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Results for “Auditory Perception”

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At least 1,279 records · Page 71Linked to original sources

PubMed2004

Peripheral compression as a function of stimulus level and frequency region in normal-hearing listeners.

Fixed-probe-level temporal masking curves (TMCs) were obtained from normal-hearing listeners at probe frequencies between 250 and 8000 Hz. The short probe tones were fixed in level (approximately 10-dB SPL). The level of the preceding forward masker was adjusted to obtain masked threshold as a function of the time delay between masker and probe. These isoresponse TMCs were obtained for an on-frequency masker, where the masker frequency (Fm) and probe frequency (Fp) were the same, and for an off-frequency masker below the probe frequency (Fm = 0.6 Fp). Slopes of off-frequency TMCs for probe tones at 250-1000 Hz were steeper than those for probe tones between 2000 and 4000 Hz, supporting the notion that response growth for Fm = 0.6 Fp at lower probe frequencies is not linear. Therefore, a group average off-frequency TMC slope, for probe frequencies between 2 and 4 kHz, was used to calculate response growth at every probe frequency. Input/output response growth curves were derived from the TMCs, and response growth rates were calculated as a function of the masker level in individual ears. At any particular probe frequency, response growth rates varied with input level, from near 1.0 at low input levels, to <0.2 at mid levels, and back to near 1.0 at levels above 80-dB SPL. It was concluded that compression is equally strong at low and high frequencies as it is at mid frequencies.

Audiometry, Pure-Tone↗

PubMed2004

The temporal effect with notched-noise maskers: analysis in terms of input-output functions.

This study examines whether a temporal masking effect may be consistent with a decrease in gain at the masker frequency during the course of the masker. Threshold level of a long-duration notched-noise masker needed to mask a 1- or 4-kHz signal was measured for three conditions: a short-duration signal with a short delay or a long delay from masker onset, and a long-duration signal. The difference between threshold for the long-delay signal and the short-delay signal was defined as the temporal effect. The size of the temporal effect depended on signal frequency, signal level, and masker notch width. Filters estimated from the data had narrower bandwidths for the long-delay condition than for the short-delay condition or the long-duration condition, which seems inconsistent with the hypothesis of a decrease in gain. However, modeling of the data in terms of basilar-membrane input-output functions is consistent with a decrease in gain in the masker frequency region during the course of the masker. For a notch width of 0.0 the results are consistent with a decrease in gain at the signal frequency. For a relative notch width of 0.4, the decrease in gain at the masker frequency may cause a decrease in the suppression of the signal. This decrease in suppression could explain the decrease in filter bandwidth with signal delay.

Adult↗

PubMed2004

Sensitivity to interaural intensitive disparities: listeners' use of potential cues.

Thresholds for interaural intensitive disparities (IIDs) for a 500-Hz tone were measured in several stimulus conditions including those in which the use of intracranial position as a cue was effectively eliminated by roving the interaural temporal disparity of the stimuli. Removing position as a cue resulted in substantial degradation of sensitivity to IID. The overall patterning of the data suggests that threshold-IIDs measured in standard binaural paradigms that yield fused intracranial images reflect the use of changes in intracranial position. That is, comparisons among the data suggest that listeners' judgments depend upon binaural spatial cues and not on comparisons of the concomitant monaural increments and decrements in level, per se, that inevitably result from the imposition of IIDs.

Acoustic Stimulation↗

PubMed2004

External and internal limitations in amplitude-modulation processing.

Three experiments are presented to explore the relative role of "external" signal variability and "internal" resolution limitations of the auditory system in the detection and discrimination of amplitude modulations (AM). In the first experiment, AM-depth discrimination performance was determined using sinusoidally modulated broadband-noise and pure-tone carriers. The AM index, m, of the standard ranged from -28 to -3 dB (expressed as 20 log m). AM-depth discrimination thresholds were found to be a fraction of the AM depth of the standard for standards down to -18 dB, in the case of the pure-tone carrier, and down to -8 dB, in the case of the broadband-noise carrier. For smaller standards, AM-depth discrimination required a fixed increase in AM depth, independent of the AM depth of the standard. In the second experiment, AM-detection thresholds were obtained for signal-modulation frequencies of 4, 16, 64, and 256 Hz, applied to either a band-limited random-noise carrier or a deterministic ("frozen") noise carrier, as a function of carrier bandwidth (8 to 2048 Hz). In general, detection thresholds were higher for the random- than for the frozen-noise carriers. For both carrier types, thresholds followed the pattern expected from frequency-selective processing of the stimulus envelope. The third experiment investigated AM masking at 4, 16, and 64 Hz in the presence of a narrow-band masker modulation. The variability of the masker was changed from entirely frozen to entirely random, while the long-term average envelope power spectrum was held constant. The experiment examined the validity of a long-term average quantity as the decision variable, and the role of memory in experiments with frozen-noise maskers. The empirical results were compared to predictions obtained with two modulation-filterbank models. The predictions revealed that AM-depth discrimination and AM detection are limited by a combination of the external signal variability and an internal "Weber-fraction" noise process.

Acoustic Stimulation↗

PubMed2004

Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds.

Interactions among the multiple channels of a cochlear prosthesis limit the number of channels of information that can be transmitted to the brain. This study explored the influence on channel interactions of electrical pulse rates and temporal offsets between channels. Anesthetized guinea pigs were implanted with 2-channel scala-tympani electrode arrays, and spike activity was recorded from the auditory cortex. Channel interactions were quantified as the reduction of the threshold for pulse-train stimulation of the apical channel by sub-threshold stimulation of the basal channel. Pulse rates were 254 or 4069 pulses per second (pps) per channel. Maximum threshold reductions averaged 9.6 dB when channels were stimulated simultaneously. Among nonsimultaneous conditions, threshold reductions at the 254-pps rate were entirely eliminated by a 1966-micros inter-channel offset. When offsets were only 41 to 123 micros, however, maximum threshold shifts averaged 3.1 dB, which was comparable to the dynamic ranges of cortical neurons in this experimental preparation. Threshold reductions at 4069 pps averaged up to 1.3 dB greater than at 254 pps, which raises some concern in regard to high-pulse-rate speech processors. Thresholds for various paired-pulse stimuli, pulse rates, and pulse-train durations were measured to test possible mechanisms of temporal integration.

