Early auditory and visual function in normal and hyperthyroid rats.
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Animals↗
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Postmasking effects of sensorineural tinnitus: a preliminary investigation.
In this study we provide some preliminary results of our attempt to measure the perception of tinnitus after the termination of a masker. The minimum level to mask tinnitus was determined for a 1-s masker in 10 subjects with sensorineural tinnitus. A continuous masker (parametrically varied in duration, frequency, and level) was then presented to the ear ipsilateral to the tinnitus. At the termination of the masker, subjects were required to press a button when their tinnitus "first returned" and a second button when it returned to "normal loudness." These response times were recorded automatically, and subjects reported what they heard after each trial. At low-level and short-duration maskers, the tinnitus typically was heard immediately after the masker termination. At higher levels and longer durations, different responses were observed. In two subjects, a silent interval was present after the masker, then the tinnitus returned at a softer loudness before returning to its premasker loudness. In one subject, the tinnitus was louder after the masker, and gradually returned to its premasker loudness. In another subject, the tinnitus returned immediately after the masker, but was softer than before. It then gradually increased to its premasker loudness. In the other two subjects, the tinnitus returned immediately to its normal loudness when the masker was terminated at all masker levels and durations. Higher level and longer duration maskers generally produced greater effects. Masker frequency, however, had little effect.
Adult↗
Cochlear microphonics and recruitment.
In this study, bilateral cochlear microphonics (CM) were evoked by tone burst simultaneously. A speaker was put in head-food axis 2 m from the mid-point of a given line connecting the bilateral external meatus. Five normal persons and 68 cases (34 cases of Meniere's disease, 27 cases of sudden hearing loss, and 7 cases of low-tone sensory hearing loss without vertigo) with unilateral sensory hearing loss and recruitment, in addition to 2 cases of bilateral Meniere's disease with recruitment were examined. CM shifted in normal and hearing loss ears and was absent in profound and totally deaf ears. When recruitment was present, CM at corresponding frequencies were enlarged and prolongated in 60 cases. Some of the enlarged and prolongated CM decayed slowly, others quickly. Meanwhile the CM of the opposite normal ear decreased obviously. The presence of enlarged and prolongated CM may indicate an increase of abnormal excitability of the hair cells caused by some pathological stimulations. This would cause excitability of the hair cells in the opposite cochlea to be inhibited by the effect of the efferent system. In such a condition, the patients complained that the stimulating sound was heard louder in the disordered ear than that in the opposite normal ear. CM was slightly enlarged during sleep.
Adult↗
Auditory memory for backward masking signals in children with language impairment.
This study was designed to investigate early auditory memory and its possible contribution to an auditory processing deficit shown by some children with language impairment. Ten children with language impairment and 10 age-matched controls participated in a series of simultaneous and backward masking tasks. The same backward masking stimulus was then used to elicit a mismatch negativity response. In the behavioral conditions, children in the language impairment group had significantly higher (poorer) signal thresholds than their nonimpaired controls in backward masking, but their thresholds in simultaneous masking were not significantly different. In the mismatch-negativity conditions, latency was prolonged and the amplitude was diminished in the children with language impairment. Taken together, these psychoacoustic and electrophysiological data suggest that in a group of children with language impairment, underlying the nonsensory language disorder, there is a neurophysiological impairment in auditory memory for complex, nonlinguistic sounds.
Attention↗
The neural processing of complex sounds.
This paper considers the temporal processing of complex sounds relevant to musical analysis. Functional imaging studies, using positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG), and the psychophysical assessment of patients with lesions allow two different approaches to this. Functional imaging allows the determination of structures normally involved in temporal analysis, while patient studies allow inference about the necessary structures for temporal analysis. Both approaches suggest a hierarchal organization in the brain corresponding to the processing of music. The features of individual notes are analyzed in the pathway up to and including the auditory cortices, while higher-order patterns formed by those features are analyzed by distributed networks in the temporal lobe and frontal lobes distinct from the auditory cortices.
Auditory Perception↗
The relative detectability for mice of gaps having different ramp durations at their onset and offset boundaries.
