Biomedical subjects

N F Viemeister

Publications and source records attributed to N F Viemeister.

At least 19 recordsLinked to original sources

PubMed1995

Intensity discrimination under forward and backward masking: role of referential coding.

The present experiments investigated the hypothesis that listeners can code intensity by reference to proximal stimuli in order to improve intensity discrimination performance in conditions of nonsimultaneous masking. The experiments used 30-ms tone bursts as the masker, pedestal, and "proximal burst." The masker level was 80 dB, the pedestal level was 50 dB. In the first experiment the silent interval between the masker and the pedestal was varied. Surprisingly, in both forward and backward masking situations, the Weber fraction decreased as the silent interval was decreased from 100 to 12.5 ms. This is consistent with the referential coding hypothesis: At short intervals performance improves because the level of the pedestal is coded by reference to the proximal masker. In a further set of experiments, the silent interval was 100 ms and an additional proximal burst was presented either 12.5 ms before or 12.5 ms after the pedestal. The proximal burst produced a substantial decrease in the Weber fraction, but only when it was close in frequency to the pedestal, and with a higher intensity. The results are consistent with the auditory system having the ability to produce a robust intensity measure by reference to proximal signals. These findings also provide further evidence that the mid-level elevation in forward masking is not solely the result of processes operating at the level of the auditory nerve.

Auditory Perception↗

PubMed1994

Intensity discrimination in normal-hearing and hearing-impaired listeners.

Weber fractions (delta I/I) for gated 500-ms tones at 0.3, 0.5, 1, 2, and 3 kHz, and at levels of the standard ranging from absolute threshold to 97 dB SPL, were measured in quiet and in high-pass noise in five listeners with cochlear hearing loss and in three normal-hearing listeners. In regions of hearing loss, the Weber fractions at a given SPL were sometimes normal. When the Weber fractions were normal or near-normal, the addition of high-pass noise elevated the Weber fraction, strongly suggesting the use of spread of excitation to higher frequencies. Inversely, when the Weber fractions were elevated, the addition of high-pass noise produced no additional elevation, suggesting an inability to use spread of excitation. In general, the relative size of the Weber fractions, the effects of high-pass noise, and to a lesser extent, the dependence of the Weber fraction on level, were consistent with expectations based upon the audiometric configuration and the use of excitation spread. There were several notable inconsistencies, however, in which normal Weber fractions were seen at a frequency on the edge of a steep high-frequency loss, and in which elevated Weber fractions were observed in a flat audiometric configuration. Finally, when compared at the same SL, the Weber fraction was sometimes smaller in cochlear-impaired than in normal hearing listeners. This was true even in high-pass noise, where excitation spread was limited, and may reflect the unusually steep rate versus level functions seen in auditory nerve fibers that innervate regions of pathology.

Auditory Perception↗

PubMed1994

Frequency modulation versus amplitude modulation discrimination: evidence for a second frequency modulation encoding mechanism.

The encoding mechanisms for amplitude modulation (AM) and frequency modulation (FM) were investigated using AM-FM discrimination tasks. In the first experiment, AM and FM were set at equally detectable levels within a trial, and discrimination thresholds were obtained adaptively in a 3IFC task. Here, AM-FM discrimination thresholds were considerably larger than both AM and FM detection thresholds. This is consistent with an encoding system whereby AM and FM are partially encoded by the same mechanism. In the second experiment, performance on AM-FM discrimination is measured with a fixed-level procedure. Psychometric functions obtained for a constant modulation depth of AM were nonmonotonic with FMs modulation index beta and each displayed a single minimum. The nonmonotonic nature of the functions is consistent with a model in which FM is encoded primarily with the same mechanism that encodes AM but also with a second mechanism, probably related to changes in instantaneous frequency, that is independent of the mechanism that extracts AM. The fact that minima in the discrimination psychometric functions increase from d' = 0 as beta increases indicates that the information encoded by the second mechanism becomes more detectable with increasing beta.

Auditory Perception↗

PubMed1992

Intensity discrimination under backward masking.

