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PubMed1985

Sensitivity of auditory-nerve fibers to changes in intensity: a dichotomy between decrements and increments.

Adaptation of auditory-nerve responses was investigated by applying increments and decrements in intensity to an ongoing tonal background. The change in firing rate produced by a change in intensity was obtained as a function of the time delay from the onset of the background to the onset of the change in intensity. The initial change in firing rate was measured using both small (1 ms) and large (10 ms) time intervals in order to evaluate properties of rapid and short-term adaptation, respectively. Consistent with previous results, the incremental and decremental responses measured with large windows were independent of time delay and the amount of prior adaptation. A similar additivity was observed for the incremental response measured with a small time window. In contrast, the decremental response measured with a small window decreased with increasing time delay and in proportion to the decrease in firing rate produced by the background. A similar decrease was observed in the response modulation produced by sinusoidal amplitude modulation. It was concluded that sensitivity to decrements in intensity decreases during adaptation, so that this response component does not reflect the additivity inherent in other aspects of adaptation.

Acoustic Stimulation↗

PubMed1986

Pure-tone pitch anomalies. II. Pitch-intensity effects and diplacusis in impaired ears.

Pitch-intensity functions and psychophysical tuning curves (PTC's) were measured in ten listeners with sensorineural impairments of presumed cochlear origin. Masking patterns, frequency jnd's, diplacusis measurements, and octave adjustments were also obtained for selected conditions in selected listeners. The results showed a tendency for increased frequency jnd's and increased pitch-matching variability in frequency regions where frequency resolution, as determined by PTC Q10 estimates, was degraded. The results also showed exaggerated pitch-level effects, both in regions where frequency resolution was degraded and, in many cases, in regions where thresholds and frequency resolution were apparently normal. The usual manifestation of exaggerated pitch-level effect was an abnormally large negative pitch shift with increasing level, particularly at low frequencies. The limited data from diplacusis measurements and octave adjustments suggest that the exaggerated negative pitch shifts are the consequence of a large increase in pitch at low stimulus levels which "recruits" at higher levels. These results are difficult to explain with simple tonotopic models, or presently formulated temporal models, of pure-tone pitch encoding.

Acoustic Stimulation↗

PubMed1986

Discrimination of interaural temporal disparities by normal-hearing listeners and listeners with high-frequency sensorineural hearing loss.

Thresholds of ongoing interaural time difference (ITD) were obtained from normal-hearing and hearing-impaired listeners who had high-frequency, sensorineural hearing loss. Several stimuli (a 500-Hz sinusoid, a narrow-band noise centered at 500 Hz, a sinusoidally amplitude-modulated 4000-Hz tone, and a narrow-band noise centered at 4000 Hz) and two criteria [equal sound-pressure level (Eq SPL) and equal sensation level (Eq SL)] for determining the level of stimuli presented to each listener were employed. The ITD thresholds and slopes of the psychometric functions were elevated for hearing-impaired listeners for the two high-frequency stimuli in comparison to: the listener's own low-frequency thresholds; and data obtained from normal-hearing listeners for stimuli presented with Eq SPL interaurally. The two groups of listeners required similar ITDs to reach threshold when stimuli were presented at Eq SLs to each ear. For low-frequency stimuli, the ITD thresholds of the hearing-impaired listener were generally slightly greater than those obtained from the normal-hearing listeners. Whether these stimuli were presented at either Eq SPL or Eq SL did not differentially affect the ITD thresholds across groups.

Acoustic Stimulation↗

PubMed1986

Interaural correlation discrimination: II. Relation to binaural unmasking.

Many theoretical models of binaural interaction assume that sensitivity to interaural correlation underlies binaural unmasking. This paper explores the extent to which sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation measured directly in correlation discrimination experiments. The vehicle for this exploration is a simplified model of the underlying processes assumed by many models of binaural unmasking for the detection of narrow-band signals in the presence of broadband noise. Consideration is given to psychometric function slopes, detection thresholds, bandwidth effects, duration effects, level effects, and interaural-parameter effects. Although many of the results obtained from our analysis are consistent with the notion that the cue in binaural detection tasks is a change in interaural correlation, some significant inconsistencies are noted.

Acoustic Stimulation↗

PubMed1986

Performance in several binaural-interaction experiments.