The effect on gap detectability of varying noise fall time (FT) and rise time (RT) of the gap boundary ramps was examined in mice using reflex modification audiometry, measuring inhibition of acoustic startle reflexes by variously shaped gaps just preceding reflex expression. In experiment 1 (n = 12) inhibition increased up to near-asymptotic values with longer FT (0, 1, 2, 3, 5, or 10 ms) and QT (quiet time, 0 to 13 ms), with a 2:1 trade-off between FT and QT. In experiment 2 (n = 24) inhibition increased for any RT above 0 ms (2, 3, 5, or 7 ms) if QT= 1 ms, but diminished with increased RT when QT = 3 or 8 ms. Enhanced detectability for subthreshold gaps by longer ramps results from their extending the apparent gap duration. The negative effect of increased RT for threshold gaps suggests the importance for gap detection of the stronger neural responses to sharp edges at the end of the gap shown previously in the mouse inferior colliculus. These effects are specific to gaps: inhibition for fixed (70-dB SPL) or varied level pulses (30 to 60 dB) was unaffected by varying the ramped edges (experiments 3 and 4, n = 9).
Animals↗
Evidence of upward spread of suppression in DPOAE measurements.
Measurements of DPOAE level in the presence of a suppressor were used to describe a pattern that is qualitatively similar to population studies in the auditory nerve and to behavioral studies of upward spread of masking. DPOAEs were measured in the presence of a suppressor (f3) fixed at either 2.1 or 4.2 kHz, and set to each of seven levels (L3) from 20 to 80 dB SPL. In the presence of a fixed f3 and L3 combination, f2 was varied from about 1 oct below to at least 1/2 oct above f3, while L2 was set to each of 6 values (20-70 dB SPL). L1 was set according to the equation L1 = 0.4L2 + 39 [Janssen et al., J. Acoust. Soc. Am. 103, 3418-3430 (1998)]. At each L2, L1 combination, DPOAE level was measured in a control condition in which no suppressor was presented. Data were converted into decrements (the amount of suppression, in dB) by subtracting the DPOAE level in the presence of each suppressor from the DPOAE level in the corresponding control condition. Plots of DPOAE decrements as a function of f2 showed maximum suppression when f2 approximately = f3. As L3 increased, the suppressive effect spread more towards higher f2 frequencies, with less spread towards lower frequencies relative to f3. DPOAE decrement versus L3 functions had steeper slopes when f2 > f3, compared to the slopes when f2 < f3. These data are consistent with other findings that have shown that response growth for a characteristic place (CP) or frequency (CF) depends on the relation between CP or CF and driver frequency, with steeper slopes when driver frequency is less than CF and shallower slopes when driver frequency is greater than CF. For a fixed amount of suppression (3 dB), L3 and L2 varied nearly linearly for conditions in which f3 approximately = f2, but grew more rapidly for conditions in which f3 < f2, reflecting the basal spread of excitation to the suppressor. The present data are similar in form to the results observed in population studies from the auditory nerve of lower animals and in behavioral masking studies in humans.
Adult↗
Speech perception, localization, and lateralization with bilateral cochlear implants.
