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PubMed1988

Sound localization acuity in the cat: effect of azimuth, signal duration, and test procedure.

The sound localization acuity of cats was determined at 0 degrees, 30 degrees, 60 degrees, and 90 degrees from the median sagittal plane for four durations of noise bursts using two behavioral procedures. Similar thresholds were also obtained for humans. The cats' average thresholds for a 40 ms noise burst ranged from 4.8 degrees at 0 degrees azimuth to 9.0 degrees at 90 degrees azimuth. Comparable thresholds for humans ranged from 1.3 degrees at 0 degrees to 9.7 degrees at 90 degrees. The fact that humans and cats had similar thresholds at 90 degrees azimuth suggests that the mobile pinnae of the cat are not an advantage in localizing sound in the lateral fields. Varying the duration of the stimulus from 10 ms to 'continuous' had little effect on threshold. No difference was found between the results of the two behavioral procedures.

Adolescent↗

PubMed1991

Binaural masking level difference effects in single units of the guinea pig inferior colliculus.

We have studied the masking effects of a binaurally presented noise on the responses to binaural signals recorded from low-frequency cells in the inferior colliculus of the guinea pig. The spike rates to the masker and signal + masker were compared to quantify masking at different interaural time delays of the noise. The signal was a 50-ms tone burst at best frequency or a 50-ms segment of a synthetic vowel presented at the best interaural delay of the unit tested. At each noise masker delay, the noise level was adjusted to obtain a criterion spike difference. In most cases, the level required was lowest at the best delay for the noise. The mean difference between maximum and minimum masked thresholds across the cell population was very similar to the human psychophysical masking level difference under the same signal and masker conditions. In another series of tests, we measured the effect of the noise masker on the temporal pattern of the discharge to the signal. The signal used was a 500-ms segment of the synthetic vowel. In virtually all cases the addition of a continuous noise masker reduced the discharge rate synchronized to the fundamental frequency of the vowel. The degree of this reduction was dependent on the interaural time delay of the noise masker. For most units, maximum reduction was seen when the vowel and noise had the same interaural time delay. The similarity between the masking which we have shown physiologically and the reported in a variety of human psychophysical experiments suggests that the processing at levels up to and including the inferior colliculus contributes to the psychophysical BMLD.

Acoustic Stimulation↗

PubMed1991

Binaural amplitude discrimination and the binaural masking-level difference.

Under certain conditions, amplitude discrimination is not a monotonic increasing function of signal-to-noise ratio. The non-monotonicity arises when the tones to be discriminated are presented 180 degrees out-of-phase at the observer's ears and just above their detection 'threshold' in noise that is in-phase at the observer's ears, and with 2-6-dB differences in amplitude.

Acoustic Stimulation↗

PubMed1991

Recovery from prior stimulation. II: Effects upon intensity discrimination.

We obtained just-noticeable differences (jnds) for the intensity of pure tones following a forward masker. The masker was a 100-ms burst of narrow-band noise centered at 1000 Hz presented at 90 dB SPL; the pure-tone signal was at 1000 Hz and was 25 ms in duration. The masker-signal delay was 100 ms. Under these conditions, there is no threshold shift for the detection of the pure-tone signal following the forward masker. In contrast with the absence of a forward-masker effect upon detection thresholds, unusually large midlevel (40-60 dB SPL) jnds were observed. These large midlevel jnds were measured as a function of signal delay, revealing that they are not completely recovered to the normal (unmasked) values by 400 ms. We interpret these data as a consequence of the slower recovery of low-spontaneous rate, high-threshold neurons following prior stimulation (Relkin and Doucet, 1990). These experiments may therefore provide psychophysical evidence that the low-spontaneous rate, high-threshold neurons are a necessary physiological component in the coding of the large dynamic range for intensity. In addition, the present data provide evidence that the assumption that the effect of forward masking is limited to 100-200 ms is inappropriate, as this recovery time does not necessarily apply to suprathreshold tasks.

Acoustic Stimulation↗

PubMed1991

Temporal modulation transfer functions in the European starling (Sturnus vulgaris): I. Psychophysical modulation detection thresholds.