Analysis of Variance↗

PubMed2004

The apparent immunity of high-frequency "transposed" stimuli to low-frequency binaural interference.

Discrimination of interaural temporal disparities (ITDs) was measured with either conventional or transposed "targets" centered at 4 kHz. The targets were presented either in the presence or absence of a simultaneously gated diotic noise centered at 500 Hz, the interferer. As expected, the presence of the low-frequency interferer resulted in substantially elevated threshold-ITDs for the conventional high-frequency stimuli. In contrast, these interference effects were absent for ITDs conveyed by the high-frequency transposed targets. The binaural interference effects observed with the conventional high-frequency stimuli were well accounted for, quantitatively, by the model described by Heller and Trahiotis [L. M. Heller and C. Trahiotis, J. Acoust. Soc. Am. 99, 3632-3637 (1996)]. The lack of binaural interference effects observed with the high-frequency transposed stimuli was not predicted by that model. It is suggested that transposed stimuli may be one of a class of stimuli that do not foster an obligatory combination of binaural information between low- and high-frequency regions. Under those conditions that do foster such an obligatory combination, one could still consider models of binaural interference, such as the one described in Heller and Trahiotis, to be valid descriptors of binaural processing.

Acoustic Stimulation↗

PubMed2004

Sequential F0 comparisons between resolved and unresolved harmonics: no evidence for translation noise between two pitch mechanisms.

Carlyon and Shackleton [J. Acoust. Soc. Am. 95, 3541-3554 (1994)] suggested that fundamental-frequency (F0) discrimination performance between resolved and unresolved harmonics is limited by an internal "translation" noise between the outputs of two distinct F0 encoding mechanisms, in addition to the encoding noise associated with each mechanism. To test this hypothesis further, F0 difference limens (DLF0s) were measured in six normal-hearing listeners using sequentially presented groups of harmonics. The two groups of harmonics presented on each trial were bandpass filtered into the same or different spectral regions, in such a way that both groups contained mainly resolved harmonics, both groups contained only unresolved harmonics, or one group contained mainly resolved and the other only unresolved harmonics. Three spectral regions (low: 600-1150 Hz, mid: 1400-2500 Hz, or high: 3000-5250 Hz) and two nominal F0s (100 and 200 Hz) were used. The DLF0s measured in across-region conditions were well accounted for by a model assuming only two sources of internal noise: the encoding noise estimated on the basis of the within-region results plus a constant noise associated with F0 comparisons across different spectral regions, independent of resolvability. No evidence for an across-pitch-mechanism translation noise was found. A reexamination of previous evidence for the existence of such noise suggests that the present negative outcome is unlikely to be explained by insufficient measurement sensitivity or an unusually large across-region comparison noise in the present study. While the results do not rule out the possibility of two separate pitch mechanisms, they indicate that the F0s of sequentially presented resolved and unresolved harmonics can be compared internally at no or negligible extra cost.

Acoustic Stimulation↗

PubMed2005

Sensitivity of a tucuxi (Sotalia fluviatilis guianensis) to airborne sound.

Auditory systems of cetaceans are considered highly specialized for underwater sound processing, whereas the extent of their hearing capacity in air is still a point of issue. In this study, the sensitivity to airborne sound in a male tucuxi (Sotalia fluviatilis guianensis) was tested by means of a go/no go response paradigm. Auditory thresholds were obtained from 2 to 31.5 kHz. Compared to the hearing thresholds of other dolphins as well as of amphibian mammals, the sensitivity to airborne sound of the test subject is low from 2 to 8 kHz, with the highest threshold at 4 kHz. Thresholds at 16 and 31.5 kHz reveal a sharp increase in hearing sensitivity. Thus, although not obtained in this study, the upper aerial hearing limit is in the ultrasonic range. A comparison of the present data with the underwater audiogram of the same test subject referred to sound intensity indicates that the sensitivity of Sotalia to underwater sound is generally better than to airborne sound.

Air↗

PubMed2005

Level dependence of distortion-product otoacoustic emissions measured at high frequencies in humans.

Given that high-frequency hearing is most vulnerable to cochlear pathology, it is important to characterize distortion-product otoacoustic emissions (DPOAEs) measured with higher-frequency stimuli in order to utilize these measures in clinical applications. The purpose of this study was to explore the dependence of DPOAE amplitude on the levels of the evoking stimuli at frequencies greater than 8 kHz, and make comparisons with those data that have been extensively measured with lower-frequency stimuli. To accomplish this, DPOAE amplitudes were measured at six different f2 frequencies (2, 5, 10, 12, 14, and 16 kHz), with a frequency ratio (f2/f1) of 1.2, at five fixed levels (30 to 70 dB SPL) of one primary (either f1 or f2), while the other primary was varied in level (30 to 70 dB SPL). Generally, the level separation between the two primary tones (L1 > L2) generating the largest DPOAE amplitude (referred to as the "optimal level separation") decreased as the level of the fixed primary increased. Additionally, the optimal level separation was frequency dependent, especially at the lower fixed primary tone levels ( < or = 50 dB SPL). In agreement with previous studies, the DPOAE level exhibited greater dependence on L1 than on L2.

Adult↗

PubMed1974