Five bilateral cochlear implant users were tested for their localization abilities and speech understanding in noise, for both monaural and binaural listening conditions. They also participated in lateralization tasks to assess the impact of variations in interaural time delays (ITDs) and interaural level differences (ILDs) for electrical pulse trains under direct computer control. The localization task used pink noise bursts presented from an eight-loudspeaker array spanning an arc of approximately 108 degrees in front of the listeners at ear level (0-degree elevation). Subjects showed large benefits from bilateral device use compared to either side alone. Typical root-mean-square (rms) averaged errors across all eight loudspeakers in the array were about 10 degrees for bilateral device use and ranged from 20 degrees to 60 degrees using either ear alone. Speech reception thresholds (SRTs) were measured for sentences presented from directly in front of the listeners (0 degrees) in spectrally matching speech-weighted noise at either 0 degrees, +90 degrees or -90 degrees for four subjects out of five tested who could perform the task. For noise to either side, bilateral device use showed a substantial benefit over unilateral device use when noise was ipsilateral to the unilateral device. This was primarily because of monaural head-shadow effects, which resulted in robust SRT improvements (P<0.001) of about 4 to 5 dB when ipsilateral and contralateral noise positions were compared. The additional benefit of using both ears compared to the shadowed ear (i.e., binaural unmasking) was only 1 or 2 dB and less robust (P = 0.04). Results from the lateralization studies showed consistently good sensitivity to ILDs; better than the smallest level adjustment available in the implants (0.17 dB) for some subjects. Sensitivity to ITDs was moderate on the other hand, typically of the order of 100 micros. ITD sensitivity deteriorated rapidly when stimulation rates for unmodulated pulse-trains increased above a few hundred Hz but at 800 pps showed sensitivity comparable to 50-pps pulse-trains when a 50-Hz modulation was applied. In our opinion, these results clearly demonstrate important benefits are available from bilateral implantation, both for localizing sounds (in quiet) and for listening in noise when signal and noise sources are spatially separated. The data do indicate, however, that effects of interaural timing cues are weaker than those from interaural level cues and according to our psychophysical findings rely on the availability of low-rate information below a few hundred Hz.
Adult↗
A measure of internal noise based on sample discrimination.
Internal noise is often inferred from the difference between observed performance and optimum performance in detection and discrimination tasks. It can be measured directly in some cases by observing the extent to which a change in external variability impacts performance. In the studies reported here, external variability was added to an intensity discrimination task by adding a Gaussian random variable with zero mean to the overall level presented in each interval of a two-interval forced-choice task. The standard deviation of the random variable was set to half the mean difference between the levels in the two intervals, resulting in d'(ideal) = 2. As the mean difference and the corresponding standard deviation of the random variable decreased in size, performance was increasingly limited by internal noise, permitting a reliable estimate of internal noise to be obtained. This can be viewed as a sample discrimination task, with one component per sample. In the first study, performance was measured using 2-kHz tones presented at an average level of 70 dB SPL, with mean differences between distributions ranging from 0.1 to 2.2 dB in steps of 0.3 dB. The distributions were either Gaussian in level or in power. Conditions with no external variability were used to obtain a psychometric function. In the second study, performance was measured using 2-kHz tones presented at average levels of 50 and 90 dB SPL, with mean differences ranging from 0.4 to 2.2 dB in steps of 0.6 dB. In both studies, the measure of internal noise was highly reliable and in good agreement with the intensity difference limen (DL) estimated from the psychometric function. Analyses suggest that this measure could be used to estimate the mean difference between the decision distributions as well as the amount of internal noise in cases where the mean difference between the distributions is unknown.
Adolescent↗
Cochlear transducer operating point adaptation.
The operating point (OP) of outer hair cell (OHC) mechanotransduction can be defined as any shift away from the center position on the transduction function. It is a dc offset that can be described by percentage of the maximum transduction current or as an equivalent dc pressure in the ear canal. The change of OP can be determined from the changes of the second and third harmonics of the cochlear microphonic (CM) following a calibration of its initial value. We found that the initial OP was dependent on sound level and cochlear sensitivity. From CM generated by a lower sound level at 74 dB SPL to avoid saturation and suppression of basal turn cochlear amplification, the OHC OP was at constant 57% of the maximum transduction current (an ear canal pressure of -0.1 Pa). To perturb the OP, a constant force was applied to the bony shell of the cochlea at the 18 kHz best frequency location using a blunt probe. The force applied over the scala tympani induced an OP change as if the organ of Corti moved toward the scala vestibuli (SV) direction. During an application of the constant force, the second harmonic of the CM partially recovered toward the initial level, which could be described by two time constants. Removing the force induced recovery of the second harmonic to its normal level described by a single time constant. The force applied over the SV caused an opposite result. These data indicate an active mechanism for OHC transduction OP.
Acoustic Stimulation↗
Effects of level and frequency on the audibility of partials in inharmonic complex tones.