Temporal modulation transfer functions (TMTF) were obtained from four European starlings (Sturnus vulgaris) using a psychophysical Go/NoGo procedure combined with the method of constant stimuli. The TMTF for a continuous, broad-band noise of 55 dB SPL had a low-pass characteristic with a cut-off frequency of 123 Hz. For an 800 ms gated stimulus of the same sound-pressure level, the TMTF had the shape of a band-pass filter with the most sensitive modulation frequency at around 20 Hz. At 75 dB the band-pass shape of the TMTF was preserved, whereas at 35 dB SPL the TMTF had a low-pass characteristic. The cut-off frequency of the TMTF for continuous noise depends on which part of the spectrum carries the information on the envelope fluctuations. If only sound energy below 1 or 1.5 kHz is modulated, then the cut-off frequencies are 40 and 38 Hz, respectively. If only sound above 3 kHz carries the information on the modulation, then the cut-off frequency is 125 Hz and the shape of the TMTF is similar to that found for broadband noise. The results are discussed with respect to the coding of sinusoidal amplitude modulations by the auditory system and to different measures of time, frequency and intensity resolution in the starling.

Acoustic Stimulation↗

PubMed1992

Frequency and intensity discrimination in Mongolian gerbils, African monkeys and humans.

Frequency (delta F) and intensity (delta I) difference limens were directly compared in Mongolian gerbils (Meriones unguiculatus), Old World African Monkeys (Cercopithecus mitis, Cercocebus albigena), and humans. Methods employed a repeating background AX discrimination procedure, and positive (food) reinforcement for animals. For delta I, there were small quantitative differences between the species. At 1 kHz, 70 dB SPL, DLs averaged 2.82 dB for gerbils, 2.29 dB for monkeys, and 0.75 dB for humans. For delta F, there were larger differences between the species. At 1 kHz, 60 dB SPL, frequency DLs were highest for gerbils, averaging 108 Hz. DLs were lower for monkeys, averaging 32.6 Hz, similar to recently reported DLs for other Old World monkeys (Prosen et al., 1990). Human DLs, averaging 2.27 Hz, were markedly lower than those of either monkeys or gerbils. These results suggest that animals provide better models of human delta I than delta F.

Acoustic Stimulation↗

PubMed1993

Effects of multiple sclerosis brainstem lesions on sound lateralization and brainstem auditory evoked potentials.

Magnetic resonance (MR) imaging, brainstem auditory evoked potentials (BAEPs), and tests of interaural time and level discrimination were performed on sixteen subjects with multiple sclerosis (MS). Objective criteria were used to define MR lesions. Of the eleven subjects in whom no pontine lesions were detected and the one subject who had pontine lesions that did not encroach upon the auditory pathways, all had normal BAEPs and interaural level discrimination, although a few had abnormal interaural time discrimination. Of four subjects with lesions involving the pontine auditory pathway, all had both abnormal BAEPs and abnormal interaural time discrimination; one also had abnormal interaural level discrimination. Analysis of the data suggest the following: waves I and II are generated peripheral to the middle of the ventral acoustic stria (VAS); wave III is generated ipsilaterally in the region of the rostral VAS, caudal superior olivary complex (SOC) and trapezoid body (TB); and waves V and L are generated contralaterally, rostral to the SOC-TB. The region of the ipsilateral rostral SOC-TB is implicated as part of the pathway involved in the generation of waves V and L. Interaural time discrimination of both high and low frequency stimuli were affected by all brainstem lesions that encroached on auditory pathways. A unilateral lesion in the region of the LL affected interaural time discrimination for low-frequency stimuli less severely than bilateral lesions of the LL or a unilateral lesion of the VAS. The only interaural level discrimination abnormality occurred for a subject with a unilateral lesion involving the entire rostral VAS. It appears that detailed analysis of lesion locations coupled with electrophysiological and psychophysical data holds promise for testing hypotheses concerning the function of various human auditory brainstem structures.

Acoustic Stimulation↗

PubMed1993

Point-neuron model for binaural interaction in MSO.

A point-neuron model for the activity of individual cells in the medial superior olive (MSO) is described and shown to generate discharge patterns consistent with the activity of real neurons as reported in response to low-frequency sinusoidal stimulation. Inputs to the model cell are specified as primarylike firing patterns, and the cell membrane characteristics are specified in terms of constant-potential sources and time-varying conductances. Some conductances are determined in response to the input firings and some in response to output firing times, which are generated when the membrane potential of the model cell crosses threshold. Output firing patterns generated by the model cells are consistent with those reported from neurons in dog and cat MSO. These patterns are also compatible with those of the functionally specified coincidence model described in Colburn et al. (1990). Given these observations, the following questions are addressed: What parameter values in the point-neuron model are required to generate output patterns like those observed? How do these values compare to those expected or estimated from intracellular measurements in brainstem neurons? How might one reconcile the fact that inhibitory inputs are not necessary in the model for the generation of the observed firing patterns with the fact that MSO cells receive numerous inhibitory inputs?

