Precursor effects on behavioral estimates of frequency selectivity and gain in forward masking.
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ABSTRACT:
SUBMITTER: Jennings SG
PROVIDER: S-EPMC2736734 | biostudies-other | 2009 Apr
REPOSITORIES: biostudies-other
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Project description:Forward masking of sinusoidal frequency modulation (FM) was measured with three types of maskers: FM, amplitude modulation (AM), and a masker created by combining the magnitude spectrum of an FM tone with random component phases. For the signal FM rates used (5, 20, and 40 Hz), an FM masker raised detection thresholds in terms of frequency deviation by a factor of about 5 relative to without a masker. The AM masker produced a much smaller effect, suggesting that FM-to-AM conversion did not contribute substantially to the FM forward masking. The modulation depth of an FM masker had a nonmonotonic effect, with maximal masking observed at an intermediate value within the range of possible depths, while the random-phase FM masker produced less masking, arguing against a spectrally-based explanation for FM forward masking. Broad FM-rate selectivity for forward masking was observed for both 4-kHz and 500-Hz carriers. Thresholds measured as a function of the masker-signal delay showed slow recovery from FM forward masking, with residual masking for delays up to 500 ms. The FM forward-masking effect resembles that observed for AM [Wojtczak and Viemeister (2005). J. Acoust. Soc. Am. 188, 3198-3210] and may reflect modulation-rate selective neural adaptation to FM.
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Project description:Cochlear hearing loss is often associated with a loss of basilar-membrane (BM) compression, which in turn may contribute to degraded processing of suprathreshold stimuli. Behavioral estimates of compression may therefore be useful as long as they are valid over a wide range of levels and frequencies. Additivity of forward masking (AFM) may provide such a measure, but research to date lacks normative data from normal-hearing (NH) listeners at high sound levels, which is necessary to evaluate data from hearing-impaired (HI) listeners. The present study measured AFM in six NH listeners for signal frequencies of 500, 1500, and 4000 Hz in the presence of background noise, designed to elevate signal thresholds to levels similar to those experienced by HI listeners. Results consistent with compressive BM responses were found for all six listeners at 500 Hz, five listeners at 1500 Hz, but only two listeners at 4000 Hz. Further measurements in the absence of background noise also indicated a lack of consistent compression at 4000 Hz at higher signal levels, in contrast to earlier results collected at lower levels. A better understanding of this issue will be required before AFM can be used as a general behavioral estimate of BM compression.
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Project description:Forward masking by harmonic tone complexes was measured for on- and off-frequency maskers as a function of masker phase curvature for two masker durations (30 and 200 ms). For the lowest signal frequency (1 kHz), the results matched predictions based on the expected interactions between the phase curvature and amplitude compression of peripheral auditory filtering. For the higher signal frequencies (2 and 6 kHz), the data increasingly departed from predictions in two respects. First, the effects of the masker phase curvature became stronger with increasing masker duration, inconsistent with the expected effects of the fast-acting compression and time-invariant phase response of basilar membrane filtering. Second, significant effects of masker phase curvature were observed for the off-frequency masker using a 6-kHz signal, inconsistent with predictions based on linear processing of stimuli well below the signal frequency. New predictions were generated assuming an additional effect with a longer time constant, consistent with the influence of medial olivocochlear efferent activation on otoacoustic emissions in humans. Reasonable agreement between the predicted and the measured effects suggests that efferent activation is a potential candidate mechanism to explain certain spectro-temporal masking effects in human hearing.
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Project description:HypothesisThe hypothesis tested was that forward masking of the speech-evoked auditory brainstem response (sABR) increases peak latency as an inverse function of masker-signal interval (Δt), and that the overall persistence of forward masking is age dependent.BackgroundOlder listeners exhibit deficits in forward masking. If forward-masked sABRs provide an objective measure of the susceptibility of speech sounds to prior stimulation, then this provides a novel approach to examining the age dependence of temporal processing.MethodsA /da/ stimulus forward masked by speech-shaped noise (Δt = 4-64 ms) was used to measure sABRs in 10 younger and nine older participants. Forward masking of subsegments of the /da/ stimulus (Δt = 16 ms) and click trains (Δt = 0-64 ms) was also measured.ResultsForward-masked sABRs from young participants showed an increase in latency with decreasing Δt for the initial peak. Latency shifts for later peaks were smaller and more uniform. None of the peak latencies returned to baseline by Δt = 64 ms. Forward-masked /da/ subsegments showed peak latency shifts that did not depend simply on peak position, while forward-masked click trains showed latency shifts that were dependent on click position. The sABRs from older adults were less robust but confirmed the viability of the approach.ConclusionForward masking of the sABR provides an objective measure of the susceptibility of the auditory system to prior stimulation. Failure of recovery functions to return to baseline suggests an interaction between forward masking by the prior masker and temporal effects within the stimulus itself.
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Project description:The current study measured the additional masking obtained for combinations of forward and simultaneous maskers as a function of forward masker bandwidth, signal delay, and simultaneous masker level. The effects of the two individual maskers were equated in all conditions. Additional masking increased with increasing masker level, increasing signal delay, and decreasing masker bandwidth. The portion of the simultaneous masker that made the greater contribution to additional masking was the part that overlapped with the signal, not with the forward masker. The changes in additional masking observed as a function of forward masker bandwidth and the interaction between the effects of forward and simultaneous maskers call into question the use of additional masking as a measure of basilar membrane compression and present problems for the use of simultaneous noise to simulate hearing loss.