The relationship between interaural correlation discrimination and binaural detection was investigated using common experimental procedures and common subjects. Psychometric functions were obtained for four normal-hearing subjects at 500 and 4000 Hz using third-octave noise signals for the correlation discrimination experiment, and pure-tone signals and third-octave noise maskers for the detection experiment. Results from these two measurements, which were compared by expressing the signal-to-noise ratio as an equivalent change in interaural correlation, support the idea that interaural correlation discrimination and binaural detection are closely related. Since large intersubject differences in binaural performance were observed in these experiments, interaural-time, interaural-intensity, and monaural-intensity discrimination were measured in a second experiment. The results of the second experiment show large intersubject differences for the interaural tasks, but not for the monaural task.

Acoustic Stimulation↗

PubMed1986

Auditory spaciousness: some further psychoacoustic analyses.

Psychoacoustic investigations have confirmed the known high correlation of auditory spaciousness and preference in concert-hall types of sound fields. Further, they have provided exploratory results which gave rise to the following interpretations: Auditory spaciousness is a multidimensional perceptual attribute, predominantly caused by early lateral reflections. Low-frequency reverberation may also contribute slightly, but is sensitive with respect to individual taste. All spectral components of early lateral reflections contribute to spaciousness. Spectral restriction of the reflections leads to less favorable judgments. Early lateral reflections which do not contain spectral components above about 3 kHz mainly create image expansion in the front-back direction, thus adding to the sense of envelopment of the listener. If components above about 3 kHz are present, image broadening is prominent. By means of a model of binaural signal processing which takes interaural arrival-time differences as well as interaural level differences into account, a quasiobjective measure of auditory spaciousness can be derived.

Adult↗

PubMed1986

Frequency and amplitude perturbation analysis of electroglottograph during sustained phonation.

Electroglottography (EGG) was used to monitor vocal fold vibration patterns in normal subjects and patients with various laryngeal disorders. In order to evaluate the regularity of vocal fold vibration, frequency and amplitude perturbation of EGG waves during sustained phonation were measured with a laboratory computer. The data were compared to the degree of hoarseness evaluated by auditory perception and by sound spectrographic analysis. Frequency and amplitude perturbation measures showed some overlap between normal and pathological groups. However, there was a close relation between perturbation analysis of EGG waves and degree of hoarseness (Spearman's rank correlation coefficient rs = 0.73, p less than 0.0005). Amplitude perturbation was found to be a more sensitive measure of the irregularity of vocal fold vibration than frequency perturbation.

Adolescent↗

PubMed1986

Extension of a binaural cross-correlation model by contralateral inhibition. II. The law of the first wave front.

This paper explains the "law of the first wave front" and related binaural phenomena on the basis of the model presented in the previous paper [Lindemann, J. Acoust. Soc. Am. 80, 1608-1622 (1986)] in which a contralateral inhibition mechanism was added to the well-known model of binaural cross correlation. In order to verify the predictions of the extended model, psychoacoustic experiments were performed with pairs of narrow-band impulses which were presented through headphones. The test signals consisted of a diotic primary sound and an "echo" with an interaural arrival-time difference. Lateralization was measured as a function of the time delay between primary sound and echo. For delays below the echo threshold, summing localization and the law of the first wave front were simulated; for delays above the echo threshold, the model predicts an influence of the primary sound on the lateralization of the echo.

Auditory Perception↗

PubMed1987

Audibility and recognition of stop consonants in normal and hearing-impaired subjects.

The purpose of this study was to examine the effect of spectral-cue audibility on the recognition of stop consonants in normal-hearing and hearing-impaired adults. Subjects identified six synthetic CV speech tokens in a closed-set response task. Each syllable differed only in the initial 40-ms consonant portion of the stimulus. In order to relate performance to spectral-cue audibility, the initial 40 ms of each CV were analyzed via FFT and the resulting spectral array was passed through a sliding-filter model of the human auditory system to account for logarithmic representation of frequency and the summation of stimulus energy within critical bands. This allowed the spectral data to be displayed in comparison to a subject's sensitivity thresholds. For normal-hearing subjects, an orderly function relating the percentage of audible stimulus to recognition performance was found, with perfect discrimination performance occurring when the bulk of the stimulus spectrum was presented at suprathreshold levels. For the hearing-impaired subjects, however, it was found in many instances that suprathreshold presentation of stop-consonant spectral cues did not yield recognition equivalent to that found for the normal-hearing subjects. These results demonstrate that while the audibility of individual stop consonants is an important factor influencing recognition performance in hearing-impaired subjects, it is not always sufficient to explain the effects of sensorineural hearing loss.

