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PubMed1990

Psychophysical measures from electrical stimulation of the human cochlear nucleus.

Auditory performance on basic psychophysical tasks was measured in ten deaf patients with electrodes positioned near their cochlear nucleus. The device is called the auditory brainstem implant (ABI). Electrodes were placed during surgery to remove an acoustic neuroma, which results in the removal of the VIII nerve and, thus deafness. In patients who received auditory sensation from electrical stimulation we measured auditory performance on standard psychophysical tasks: thresholds, loudness growth, intensity discrimination, temporal integration, temporal modulation detection, gap detection, and forward masking. Plots of threshold as a function of frequency or biphasic pulse duration were markedly different from those of patients with cochlear implants. The difference in threshold functions is probably partly due to the biophysical difference in the neural elements stimulated. Another possibility is that part of the difference is due to the highly abnormal spatial pattern of activation in the cochlear nucleus from electrical stimulation, which prevents normal spatial integration of activity. The usable range of electrical amplitudes above threshold is comparable with that of cochlear implants, typically 10-15 dB. Little temporal integration occurs over a range of stimulus durations from 2-1000 ms. When compared at equivalent loudness levels, gap detection thresholds are similar to, or a bit longer than, gap thresholds in normal-hearing listeners and cochlear implant patients. Forward masking recovery functions are similar to those of normal listeners and cochlear implant patients. Patients' ability to detect amplitude modulation as a function of modulation frequency is similar to that of cochlear implant patients and normal listeners. Thus, direct electrical stimulation of the brainstem produces temporal resolution that does not significantly differ from that of normal listeners when compared in equivalent amplitude units. This implies that the limiting factors for these tasks are more centrally located, and not directly related to threshold mechanisms. Thus, a properly designed speech processor could preserve the important temporal features of speech for these patients.

Adolescent↗
PubMed1991

On the effect of interaural phase differences on loudness.

The loudness of four monaurally presented Gaussian shaped, 60-ms tone bursts was matched to that of four similar pulses presented binaurally. The stimuli to be matched were all presented in continuous binaural noise of three levels and, in different experiments, either the monaural or the binaural stimuli were adjusted by the observer. With 250- and 710-Hz tone bursts, there are large differences in loudness that, at low signal-to-noise ratios, depend on the interaural phase conditions in a manner consistent with the changes in masked threshold produced by the phase manipulation; there is little, if any, effect of interaural phase on loudness for 2-kHz signals. The effect of interaural phase on loudness decreases with increasing level but, at 250 Hz, remains measurable some 30-40 dB above masked threshold. The matching function for signals out-of-phase grows in proportion to the level to be matched over the entire range from masked threshold to the highest level used. In contrast, for the in-phase condition, the observers show a step at a level that depends both on frequency and on the observer from proportional growth near thresholds to parallel proportional growth some 6 to 12 dB higher.

Acoustic Stimulation↗
PubMed1992

Loudness balance between electric and acoustic stimulation.

Binaural loudness balance between electric and acoustic stimulation is obtained in auditory brainstem implant listeners who had substantial acoustic hearing in one ear. The data are well described by a linear relationship between acoustic decibels and electric microamps. Based upon this linear relationship, we propose an exponential model of loudness growth in electric stimulation. The exponential model predicts that the loudness growth function can be determined solely by the threshold and the uncomfortable loudness level in electric stimulation. This prediction is consistent with previous psychophysical data on loudness functions. Implications of this finding for speech processor designs are discussed.

Acoustic Stimulation↗
PubMedDate not supplied

P300 from normals and adult children of alcoholics.

The P300 event-related brain potential (ERP) was obtained from 24 pairs of undergraduate male subjects. One member of each pair reported having a father who was alcoholic (FH+), the other reported no alcoholic family member (FH-). Pairs were matched on height, weight, academic performance, and personal drinking history. Three auditory task situations were employed which manipulated stimulus discrimination difficulty. All tasks employed 20% target and 80% standard tones randomly presented with the subjects required to move their index finger whenever a target tone was detected. No differences in P300 amplitude or latency were obtained between the groups. FH+ subjects tended to demonstrate decreased amplitudes with increased amounts of reported alcohol consumption but only for the most difficult task. The results of the present study suggest that the relationship between the P300 and the heritability for alcoholism is not yet clear and may be modulated by differences in task requirements, subject populations, and personal drinking history.