Acoustic Stimulation↗

PubMed1993

The intensitive DL of tones: dependence of signal/masker ratio on tone level and on spectrum of added noise.

In Greenwood [J. Acoust. Soc. Am. 33, 484-502 (1961a)] the ratio of masked signal threshold to masker level (S/M) decreased about 4 dB at a masker level of about 50 dB SL, the 'transition' level, when noise bands were subcritical but not when supercritical. Schlauch et al. [J. Acoust. Soc. Am. 71, S73 (1982)] report a related result. A pilot study [Greenwood, Harvard Psychoacoustic Lab. Status Report 37, 8-9 (1961)] in which pure tones masked identical tones in-phase showed a larger change in S/M. Detailed tone-tone growth-of-masking curves from over a dozen subjects in 1967-69, and in 1960, are reported here. A transition in slope, of variable abruptness, often begins to occur at about 50 dB SL, dropping S/M ratio by 6 to 8 dB or more [Rabinowitz et al., J. Acoust. Soc. Am. 35, 1053 (1976)]; the curves sometimes possess two segments, sometimes are simply convex. All have overall slopes less than 1.0, known also as the 'near miss'. Consistent with other results [Zwicker, Acustica 6, 365-396 (1956); Viemeister, J. Acoust. Soc. Am. 51, 1265-1296 (1972); Moore and Raab, J. Acoust. Soc. Am. 55, 1049-1060 (1974)], addition of low-level wide-band and high-pass noise was found to counteract the change in S/M, i.e., to raise the high-level section of the growth-of-masking curve. However, the ability of narrow 'band-pass' noise to exert this effect was greatest when added at a frequency ratio (band/masking-tone) of 1.3 to 1.5, which seems more closely to link the effects of added noise to the effects of increasing a masking band from sub- to supercritical width (above). Interpretation of the decrease in DL with level begins by noting that the 'transition' level correlates approximately with the level at which a primary unit population excited by a given pure tone begins rapidly to expand basally. Underlying this, the basalward shift of a tone's displacement envelope peak accelerates at about the same level [Rhode, J. Acoust. Soc. Am. 49, 1218-1231 (1971); Sellick et al., J. Acoust. Soc. Am. 72, 131-141 (1982)].(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1993

Differential effects of age on click-rate and amplitude modulation-frequency coding in primary auditory cortex of the cat.

Recordings were made from 185 neurons in the primary auditory cortex of cats in the age range of 15 to 297 days. A comparison was made between the tuning for click repetition-rate and for amplitude modulation-frequency of a noise burst on the basis of temporal Modulation Transfer Functions (tMTF). 90 of the 185 units had a clear band-pass type tMTF for both repetition rate and modulation frequency, there was, however, no correlation between the respective Best Modulation Frequencies (BMF). Amplitude modulated noise (AMnoise) was the more effective stimulus in young kittens while click-train stimulation was more effective in adult cats. For all neurons with significant synchronization, BMFs for both click-train and AMnoise increased with age from about 4 Hz in kittens younger than 30 days to about 10 Hz in adult cats. In the approximately 50% of the neurons that were tuned both to click rate and modulation frequency, however, the BMF to AMnoise was consistently and significantly higher than that for clicks. In this group the mean BMF for kittens younger than 30 days were 7.94 Hz for AMnoise and 3.29 Hz for clicks and in the adults 10.91 Hz for AMnoise and 7.71 Hz for clicks.

Acoustic Stimulation↗

PubMed1994

Evidence of sharp frequency tuning in the human auditory cortex.