The effect of level and frequency on the audibility of partials was measured for complex tones with partials uniformly spaced on an equivalent rectangular bandwidth (ERB(N)) number scale. On each trial, subjects heard a sinusoidal "probe" followed by a complex tone. The probe was mistuned downwards or upwards (at random) by 4.5% from the frequency of one randomly selected partial in the complex. The subject indicated whether the probe was higher or lower in frequency than the nearest partial in the complex. The frequencies were roved from trial to trial, keeping frequency ratios fixed. In experiment 1, the level per partial, L, was 40 or 70 dB SPL and the mean frequency of the central partial, f(c), was 1201 Hz. Scores for the highest and lowest partials in the complexes were generally high for all spacings. Scores for the inner partials were close to chance at 0.75-ERB(N) spacing, and improved as the spacing was increased up to 2 ERB(N). For intermediate spacings, performance was better for the lower level used. In experiment 2, L was 70 dB SPL and f(c) was 3544 Hz. Performance worsened markedly for partial frequencies above 3544 Hz, consistent with a role of phase locking.
Acoustic Stimulation↗
Detecting a repeated tone burst in repeated noise.
Samples of wideband noise 0.05, 0.1, 0.2, or 0.4 s in duration were digitized and then replayed cyclically to produce repeated-noise maskers. The signal was a repeating tone burst (0.4 or 1.6 kHz). It was half the duration of the noise sample, centered in the noise temporally, and it was repeated at the same point in each repetition of the noise. In the antiphasic conditions of the experiment, either the noise sample or the tone burst was inverted in alternate repetitions of the masker; in the homophasic conditions both the tone burst and noise, or neither, were inverted in alternative repetitions. If the auditory system were capable of storing detailed waveforms of sufficient length, alternate repetitions could be added or subtracted and we might expect a release from masking in the antiphasic conditions. The results show a small but significant advantage for the antiphasic conditions when the signal frequency was 0.4 kHz, but no difference with the 1.6-kHz signal.
Adult↗
Concurrent minimum audible angle: a re-examination of the concept of auditory spatial acuity.
Minimum audible angle was measured for simultaneous acoustic events. Localization of concurrent events was found to be a direct function of the spectral differences between the events, the angle between the sources, and the location of the sources within the field defined by the subject. In the latter case, the m.a.a. was smallest with sources placed symmetrically about the listener's median plane and maximal at the extreme lateral portions. Post-hoc tests were completed which indicate that the spectral limits for concurrent localization is dependent both upon the angular separation of the sources and the position within the field as defined by the locus of the subject. The functions obtained approach the values reported by Mills [J. Acoust. Soc. Am. 30, 237-246(1958)] as the temporal overlap between the concurrent events decreased. The present results suggest that a single localization function may exist with the optimal performance observed with fully successive stimuli and poorest performance in the condition involving simultaneous events. The implications of these results are discussed.
Auditory Perception↗
Rate responses of auditory nerve fibers to tones in noise near masked threshold.
The rate responses of auditory nerve fibers were measured for best frequency (BF) tone bursts in the presence of continuous background noise. Rate functions for BF tones were constructed over a 32-dB range of levels, centered on the behavioral masked thresholds of cats. The tone level at which noticeable rate changes are evoked by the tones corresponds closely to behavioral masked threshold at all noise levels used (-10- to 30-dB spectrum level). As the noise level increases, the response rate to the background noise approaches saturation, and the incremental rate response to tones decreases. At high noise levels, the rate responses to tones of low and medium spontaneous rate fibers are larger than those of high spontaneous rate fibers. Empirical statistics of auditory nerve fiber spike counts are reported; these differ from those expected of a Poisson process in that the variance is smaller than the mean. A new measure of discharge rate is described that allows rate changes to be expressed in units of a standard deviation. This measure allows tone-evoked responses to be interpreted in terms of their detectability in a signal detection task. Rate responses of low and medium spontaneous rate fibers are more detectable than those of high spontaneous rate fibers, especially at high noise levels. There appears to be sufficient information in the rate response of a small number of auditory nerve fibers to support behaviorally observed levels of detection performance.
Acoustic Stimulation↗
Perceptual components of pitch: spatial representation using a multidimensional scaling technique.