Adolescent↗
PubMed2005

No evidence for qualitative differences in the processing of short and long temporal intervals.

Several lines of research suggest that two distinct timing mechanisms are involved in temporal information processing: a sensory mechanism for processing of durations in the range of milliseconds and a cognitively controlled mechanism for processing of longer durations. The present study employed a dual-task approach and a sensory interference paradigm to further elucidate the distinct timing hypothesis. Experiment 1 used mental arithmetic as a nontemporal secondary task, Experiment 2 a memory search task, and Experiment 3 a visuospatial memory task. In Experiment 4, a loudness manipulation was applied. Mental arithmetic and loudness manipulation affected temporal discrimination of both brief and long intervals, whereas the two remaining tasks did not influence timing performance. Observed differences in interference patterns may be explained by some tasks being more difficult than others. The overall pattern of results argues against two qualitatively distinct timing mechanisms, but is consistent with attention-based cognitive models of human timing.

Adult↗
PubMed2005

Effects of attention on the neural processing of harmonic syntax in Western music.

The effects of selective attention on the neural response to the violation of musical syntax were investigated in the present study. Musical chord progressions were played to nonmusicians while Event-Related Potentials (ERPs) were recorded. The five-chord progressions included 61% harmonically expected cadences (I-I(6)-IV-V-I), 26% harmonically unexpected cadences (I-I(6)-IV-V-N(6)), and 13% with one of the five chords having an intensity fadeout across its duration. During the attended condition, subjects responded by pressing a button upon detecting a fadeout in volume; during the unattended condition, subjects were given reading comprehension materials and instructed to ignore all auditory stimuli. In response to the harmonic deviant, an Early Anterior Negativity (EAN) was observed at 150-300 ms in both attention conditions, but it was much larger in amplitude in the attended condition. A second scalp-negative deflection was also identified at 380-600 ms following the harmonic deviants; this Late Negativity onset earlier during the attended condition. These results suggest strong effects of attention on the neural processing of harmonic syntax.

Acoustic Stimulation↗
PubMed2005

Selective serotonin reuptake inhibitors treatment effects on auditory measures in depressed female subjects.

The purpose of this study was to evaluate the auditory effects of selective serotonin reuptake inhibitors (SSRI), known to enhance serotonin (5-HT) transmission in the brain. The experimental group consisted of 14 clinically depressed female subjects, and the control group consisted of 11 non-depressed females. A battery of tests was administered to the experimental group while on and off of SSRI medication. The control group was also administered the test battery twice. Results indicated no significant differences in the control group between sessions. The experimental group showed significantly smaller transient evoked emissions, higher SCAN-A (auditory processing test) composite scores, and smaller amplitude growth functions for Auditory brainstem response peak V and Auditory late response peak N(1)P(2) while on SSRI medication. The increased 5-HT levels in the presence of SSRI (due to reduced reuptake of 5-HT) may be contributing to the significant changes seen in auditory measures with the experimental group.

Acoustic Impedance Tests↗
PubMed2004

A population study of the precedence effect.

Data are reported from a population of untrained individuals under lag- and single-click conditions in a discrimination suppression precedence-effect task. The cue to be discriminated was an interaural level-difference (ILD). Each of 91 observers completed 10 runs in a two-interval forced-choice design under a lag-click condition and three runs under a single-click condition. Stimuli were 125-micros rectangular pulses and the interclick interval was 2 ms. Observers were randomly assigned to three groups of approximately 30. Each group was then tested at one stimulus intensity (43, 58, or 73 dB). Mean threshold within each group was greater than 15 dB for the lag-click condition and 6 dB for the single-click condition, although there was substantial interobserver variability. In contrast to [J. Acoust. Soc. Am. 114 (2003) 420] who reported a strong effect of intensity on lag-click ITD discrimination, no effect of intensity was observed on lag-click ILD thresholds. Analysis of over 50,000 near-threshold trials from 302 observers pooled across studies showed a spatial asymmetry in response patterns and a small, but statistically significant effect of gender. A model is proposed which shows that decay of sensory memory and increases in auditory filter bandwidths with intensity may predict the different findings for ILD versus ITD lag-click thresholds.