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Project description:BACKGROUND:With India preparing for the next decennial Census in 2021, we compared the disability estimates and data collection methodology between the Census 2011 and the most recent population-level survey for India and its states, to highlight the issues to be addressed to improve robustness of the disability estimates in the upcoming Census. METHODS:Data from the Census 2011 and from two complementary nationally representative household surveys that covered all Indian states with the same methodology and survey instruments-the District-Level Household Survey-4 (DLHS-4, 2012-2013) and the Annual Health Surveys (AHS three rounds, 2010-11, 2011-12 and 2012-13) were used. Data from DLHS-4 and AHS 2012-13 round were pooled to generate estimates for the year 2012-13. Data collection methodology between the sources was compared, including the review of definitions of each type of disability. The overall, mental, visual, hearing, speech, and movement disability rate (DR) per 100,000 population were compared between the sources for India and for each state, and the percent difference in the respective rates was calculated. We explored the reliability of these estimates comparing yearly data from the AHS for three successive rounds. RESULTS:Survey data were collected through proxy reporting, however, it is not entirely clear whether the data were proxy- or self-reported or a mix of both in the Census. The overall DR was 25.1% higher in the Census (2,242; 95% CI 2,241-2,243) than the survey (1,791; 95% CI 1,786-1,797) per 100,000 population, with the state-level difference ranging from -64% in Tamil Nadu to 107% in Sikkim state. Despite both sources using nearly similar definitions for overall disability and disability by type, the difference in DR was 125.5%, 54.2%, -25.7%, -19.7%, and 21.9% for hearing, speech, mental, movement, and visual DR, respectively. At the state-level, the difference in disability-specific estimates ranged from -84% to 450%. The extent of variations in the disability-specific estimates in AHS successive rounds ranged from -25% to 929% at the state-level. CONCLUSIONS:There is momentum globally towards building disability measurement that is consistent with the data required for monitoring of the Sustainable Development Goals to ensure robust estimation of disability. The current estimates from the Census and surveys seem much lower than would be expected at the population level. We make recommendations that India needs to take serious note of in order to improve the validity and reliability of India's disability estimates.
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Project description:Hearing-impaired (HI) listeners often show poorer performance on psychoacoustic tasks than do normal-hearing (NH) listeners. Although some such deficits may reflect changes in suprathreshold sound processing, others may be due to stimulus audibility and the elevated absolute thresholds associated with hearing loss. Masking noise can be used to raise the thresholds of NH to equal the thresholds in quiet of HI listeners. However, such noise may have other effects, including changing peripheral response characteristics, such as the compressive input-output function of the basilar membrane in the normal cochlea. This study estimated compression behaviorally across a range of background noise levels in NH listeners at a 4 kHz signal frequency, using a growth of forward masking paradigm. For signals 5 dB or more above threshold in noise, no significant effect of broadband noise level was found on estimates of compression. This finding suggests that broadband noise does not significantly alter the compressive response of the basilar membrane to sounds that are presented well above their threshold in the noise. Similarities between the performance of HI listeners and NH listeners in threshold-equalizing noise are therefore unlikely to be due to a linearization of basilar-membrane responses to suprathreshold stimuli in the NH listeners.
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Project description:Frequency selectivity was evaluated under two conditions designed to assess the influence of a "precursor" stimulus on auditory filter bandwidths. The standard condition consisted of a short masker, immediately followed by a short signal. The precursor condition was identical except a 100-ms sinusoid at the signal frequency (i.e., the precursor) was presented before the masker. The standard and precursor conditions were compared for measurements of psychophysical tuning curves (PTCs), and notched noise tuning characteristics. Estimates of frequency selectivity were significantly broader in the precursor condition. In the second experiment, PTCs in the standard and precursor conditions were simulated to evaluate the influence of the precursor on PTC bandwidth. The model was designed to account for the influence of additivity of masking between the masker and precursor. Model simulations were able to qualitatively account for the perceptual data when outer hair cell gain of the model was reduced in the precursor condition. These findings suggest that the precursor may have reduced cochlear gain, in addition to producing additivity of masking. This reduction in gain may be mediated by the medial olivocochlear reflex.
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Project description:PurposeWe aimed to study the effect of stimulus contrast on the orientation selectivity of interocular interaction in amblyopia using a dichoptic masking paradigm.MethodsEight adults with anisometropic or mixed amblyopia and 10 control adults participated in our study. The contrast threshold in discriminating a target Gabor in the tested eye was measured with mean luminance in the untested eye, as well as with a bandpass oriented filtered noise in the other eye at low spatial frequency (0.25 c/d). Threshold elevation, which represents interocular suppression, was assessed using a the dichoptic masking paradigm (i.e. the contrast threshold difference between the target only and masked conditions), for each eye. Orientation selectivity of the interocular suppression as reflected by dichoptic masking was quantified by the difference between the parallel and orthogonal masking configurations. Two levels of mask's contrast (3 times or 10 times that of an individual's contrast threshold) were tested in this study.ResultsThe strength of dichoptic masking suppression was stronger at high, rather than low mask contrast in both amblyopic and control subjects. Normal controls showed orientation-dependent dichoptic masking suppression both under high and low contrast levels. However, amblyopes showed orientation-tuned dichoptic masking suppression only under the high contrast level, but untuned under the low contrast level.ConclusionsWe demonstrate that interocular suppression assessed by dichoptic masking is contrast-dependent in amblyopia, being orientation-tuned only at high suprathreshold contrast levels of the mask.
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