The frequency tuning of the human auditory cortex was studied by masking 100-ms tones of 1 and 2 kHz by continuous white-noise maskers with frequency notches around the tone frequencies. The subjects ignored the stimuli and concentrated on a reading task. The neuronal activity elicited by the test tones in the auditory cortex was measured with a 24-channel neuromagnetometer. The masker affected the amplitude and latency of the neuromagnetic N100m response, peaking about at 100 ms after stimulus onset, in a systematic way: the wider the notch, the shorter was the latency and the larger the amplitude. The source location of N100m in the auditory cortex did not depend on the notch width. Auditory filters at 1 and 2 kHz were modelled by a single-parameter rounded-exponential [Roex(p)] filter, based on the amplitude changes of N100m. The filters revealed sharp tuning of the auditory cortex, resembling that obtained in psychoacoustical masking studies. The results demonstrate that frequency tuning of the neurons or neuron ensembles in the human auditory cortex can be studied completely noninvasively. Moreover, since the stimuli were ignored by the subjects, the filter shape is not affected by the criterion adopted by the subject in the discrimination task.

Acoustic Stimulation↗

PubMed1994

Role of acoustic striae in hearing: mechanism for enhancement of sound detection in cats.

We report the results of behavioral studies in cats conducted first, to demonstrate the presence of a monaural mechanism for the enhancement of signal to noise; and then to examine the necessity or sufficiency of the acoustic striae for this mechanism. The results show that cats do indeed have a monaural mechanism for enhancing the detection of tones in co-located background noise for noise levels at least as high as 60 dB SPL. The ablation-behavior results show that surgical section of the dorsal (DAS) and most of the intermediate (IAS) striae has no measurable effect on this mechanism. In sharp contrast, even partial section of the trapezoid body results in a profound and permanent deficit and this deficit is not accounted for by hearing loss alone. It is concluded that the ascending and descending fibers in the dorsal and intermediate acoustic striae are neither necessary nor sufficient for enhancing the detection of salient sounds in a noisy environment while the ascending or descending fibers in the ventral acoustic stria are sufficient and probably necessary.

Acoustic Stimulation↗

PubMed1994

Detection of bandlimited noise masked by wideband noise in the chinchilla.

Six chinchillas were trained to detect a 1 s bandlimited noise signal in the presence of a continuous, wideband noise masker. As the bandwidth of the noise signal increased, there was a decrease in detection threshold. Threshold signal-to-noise ratios for the bandlimited noise signal were independent of the level of the noise masker. The slope of the bandwidth function obtained for the chinchilla is similar to the slopes reported for human subjects, approximating the predicted slope of the ideal energy detector.

Acoustic Stimulation↗

PubMed1994

Binaural processing in the dorsal nucleus of the lateral lemniscus.

We studied the binaural properties of 72 neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the mustache bat. There are six main findings: 1) Conventional EI neurons that were excited by stimulation of the contralateral ear and inhibited by ipsilateral stimulation, comprise the majority (80%) of binaural DNLL cells. 2) For most EI neurons the quantitative features of their interaural intensity disparity (IID) functions, maximum inhibition, dynamic range and 50% point IIDs, were largely unaffected by the absolute intensity at the contralateral ear. 3) Although the net effect of the inhibition evoked by ipsilateral stimulation was to suppress discharges evoked by contralateral stimulation, our results indicate that the inhibitory inputs can act in three different ways. The first was a time-intensity trade, where increasing the intensity at the ipsilateral ear evoked inhibitory effects with progressively shorter latencies. The second way was that the latency of inhibition did not appear to decrease with ipsilateral intensity, but rather increasing ipsilateral intensity appeared only to increase the strength of the inhibition. The third way was that the lowest effective ipsilateral intensity suppressed the first spikes evoked by the contralateral stimulus and higher ipsilateral intensities then suppressed the later discharges of the train. Each of these inhibitory patterns was seen in about a third of the cells. 4) Neurons that had more complex binaural properties, such as the facilitated EI neurons (EI/F) and neurons that were driven by sound to either ear (EE neurons), represented about 20% of the binaural population. There were two types of EE neurons; those in which there was a simple summation of discharges evoked with certain IIDs, and those in which the spike-counts to binaural stimulation at certain IIDs were greater than a summation of the monaural counts and thus were facilitated. 5) All binaural neurons were strongly inhibited with IIDs that favored the ipsilateral ear. Our findings indicate that the more complex binaural types, the facilitated EI neurons (EI/F) as well as the two types of EE neurons, may be constructed from conventional EI neurons by adding inputs from several sources that impart the more complex features to these neurons. We propose four circuits that could account for the different binaural response properties that we observed. The circuits are based on the known connections of the DNLL and the neurochemistry of those connections. Finally, we compared the binaural properties of neurons in the mustache bat DNLL with those of neurons in the mustache bat inferior colliculus and lateral superior olive.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed2026

Utility of hearing aid use on neurocognitive functions and auditory processing: A systematic review.