Adult↗

PubMed1987

Masking effects in binaural detection and interaural time discrimination.

This study was designed to investigate the effects of masker level and frequency on binaural detection and interaural time discrimination. Detection and interaural time discrimination of a 700-Hz sinusoidal signal were measured as a function of the center frequency and level of a narrow-band masking noise. The masker was a continuous, diotic, 80-Hz-wide noise that varied in center frequency from 250 to 1370 Hz. In the detection experiment, the signal was presented either diotically (NoSo) or interaurally phase reversed (NoS pi). In the interaural time discrimination experiment, the signal level needed to discriminate a 30-microseconds interaural delay was measured. As would be expected, the presence of the masker has a greater effect on NoSo detection than NoS pi detection, and for masker frequencies at or near the signal frequency. In contrast, interaural time discrimination can be improved by the presence of a low-level masker. Also, performance improves more rapidly as the signal/masker frequency separation increases for NoSo detection than for interaural time discrimination and NoS pi detection. For all three tasks, significant upward spread of masking occurs only at the highest masker level; at low masker levels, there is a tendency toward downward spread of masking.

Adult↗

PubMed1987

Influence of place synchrony on detection of a sinusoid.

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone-burst signal, a 100-Hz-wide masker band centered at the signal frequency, and a second 100-Hz-wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100-Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.

Auditory Fatigue↗

PubMed1987

Detection of simple and complex changes of spectral shape.

In most of the previous studies (see Green, 1987) concerning the detection of a change in spectral shape, or "profile analysis," the listener's task was to detect an increment to a single component of an otherwise equal-amplitude, multicomponent background. An important theoretical issue is whether listeners' sensitivity to more complex spectral changes can be predicted from these results. In the present investigation, the sensitivity of a single group of listeners to a wide variety of simple and complex spectral changes was determined. After collecting the data, it was noted that almost all the thresholds could be predicted by a simple calculation scheme that assumed detection of a change in spectral shape occurs when the addition of the signal to the flat, multicomponent background produces a sufficient difference in level between only two regions of the spectrum. Unfortunately, this scheme, while successful for our limited set of data, fails to account for other "profile" data, namely, those obtained when the number of components is altered.

Acoustic Stimulation↗

PubMed1987

Edge effects on frequency discrimination of tones presented in low- and high-pass noise backgrounds.

Previous research has indicated that frequency discrimination performance is poorer for tones presented near the sharp spectral edge of a low-pass noise than for tones presented near the edge of a high-pass noise, or for tones in the same low-pass noise with high-pass noise added [Emmerich et al., J. Acoust. Soc. Am. 80, 1668-1672 (1986)]. The present study extends these findings in order to investigate how the steepness of the spectral edges of low- and high-pass maskers influences the discriminability of tones presented near these edges. Frequency discrimination was measured in each of three high- and low-pass noise backgrounds (which differed in the steepness of their filter skirts). The following results were obtained: (1) In the low-pass noise background, frequency discrimination performance improved as the filter skirt became more gradual; (2) in the high-pass noise background, performance first improved and then became poorer as the filter skirt became shallower; and (3) performance in low-pass noise was poorer than that in high-pass noise for the two steepest slopes employed (96 and 72 dB/oct) but not for the shallower slope (36 dB/oct). Results are discussed in the context of lateral suppression and edge pitch effects, and of a trade-off between possible edge effects and masking.

Acoustic Stimulation↗

PubMed1987

Auditory intensity discrimination in the chinchilla.

A positive reinforcement conditioning procedure was used to train chinchillas to respond to intensity differences between successively occurring tone bursts. Intensity difference limens were measured at 0.5, 1, 4, and 8 kHz at five intensities ranging from 10- to 55-dB sensation level. The intensity difference limen decreased from approximately 8 dB near threshold to approximately 3.5 dB at the highest level. The intensity difference limens for the chinchilla were considerably larger than those for humans as well as several other mammals; however, the results were similar to those obtained for the parakeet. The present results from intensity discrimination appeared to be related to previous data for the discrimination of amplitude modulated noise.

Acoustic Stimulation↗

PubMed1988

Detectability of tonal signals with changing interaural phase differences in noise.

