholds rose when the duration of the leading element was less than about 30 ms, but only in the between-channel case. In experiment 3, the gap-detection stimulus was redesigned so that we could probe the perceptual mechanisms that might be involved in stop consonant discrimination. The leading element was a wideband noise burst, and the trailing element was a 300-ms bandpassed noise centered on 1.0 kHz. The independent variable was the duration of the leading element, and the dependent variable was the smallest detectable gap between the elements. When the leading element was short in duration (5-10 ms), gap thresholds were close to 30 ms, which is close to the voice onset time that parses some voiced from unvoiced stop consonants. In experiment 4, the generality of the leading-element duration effect in between-channel gap detection was examined. Spectrally identical noises defining the leading and trailing edges of the gap were presented to the same or to different ears. There was a leading-element duration effect only for the between channel case. The mean gap threshold was again close to 30 ms for short leading-element durations. Taken together, the data suggest that gap detection requiring a temporal correlation of activity in different perceptual channels is a fundamentally different task to the discontinuity detection used to execute gap detection performance in the traditional, within-channel paradigm.

Sound localization in the presence of multiple distracters

Listeners gave verbal apparent position estimates in response to a frozen 250 ms wideband noise burst presented from one of 36 locations in virtual free-field. A click train and a modulated harmonic complex, both presented simultaneously with the noise target, served as distracters. On each trial, the distracters were presented in one of six randomly chosen configurations in virtual space. All virtual sources were synthesized from the listeners’ own HRTFs. The impact of the distracters on the apparent position of the target varied considerably across listeners. For all listeners, when the distracters were presented on the horizontal plane at +90 degrees and −90 degrees (directly opposite the two ears), the apparent elevation and front-back position of the target were disrupted. For some listeners, this was the only effect of the distracters. In a separate condition, the stimuli were presented ten times in succession and listeners were encouraged to move their heads during stimulus presentation. Synthesis of the virtual sources was coupled to head position in order to simulate stationary virtual sources. In this condition the distracters had no effect on the apparent position of the target. [Work supported by ONR.]

The fidelity of virtual auditory displays.

A new method for on‐line virtual sound source synthesis has been developed that affords direct comparison of virtual and real sound sources. Using this method, four listeners performed a 2AFC discrimination of real free‐field sources and the virtual representations of these sources. The sources consisted of wideband noise bursts presented at a number of spatial positions. Virtual source fidelity was manipulated (on a trial by trial basis) by applying windows of various lengths (20.48, 5.12, 1.28, 0.32 ms) to the impulse responses (20.48 ms in duration) of the filters used to synthesize the virtual sources. When fidelity was highest, listeners could not discriminate virtual from real sound sources. As window length was decreased, discriminability increased. For a 1.28‐ms window, performance was above 75% correct on average. These results are consistent with physical measurements of the differences in the acoustic signal at the listener’s ear drum between virtual and real source presentation. In a related experiment, the same four listeners where asked to report the apparent positions of the virtual sound sources synthesized in the previous experiment. Degradation in localization performance was observed as filter window length was decreased. [Work supported by NASA.]

Effects of source spectrum irregularity and uncertainty on sound localization.

Localization performance has been shown to deteriorate when source spectra are variable, but the few studies investigating this have confounded trial‐to‐trial variability with spectral irregularity present in each stimulus. In this experiment these factors were varied independently. Blindfolded listeners seated in an anechoic chamber reported the apparent locations of wideband noise bursts having either smoothly sloping spectra or 1/3‐oct scrambled spectra. The spectra were either varied from trial to trial or held constant throughout an experimental session. Localization performance was compared to that obtained in a baseline condition using flat‐spectrum stimuli. Despite trial‐to‐trial uncertainty, performance with the smoothly varying spectra was equivalent to baseline. The responses to the majority of the scrambled spectrum stimuli were similar to baseline, but pronounced bias and elevated variability were observed at certain pairings of source spectrum and location that varied between listeners. The degree of uncertainty had no substantial effect on performance with these stimuli. The results suggest that source spectrum familiarity cannot effectively compensate for the interference of spectral irregularity with the processing of spectral localization cues. However, this processing appears to be surprisingly immune to such interference over much of auditory space. [Work supported by NIDCD.]