Paired comparison experiments were carried out on the pitch of 18 computer-generated complex tones synthesized by slight modification of the frequency structure of Shepard's endless scale sounds. The results were analyzed by a multidimensional scaling technique, and simple helixes were obtained in which two components of pitch (tone height and tone chroma) were represented. Some individual differences in perception of pitch were observed according to the weight that the subject gives to each component.
Humans↗
An evaluation of eight computer models of mammalian inner hair-cell function.
Eight computer models of auditory inner hair cells have been evaluated. From an extensive literature on mammalian species, a subset of well-reported auditory-nerve properties in response to tone-burst stimuli were selected and tested for in the models. This subset included tests for: (a) rate-level functions for onset and steady-state responses; (b) two-component adaptation; (c) recovery of spontaneous activity; (d) physiological forward masking; (e) additivity; and (f) frequency-limited phase locking. As models of hair-cell functioning are increasingly used as the front end of speech-recognition devices, the computational efficiency of each model was also considered. The evaluation shows that no single model completely replicates the subset of tests. Reasons are given for our favoring the Meddis model [R. Meddis, J. Acoust. Soc. Am. 83, 1056-1063 (1988)] both in terms of its good agreement with physiological data and its computational efficiency. It is concluded that this model is well suited to provide the primary input to speech recognition devices and models of central auditory processing.
Animals↗
The role of frequency selectivity in measures of auditory and vibrotactile temporal resolution.
The purpose of this study was to compare the role of frequency selectivity in measures of auditory and vibrotactile temporal resolution. In the first experiment, temporal modulation transfer functions for a sinusoidally amplitude modulated (SAM) 250-Hz carrier revealed auditory modulation thresholds significantly lower than corresponding vibrotactile modulation thresholds at SAM frequencies greater than or equal to 100 Hz. In the second experiment, auditory and vibrotactile gap detection thresholds were measured by presenting silent gaps bounded by markers of the same or different frequency. The marker frequency F1 = 250 Hz preceded the silent gap and marker frequencies after the silent gap included F2 = 250, 255, 263, 310, and 325 Hz. Auditory gap detection thresholds were lower than corresponding vibrotactile thresholds for F2 markers less than or equal to 263 Hz, but were greater than the corresponding vibrotactile gap detection thresholds for F2 markers greater than or equal to 310 Hz. When the auditory gap detection thresholds were transformed into filter attenuation values, the results were modeled well by a constant-percentage (10%) bandwidth filter centered on F1. The vibrotactile gap detection thresholds, however, were independent of marker frequency separation. In a third experiment, auditory and vibrotactile rate difference limens (RDLs) were measured for a 250-Hz carrier at SAM rates less than or equal to 100 Hz. Auditory RDLs were lower than corresponding vibrotactile RDLs for standard rates greater than 10 Hz. Combination tones may have confounded auditory performance for standard rates of 80 and 100 Hz. The results from these experiments revealed that frequency selectivity influences auditory measures of temporal resolution, but there was no evidence of frequency selectivity affecting vibrotactile temporal resolution.
Adult↗
The effect of interaural delay of the masker on masking-level differences in young and old adults.
Diotic (SoNo) thresholds and dichotic (S pi N pi tau) thresholds were measured for young and old adults using a 500-Hz pure-tone signal and broadband burst masking noise at 37 dB SPL/Hz. In the dichotic condition both the signal and the masker were phase reversed and the masker was presented with an interaural delay of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 3, or 5 ms. Masking-level differences (MLDs) were determined by subtracting dichotic thresholds from diotic thresholds. The SoNo thresholds for the old subjects did not differ significantly from those for the young subjects; however, when MLDs were plotted as a function of delay, the pattern of results differed significantly between young and old subjects. This difference in pattern was completely accounted for in terms of a delay-line version of Durlach's equalization and cancellation (EC) model [N. I. Durlach, in Foundations of Modern Auditory Theory, edited by J. V. Tobias (Academic, New York, 1972); B. A. Schneider and P. M. Zurek, J. Acoust. Soc. Am. 86, 1756-1763 (1989)] by assuming that temporal jitter increases with internal delay in young subjects but that it does not vary with the amount of internal delay in old subjects.
Adult↗