Acoustic Stimulation↗
PubMed2004

Effects of intensity and location on sound location discrimination in macaque monkeys.

Sound localization performance is degraded at low stimulus intensities in humans, and while the sound localization ability of humans and macaque monkeys appears similar, the effects of intensity have yet to be described in the macaque. We therefore defined the ability of four macaque monkeys to localize broadband noise stimuli at four different absolute intensities and six different starting locations in azimuth. Results indicate that performance was poorest at the lowest intensity tested (25 dB SPL), intermediate at 35 dB SPL, and equivalent at 55 and 75 dB SPL. Localization performance was best at 0 degree (directly in front of the animal) and was systematically degraded at more peripheral locations (+/-30 degrees and 90 degrees) and worst at a location directly behind the animal. Reaction times showed the same trends, with reaction times increasing with decreasing stimulus intensity, even under conditions where the monkey discriminated the location change with the same performance. These results indicate that sound level as well as position profoundly influences sound localization ability.

Acoustic Stimulation↗
PubMed2005

Loudness growth in cochlear implants: effect of stimulation rate and electrode configuration.

In cochlear implant speech processor design, acoustic amplitudes are mapped to electric currents with the intention of preserving loudness relationships across electrodes. Many parameters may affect the growth of loudness with electrical stimulation. The present study measured the effects of stimulation rate and electrode configuration on loudness growth in six Nucleus-22 cochlear implant users. Loudness balance functions were measured for stimuli that differed in terms of stimulation rate, electrode configuration and electrode location; a 2-alternative, forced-choice adaptive procedure (double-staircase) was used. First, subjects adaptively adjusted the amplitude of a 100-pulse-per-second (pps) pulse train to match the loudness of a 1000-pps standard pulse train. For a range of reference stimulation levels, the loudness of the 100-pps stimulus was matched to that of the 1000-pps standard stimulus; loudness balancing was performed for three electrode pairs [(20,22), (1,3), (1,22)]. The results showed that the loudness balance functions between the 100- and 1000-pps stimulation rates were highly subject-dependent. Some subjects' loudness balance functions were logarithmic, while others' were nearly linear. Loudness balance functions were also measured across electrode locations [(20,22) vs. (1,3)] for two stimulation rates (100, 1000 pps). Results showed that the loudness balance functions between the apical and basal electrode pairs highly depended on the stimulation rate. For all subjects, at the 1000-pps rate, the loudness balance functions between the two electrode locations were nearly linear; however, at the 100-pps rate, the loudness balance function was highly nonlinear in two out of six subjects. These results suggest that, for some cochlear implant patients, low-frequency stimulation may be processed differently at different electrode locations; for these patients, acoustic-to-electric amplitude mapping may need to be sensitive to this place-dependent processing when relatively low stimulation rates are used.

Adult↗
PubMed2005

Current-level discrimination using bipolar and monopolar electrode configurations in cochlear implants.

This study examined current-level discrimination ability in listeners with cochlear implants using bipolar and monopolar electrode configurations. Current-level discrimination ability was measured as a function of electrode configuration (monopolar and bipolar), stimulation site (8 and 16) and level (5%, 15%, 25%, 50% and 80% of the dynamic range). Weber fractions usually decreased with increasing level. Differences in Weber fractions between monopolar and bipolar configurations were observed for listeners with short durations of deafness (<5 years). For these listeners, in the bipolar condition at the more-apical site 16, Weber fractions remained constant with increasing level, and the Weber fractions at low levels were smaller than in other conditions. We suggest that nerve density was better and the nerve-to-site-of-action-potential distance was smaller in these cases such that more fibers could be recruited with a unit increase in current level, leading to better current-level sensitivity.