The Weber fraction was measured for a 25-ms sinusoidal pedestal presented 100 ms before, or 100 ms after, an intense narrow-band noise. Consistent with the finding of Zeng et al. [Hear. Res. 55, 223-230 (1991)], the forward masker caused an elevation in the Weber fraction at medium pedestal levels. Surprisingly, however, a much larger midlevel elevation was observed in the backward masking conditions; in some cases, the Weber fraction was increased by over 20 dB by the backward masker. In both masking conditions, presenting a notched noise simultaneously with the pedestal reduced the magnitude of the midlevel elevation. These results indicate that it is possible to produce large masking effects on intensity discrimination in conditions where there is no possibility of the masker affecting the representation of the pedestal at the level of the auditory nerve. This suggests that there may be "central" processes underlying the original finding of Zeng et al. Despite the similarities in the results, however, it is not certain that the elevations seen in the forward and backward masking conditions were caused by the same mechanisms.

Acoustic Stimulation↗

PubMed1992

The effects of notched noise on intensity discrimination under forward masking.

Zeng et al. [Hear. Res. 55, 223-230 (1991)] reported that at moderate levels there is an increase in the intensity jnd for 25-ms sinusoidal pedestals presented 100 ms after an intense narrow-band noise. They suggested that this effect is related to the finding that low spontaneous rate (SR) auditory-nerve neurons take a considerable time to recover from adaptation [E. M. Relkin and J. R. Doucet, Hear. Res. 55, 215-222 (1991)]: 100 ms after the noise, the low-SR neurons still have elevated thresholds. Therefore, the intensity of a pedestal falling between the saturation level of the high-SR neurons and the elevated threshold of the low-SR neurons will be poorly represented in neutral firing rates, and the jnd will be high. A problem with this interpretation is that subjects may listen "off frequency." Theoretically, it should always be possible to choose a frequency channel for which the pedestal level is within the dynamic range of the high-SR neurons. In the present study, the experiment of Zeng et al. was replicated but with the pedestal presented in the temporal center of a notched noise to prevent off-frequency listening. Surprisingly, the notched noise substantially decreased the jnd at mid levels, removing or severely reducing the mid-level jnd elevation. This was true for pedestal frequencies of 1 and 6 kHz. It was also found that even if the notched noise was terminated before pedestal onset the jnd elevation was reduced. This suggests that the effect of the notched noise is not due to suppression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Temporal integration and multiple looks.

The decrease in detection and discrimination thresholds with increases in signal duration has often been taken to indicate that a process of relatively long-term temporal integration occurs in hearing. Two experiments are reported that suggest that no such process occurs. The first experiment is similar to the two-pulse experiment reported by Zwislocki [J. Zwislocki, J. Acoust. Soc. Am. 32, 1046-1059 (1960)] in which the threshold in quiet for a pair of brief pulses is measured as a function of the temporal separation between them. Our data indicate that power integration occurs only for separations less than approximately 5 ms. For separations larger than 5-10 ms, thresholds do not change with separation and the pulses appear to be processed independently. In the second experiment, brief 1-kHz tone pulses separated by 100 ms are presented during gaps in a wideband noise. The threshold for a pair of pulses is lower than that for either pulse presented alone, indicating that some type of "integration" occurs. However, the threshold for the pulse pair is not affected by changes in the level of the noise during the interval between the pulses. These data are inconsistent with the classical view of temporal integration that involves long-term integration. They are consistent with the notion that the input is sampled at a fairly high rate and that these samples or "looks" are stored in memory and can be accessed and processed selectively. This multiple-look model can account for the data from the present experiment and also can account for the data on temporal integration for tones and noise.(ABSTRACT TRUNCATED AT 250 WORDS)

Attention↗

PubMed1990

Discrimination of modulation depth of sinusoidal amplitude modulation (SAM) noise.

The detection of sinusoidal amplitude modulation (SAM) provides a lower bound on the degree to which temporal information in the envelope of complex waveforms is encoded by the auditory system. The extent to which changes in the amount of modulation are discriminable provides additional information on the ability of the auditory system to utilize envelope fluctuations. Results from an experiment on the discrimination of modulation depth of broadband noise are presented. Discrimination thresholds, expressed as differences in modulation power, increase monotonically with the modulation depth of the standard, but do not obey Weber's law. The effects of carrier level and of modulation frequency are consistent with those observed in modulation detection: Changes in carrier level have little effect on modulation discrimination; changes in modulation frequency also have little effect except for standards near the modulation detection threshold. The discrimination of modulation depth is consistent with the leaky-integrator model of modulation detection for standards below--10 dB (20 log ms); for standards greater than--10 dB, the leaky integrator predicts better performance than that observed behaviorally.