PURPOSE: Hearing loss not only affects the peripheral auditory system but also leads to changes in central auditory pathways and neurocognitive skills. The use of hearing aids has shown potential benefits in mitigating the adverse effects of hearing loss. Earlier literature showed various studies assessing the impact of hearing aid use on cognitive functions and auditory processing, a comprehensive review of the existing literature is warranted. Existing literature showed heterogeneous outcomes among studies investigated the effect of Hearing aid use in combating the adverse effects of hearing loss on neurocognitive functions and auditory processing. METHOD: Databases including PubMed, SciELO, Cochrane Library, PsycINFO, Web of Science, and Index Copernicus were searched (2005-2025) using English keywords on hearing aid effects on neurocognition and auditory processing in individuals with hearing loss. Studies on effect of hearing aid use on neurocognition and auditory processing were included, while those involving cochlear implant users or other neurological disorders unrelated to hearing loss were excluded. Titles, authors and publication years were examined, and duplicates were removed. RESULTS: Total of 61 research papers were found on specific area and were included in the present review. Findings of these 61 articles have been analysed and are reported in this article. The outcome of the present study showed usefulness of hearing aid use on neurocognitive functions and auditory processing. CONCLUSION: The present literature review emphasized the importance of early rehabilitation through hearing aid use to alleviate the adverse effects of hearing loss on neurocognitive function and auditory processing.

Humans↗

PubMed2006

Corpus callosum size is linked to dichotic deafness and hemisphericity, not sex or handedness.

Individuals differ in the number of corpus callosum (CC) nerve fibers interconnecting their cerebral hemispheres by about threefold. Early reports suggested that males had smaller CCs than females. This was often interpreted to support the concept that the male brain is more "lateralized" or "specialized," thus accounting for presumed male predominance in mathematics, as well as for aggressive behavior. Ultimately, meta-analyses of these many reports found no significant overall sex differences in inter-cerebral information carrying capacity. Here, using quantitative MRI, we found the midline CC area of 113 subjects was significantly correlated, not with handedness or sex, but with dichotic deafness, and even more so with redefined hemisphericity, the latter accounting for over 19% of CC variability. That is, both dichotic hearing and right brain-oriented individuals of either sex had significantly larger CCs than dichotically deaf or left brain-oriented persons. Thus, current traditions of brain laterality and gender may benefit from revisions that include redefined hemisphericity.

Adolescent↗

PubMed2006

Calibration of acoustic transients.

This article reviews the appropriate stimulus parameters (click duration, toneburst envelope) that should be used when eliciting auditory brainstem responses from mice. Equipment specifications required to calibrate these acoustic transients are discussed. Several methods of calibrating the level of acoustic transients are presented, including the measurement of peak equivalent sound pressure level (peSPL) and peak sound pressure level (pSPL). It is hoped that those who collect auditory brainstem response thresholds in mice will begin to use standardized methods of acoustic calibration, so that hearing thresholds across mouse strains obtained in different laboratories can more readily be compared.

Acoustic Stimulation↗

PubMed2006

Neurophysiological evidence for selective auditory attention deficits in children with specific language impairment.

Recent behavioral studies suggest that children with poor language abilities have difficulty with attentional filtering, or noise exclusion. However, as behavioral performance represents the summed activity of multiple stages of processing, the temporal locus of the filtering deficit remains unclear. Here, we used an event-related potential (ERP) paradigm to compare the earliest mechanisms of selective auditory attention in 12 children with specific language impairment (SLI) and 12 matched control children. Participants were cued to attend selectively to one of two simultaneously presented narrative stories. The stories differed in location (left/right speaker), narration voice (male/female), and content. ERPs were recorded to linguistic and nonlinguistic probe stimuli embedded in the attended and unattended story. By 100 ms, typically developing children showed an amplification of the sensorineural response to attended as compared to unattended stimuli. In contrast, children with SLI showed no evidence of sensorineural modulation with attention, despite behavioral performance indicating that they were performing the task as directed. These data are the first to show that SLI children have marked and specific deficits in the neural mechanisms of attention and, further, localize the timing of the attentional deficit to the earliest stages of sensory processing. Deficits in the effects of selective attention on early sensorineural processing may give rise to the diverse set of sensory and linguistic impairments in SLI children.

Acoustic Stimulation↗