Adult↗
PubMed2005

The auditory acclimatization effect in sensorineural hearing-impaired listeners: evidence for functional plasticity.

The present study provides new data on perceptual and physiological modifications associated with hearing aid (HA) fitting. Eight sensorineural hearing-impaired (SNHI) listeners participated. They had symmetrical hearing loss and were being fitted with binaural HAs for the first time. Perceptual performances were measured four times during auditory rehabilitation, using an intensity discrimination task and a loudness-scaling task. Pure tones of two different frequencies were used, one well amplified by HAs and the other weakly amplified. Two intensity levels were also tested, one rated 'soft' by SNHI listeners and the other 'loud'. Auditory brainstem responses (ABRs) to click stimulation were recorded. All measures were performed without HA. Results were consistent with the auditory acclimatization effect: most modifications induced by HA fitting were found at loud intensity levels and at high frequency, i.e., for acoustic information that was newly available to the listener. While both ears had similar hearing loss and aided gains, some differences between ears appeared in both perceptual tasks and in ABRs. In the right ear, a shortening of wave V latency paralleled perceptual modifications. The present results suggest that HA-fitting induces functional plasticity at the peripheral level of the auditory system.

Adaptation, Physiological↗
PubMed2005

Cochlear compression in listeners with moderate sensorineural hearing loss.

Psychophysical estimates of basilar membrane (BM) responses suggest that normal-hearing (NH) listeners exhibit constant compression for tones at the characteristic frequency (CF) across the CF range from 250 to 8000 Hz. The frequency region over which compression occurs is broadest for low CFs. This study investigates the extent that these results differ for three hearing-impaired (HI) listeners with sensorineural hearing loss. Temporal masking curves (TMCs) were measured over a wide range of probe (500-8000 Hz) and masker frequencies (0.5-1.2 times the probe frequency). From these, estimated BM response functions were derived and compared with corresponding functions for NH listeners. Compressive responses for tones both at and below CF occur for the three HI ears across the CF range tested. The maximum amount of compression was uncorrelated with absolute threshold. It was close to normal for two of the three HI ears, but was either slightly (at CFs < or =1000 Hz) or considerably (at CFs > or =4000 Hz) reduced for the third ear. Results are interpreted in terms of the relative damage to inner and outer hair cells affecting each of the HI ears. Alternative interpretations for the results are also discussed, some of which cast doubts on the assumptions of the TMC-based method and other behavioral methods for estimating human BM compression.

Acoustic Stimulation↗
PubMed2005

Effect of inter-phase gap on the sensitivity of cochlear implant users to electrical stimulation.

Human behavioral thresholds for trains of biphasic pulses applied to a single channel of Nucleus CI24 and LAURA cochlear implants were measured as a function of inter-phase gap (IPG). Experiment 1 used bipolar stimulation, a 100-pps pulse rate, and a 400-ms stimulus duration. In one condition, the two phases of each pulse had opposite polarity. Thresholds continued to drop by 9-10 dB as IPG was increased from near zero to the longest value tested (2900 micros for CI24, 4900 micros for LAURA). This time course is much longer than reported for single-cell recordings from animals. In a second condition, the two phases of each pulse had the same polarity, which alternated from pulse to pulse. Thresholds were independent of IPG, and similar to those in condition 1 at IPG=4900 micros. Experiment 2 used monopolar stimulation. One condition was similar to condition 1 of experiment 1, and thresholds also dropped up to the longest IPG studied (2900 micros). This also happened when the pulse rate was reduced to 20 pps, and when only a single pulse was presented on each trial. Keeping IPG constant at 8 micros and adding an extra biphasic pulse x ms into each period produced thresholds that were roughly independent of x, indicating that the effect of IPG in the other conditions was not due to a release from refractoriness at sites central to the auditory nerve. Experiment 3 measured thresholds at three IPGs, which were less than, equal to, and more than one half of the interval between successive pulses. Thresholds were lowest at the intermediate IPG. The results of all experiments could be fit by a linear model consisting of a lowpass filter based on the function relating threshold to the frequency of sinusoidal electrical stimulation. The data and model have implications for reducing the power consumption of cochlear implants.