Left–right asymmetry in the buildup of echo suppression in normal-hearing adults

Echo threshold is that critical delay of a logging signal (the echo) at which the echo is "suppressed"--i.e., at which one rather than two events is perceived. It has recently been shown that echo threshold increases in most subjects when they are exposed to a train of redundant information prior to the test stimulus presentation--that is, there is buildup of echo suppression in the presence of the preceding train [Clifton et al., J. Acoust. Soc. Am. 95, 1525-1533 (1994)]. The present investigation measured echo threshold in 25 normal-hearing adult subjects, both for isolated (baseline) test stimuli and for test stimuli preceded by a redundant train of stimuli (buildup conditions). The test stimulus was a 4-microsecond wideband noise burst pair, in which the lead burst was presented from either the left or right side (from near -45 degrees or or near (+)45 degrees in different runs), and the lag burst was presented from the opposite side. Echo delay was varied adaptively, and the subject's task was to indicate on each trial which of two alternative positions (separated by 20 degrees) the lag sources was presented from. Average echo threshold in the baseline condition was 11.2 microseconds (in agreement with previous results) and did not depend on whether the lead burst was on the subject's left or right side. Average echo threshold in the buildup conditions was significantly elevated. Interestingly, there was a significantly greater buildup effect when the lead stimulus came from the subject's right side (average echo threshold: 24.4 microseconds) than when it came from the left side (average: 18.8 microseconds). This result agrees with informal observations made by Clifton and Freyman [Percept. Psychophys. 46, 139-145 (1989)] and suggests that there is more effective suppression of echo information when the lead stimulus originates from the right side (i.e., the side contralateral to the typically dominant hemisphere) that when it originates from the left side. The distribution of the magnitude of buildup effects across subjects (i.e., echo threshold in the presence of the train minus baseline echo threshold) was unimodal and symmetric, both for lag source on left (mean: 14.1 microseconds) and for lag source on right (mean: 6.7 microseconds). These results are discussed in relation to other hearing asymmetries that have been reported.

Source spectrum recovery at different spatial locations

The directional filtering of sound by the pinnae is vital to localization, but distorts the spectrum of the signal reaching the eardrum. Sounds do not appear to change character dramatically as a function of direction, so listeners might have some ability to deconvolve pinna effects from the received signal. A three-interval profile analysis task measured listeners’ ability to recover source spectra. The stimuli were wideband noise bursts in which the levels of 1/3-octave bands were adjusted to control spectral shape. They were filtered by listeners’ measured head-related transfer functions (HRTFs) and delivered via headphones. Listeners discriminated between various nonflat spectra and perturbed versions of them. HRTFs were selected randomly for each interval, and localizability was controlled by varying the correspondence of the left and right HRTFs. Thresholds were highest when HRTFs were imposed diotically, and lowest in an unfiltered diotic baseline condition. Accurate spatialization improved recovery, but applying independent near-ear HRTFs dichotically was more effective. However, deconvolution was imperfect in both conditions. The results suggest that the ability to disregard HRTF filtering and achieve some timbre constancy over direction depends on having two independent, wideband ‘‘looks’’ at the source spectrum, rather than on accurate localization.

The effects of sinusoidal amplitude modulation on gap detection in noise

The purpose of this study was to investigate the effects of envelope fluctuation on temporal gap detection. Temporal gap detection thresholds were measured in wideband noisebursts that had been amplitude modulated by a very low-frequency sinusoid. Detection was studied at six modulation depths and in four phase conditions which placed the onset of the silent gap at different amplitudes on the temporal envelope of the waveform. Gap thresholds were obtained in a 3IFC paradigm in four young, normal-hearing subjects. The smallest mean gap threshold, 3.5 ms, was obtained for unmodulated noisebursts. The largest mean gap threshold, 25.7 ms, was obtained at a modulation depth of 100%. Phase did not significantly affect gap detection until modulation depth was increased to 40%. At deeper depths of modulation, gap thresholds were smallest, but also most variable, when the gap onset was placed at a peak in the waveform envelope and largest when the gaps were centered on an envelope minimum or randomly placed. Results of this study are consistent with previous findings and the hypothesis that gap detection is dependent on the similarity of the gap itself to inherent fluctuations in the stimulus envelope, reflecting coherence in terms of phase and depth of envelope fluctuation.