Detectability of binaurally presented 400- and 800-Hz tonal signals was investigated in an adaptive, two-interval forced-choice experiment. A continuous 3150-Hz low-pass noise masker was presented either diotically (No), interaurally uncorrelated (NU), or interaurally phase-reversed (N pi), at an overall level of 70 dB SPL. Signal duration was either 100 or 1000 ms. The interaural phase difference (IAPD) of the signal was either fixed (0 degree-180 degrees) or time-varying (slightly different frequencies were presented to the two ears). The range of interaural phase variations was selected to yield the same varying interaural temporal differences that would be produced if real auditory targets moved through various arcs in the horizontal plane. In no case was a signal with varying IAPD any more (or less) detectable than would be expected from averaging subjects' performance in the corresponding fixed-IAPD conditions through which the variation occurred. However, in detecting these signals, subjects placed relatively more weight on the temporal central portion than on either the onset or offset. It is proposed that this weighting effect is based on two factors: (1) the signal's 20-ms rise-decay time (i.e., the onset and offset receive less binaural weight because of monaural attenuation); and (2) the very low-pass filtering effected by the binaural system, which results in some minimum time required for it to become "fully engaged." Another finding was that signal detectability became gradually worse as the antiphasic moment in a varying-IAPD signal was moved from the temporal midpoint toward the onset. No evidence was found that a signal's onset and offset were weighted differently in a binaural signal detection task.

Acoustic Stimulation↗

PubMed1988

Noise power fluctuations and the masking of sine signals.

This article is concerned with fluctuations in noise power and with the role that such fluctuations play in the masking of sine signals by noise. Several measures of noise fluctuations are discussed: the fourth moment of the waveform, the fourth moment of the envelope, and the crest factor. Relationships among these quantities are found for cases of equal-amplitude random-phase noise and Rayleigh-distributed-amplitude noise. Of particular interest is a special non-Gaussian noise called low-noise noise in which the fluctuations are small by any of our measures. The results of frozen-noise masking experiments are reported, where the noise waveform was fixed for all stimulus presentations. In separate experiments, equal-amplitude random-phase Gaussian noise, with typical fluctuations, and low-noise noise, with almost no fluctuations were used. The data show that for a noise bandwidth less than the critical bandwidth, the masked threshold is about 5 dB lower for low-noise noise than for Gaussian noise. When the noise bandwidth is larger than the critical bandwidth, the masked threshold is the same for both kinds of noise. It is concluded that noise power fluctuations increase masked threshold by about 5 dB and that filtering by the auditory system reintroduces fluctuations into broadband low-noise noise.

Acoustic Stimulation↗

PubMed1988

Failure to obtain comodulation masking release with frequency-modulated maskers.

These experiments were intended to determine whether comodulation masking release (CMR) occurs for maskers that are modulated in frequency rather than in amplitude. In experiment I, thresholds for a sinusoidal signal were measured in the presence of two continuous sinusoidal maskers: one was centered at the signal frequency (1.0 kHz), and the other was positioned at flanking frequencies ranging from 0.5 to 2.0 kHz. The two maskers were frequency modulated (FM) by the same low-pass-noise modulator (correlated condition) or by independent noise modulators (uncorrelated condition). Thresholds were the same for the correlated and uncorrelated maskers, i.e., no CMR occurred. This was also true when the flanking band was presented in the ear opposite to that containing the signal and the on-frequency masking band. In experiment II, 25-Hz-wide noise maskers were used. The on-frequency band was sinusoidally frequency modulated, while the off-frequency band either had the same FM or no FM. Thresholds were similar for the two conditions, again indicating that no CMR occurred. The results suggest that, unlike amplitude modulation, correlated FM of the masker in different frequency bands does not give rise to a release from masking.

Acoustic Stimulation↗

PubMed1988

Resonance-frequency discrimination.

Measurements of the just-noticeable change in resonance frequency delta Fr of a second-order filter are reported. The source signal was either periodic, with or without a smooth change in fundamental frequency, or it was random white noise. These differences in the nature of the source had little effect on delta Fr. Over the investigated ranges of reference resonance frequency (Fr = 300 to 2000 Hz) and filter selectivity (Q = 1 to 36), the results are well summarized by delta Fr = 0.079 Fr/square root Q. The data were used to evaluate filter-bank models employing different filter shapes and performance-prediction schemes. A good fit to the resonance-discrimination data was obtained with filters derived in a masking study by Patterson [J. Acoust. Soc. Am. 55, 802-809 (1974)] and with performance based on use of the maximum level difference over all bands. The latter finding indicates that listeners may not make optimal use of small level differences distributed over multiple bands.

Acoustic Stimulation↗