Action Potentials↗
PubMed2005

Simultaneous suppression of tone burst-evoked otoacoustic emissions--effect of level and presentation paradigm.

There is conflict in the literature over whether individual frequency components of a transient-evoked otoacoustic emission (TEOAE) are generated within relatively independent "channels" along the basilar membrane (BM), or whether each component may be generated by widespread areas of the BM. Two previous studies on TEOAE suppression are consistent with generation within largely independent channels, but with a degree of interaction between nearby channels. However, both these studies reported significant suppression only at high stimulus levels, at which the "nonlinear" presentation paradigm was used. The present study clarifies the separate influences of stimulus level and presentation paradigm on this type of suppression. TEOAEs were recorded using stimulus tone bursts at 1, 2 and 3 kHz and a complex stimulus consisting of a digital addition of the three tone bursts, over a range of stimulus levels and both "linear" and "nonlinear" presentation paradigms. Responses to the individual tone bursts were combined offline and compared with responses to the complex stimuli. Results clearly demonstrate that TEOAE suppression under these conditions is dependent upon stimulus level, and not upon presentation paradigm. It is further argued that the data support the "local" rather than "widespread" model of TEOAE generation, subject to nonlinear interactions between nearby generation channels.

Acoustic Stimulation↗
PubMed2006

Psychophysical measures in patients fitted with Contour and straight Nucleus electrode arrays.

The objective of this study was to compare the psychophysical performance of patients using the Nucleus Contour electrode array with that of patients using the straight banded-electrode array. In particular, we wished to consider how psychophysical parameters would differ for an electrode array positioned closer to the modiolus, and how this might influence both patient benefits and the design of speech processing strategies. Nine subjects participated in the study: four used the Nucleus straight array and five used the Nucleus Contour electrode array. Radiographic analyses found that the Contour array lay closer to the modiolus, was more deeply inserted and spanned a larger fractional length of the basilar membrane than the straight banded-electrode array. The results were analysed in terms of array type and of the position of the individual electrode band, both distance from the modiolus and longitudinal placement. Mean threshold was lower for the Contour array but maximum comfortable level was similar. Whereas threshold varied significantly with distance of electrode band from the modiolus, maximum comfortable level did not. Pitch varied fairly regularly with longitudinal position of the stimulated electrode, with the exception of one Contour subject. The forward masking profiles, using moderately loud maskers, were narrower for the Contour array, indicative of more localized neural excitation.

Acoustic Stimulation↗
PubMed2006

Contextual modulation of cochlear hearing desensitization depends on the type of loud sound trauma.

In ears in which cochlear efferent pathways were cut and with testing done under anaesthetic conditions that preclude middle ear muscle activity (so as to examine the "intrinsic" effects of loud sound on the cochlea without any confounding effect of efferent pathways to the auditory periphery), atraumatic background white noise (WN) increases cochlear hearing loss (temporary threshold shifts, TTSs) induced by a traumatic pure tone but reduces TTSs caused by traumatic 5-kHz wide narrow band (NB) sound. The short-duration moderately intense traumata used in these studies most likely cause TTSs by affecting cochlear mechanics and these WN modulatory effects, exerted directly on the cochlea's intrinsic susceptibility to TTSs, are not predicted by any current description of cochlear mechanics. Here it is demonstrated that background WN reduces trauma-induced TTSs with even a relatively small increase in trauma bandwidth beyond that of a pure tone, discounting the alternative that contextual modulatory effects transition systematically along a continuum as trauma bandwidth increases from a pure tone to a broader bandwidth (albeit 2 kHz-wide NB) trauma. These results have implications for cochlear mechanics as the TTSs due to the traumatic sound of this study are most likely due to changes in cochlear mechanics but are not easily explained by what is currently known of cochlear mechanics.

Acoustic Stimulation↗