Effects of amplitude modulation on gap detection in wideband noisebursts

Recent studies suggest that fluctuations in the envelopes of narrow‐band signals influence the detection of temporal gaps. In this study, the effects of amplitude modulation on gap detection using wideband noisebursts were measured by varying depth of modulation and phase angle. Gap detection thresholds were obtained for four subjects with normal hearing. The digitized noisebursts were 6 kHz in bandwidth and 150 ms in duration. The level of each noiseburst was jittered (70–75 dB SPL) and modulated with a 20‐Hz sinusoid. Gaps were placed 100 ms after stimulus onset. Gap detection thresholds were estimated at six modulation depths (0 to 100%) and at one random and three fixed phase angles. A continuous white noise (45 dB SPL) was mixed with the signals. Thresholds were obtained in an adaptive, 2IFC procedure using 100 trial runs. Twenty‐four conditions were completed in random order in 2 h. Several replications were completed by subjects. Mean gap detection thresholds increased with depth of modulation and varied with phase angle. Mean gap detection thresholds were smallest (2.5–4.0 ms) for the noisebursts which were least modulated (0–40%). Mean thresholds were largest (20 ms or more) for the noisebursts modulated 100% at a random phase. These results are consistent with recent findings using narrowband signals [B. R. Glasberg and B. C. J. Moore, Hear. Res. 64, 81–92 (1992)].

Monaural localization, revisited

There are numerous reports in the psychoacoustical literature that human listeners can localize sound sources reasonably well with one ear. Since interaural difference cues are presumably eliminated in monaural conditions, the so‐called “monaural spectral cues” introduced by pinna filtering are assumed to provide the information necessary for accurate localization in monaural conditions. In these experiments, listeners localize wideband noise bursts presented either in free‐field (with one ear occluded) or via headphones (with the signal to one phone either attenuated or disconnected). In the headphone conditions, pinna filtering effects are added digitally, such that the waveforms at a listener's eardrum are nearly the same as those produced by free‐field sources. The noise spectrum is scrambled from trial to trial to prevent learning. With the noise bursts presented at about 30 dB SL in free‐field, the results are consistent with other recent reports and suggest that some ability to localize, especially in the vertical direction, is retained in monaural conditions. However, when the identical stimuli are presented via headphones, there is no indication that sources can be localized monaurally. In other conditions, listeners localize constant spectrum stimuli, free‐field stimuli at 70 dB SL, and binaural headphone stimuli with one ear attenuated. Results from these conditions suggest that monaural localization in free‐field is most likely mediated by small head movements, a priori knowledge of the stimulus spectrum, and acoustical leakage through the ear‐occluding devices used to monauralize the listeners. [Work supported by NIH and NASA.]

SIMULTANEOUS AUDITORY DISCRIMINATION

Stimuli in many visual stimulus control studies typically are presented simultaneously; in contrast the stimuli in auditory discrimination studies are presented successively. Many everyday auditory stimuli that control responding occur simultaneously. This suggests that simultaneous auditory discriminations should be readily acquired. The purpose of the present experiment was to train rats in a simultaneous auditory discrimination. The apparatus consisted of a cage with two response levers mounted on one wall and a speaker mounted adjacent to each lever. A feeder was mounted on the opposite wall. In a go-right/go-left procedure, two stimuli were presented on each trial, a wide-band noise burst through one speaker and a 2-kHz complex signal through the other. The stimuli alternated randomly from side to side across trials, and the stimulus correlated with reinforcement for presses varied across subjects. The rats acquired the discrimination in 400 to 700 trials, and no response position preference developed during acquisition. The ease with which the simultaneous discrimination was acquired suggests that procedures, such as matching to sample, that require simultaneous presentation of stimuli can be used with auditory stimuli in animals having poor vision.