Attention↗

PubMed1989

Within- versus cross-channel mechanisms in detection of envelope phase disparity.

These experiments were designed to examine the mechanism of detection of phase disparity in the envelopes of two sinusoidally amplitude-modulated (AM) sinusoids. Specifically, they were performed to determine whether detection of envelope phase disparity was consistent with processing within a single channel in which the AM tones were simply added. In the first condition, with an 8-Hz modulation frequency, phase-disparity thresholds increased sharply with an initial increase in separation of the carrier frequencies. They then remained approximately constant when the separation was an octave or above. In the second condition, with carrier pairs of 1 and 2 kHz or 1 and 3.2 kHz and a modulation frequency of 8 Hz, thresholds were little affected as the level of one carrier was decreased relative to the other. With a modulation frequency of 128 Hz, for most subjects there was more of an effect of level disparity on thresholds. In the third condition, when the modulation frequency was 8 Hz, subjects showed relatively constant thresholds whether the signals were presented monotically, dichotically, or dichotically with low- and high-pass noise. Dichotic thresholds were typically higher than monotic when the modulation frequency was 128 Hz. These results suggest that it is not necessary to have information available within a single additive channel to detect envelope phase disparity. In certain circumstances, a comparison across channels may be used to detect such disparities.

Acoustic Stimulation↗

PubMed1988

Intensity coding and the dynamic range problem.

The psychophysical data on intensity discrimination indicate that certain schemes are unlikely as general intensity codes at the level of the auditory nerve and indirectly suggest that the most likely code is one based upon the firing rates of frequency-localized groups of fibers. A detection-theory analysis of a rate-based intensity code indicates that information from very few fibers can, if the information is appropriately combined, account for psychophysical discrimination even at high intensities. This suggests that fibers with similar CFs can code intensity over a wide range and that complex spectra can be represented at the level of the auditory nerve by a rate-CF code over the dynamic range of hearing. The analysis also indicates, however, a substantial discrepancy between the psychophysical data on the dependence of discrimination thresholds on level and the predicted discrimination behavior of a representative population of auditory nerve fibers. Thus, if intensity coding is based on localized firing rate, this fundamental psychophysical behavior does not result solely from peripheral processes.

Differential Threshold↗

PubMed1988

Intensity discrimination, increment detection, and magnitude estimation for 1-kHz tones.

Intensity difference limens (DLs) were measured over a wide intensity range for 200-ms, 1-kHz gated tones and for 200-ms increments in continuous 1-kHz tones. Magnitude estimates also were obtained for the gated tones over a comparable intensity range. The discrimination data are in general agreement with those from earlier studies but they extend them by showing: (1) good discrimination for gated tones over at least a 115-dB dynamic range; (2) a slight increase in the relative DL (delta I/I) as intensity increases above 95 dB SPL; (3) smaller DLs for increments than for gated tones, with the difference approximately independent of intensity; (4) negligible "negative masking" when thresholds are expressed as intensity differences (delta I). For two of the three subjects, magnitude estimates do not conform to a single-exponent power law for suprathreshold intensities. Over the middle range of intensities where a single exponent is appropriate, the value of the exponent is less than 0.1 for all subjects.

Acoustic Stimulation↗

PubMed1988

The relation between loudness and intensity difference limens for tones in quiet and noise backgrounds.

Recent studies of the relation between loudness and intensity difference limens (DLs) suggest that, if two tones of the same frequency are equally loud, they will have equal relative DLs [R. S. Schlauch and C.C. Wier, J. Speech Hear. Res. 30, 13-20 (1987); J.J. Zwislocki and H.N. Jordan, J. Acoust. Soc. Am. 79, 772-780 (1986)]. To test this hypothesis, loudness matches and intensity DLs for a 1000-Hz pure tone in quiet and in a 40-dB SPL spectrum level broadband noise were obtained for four subjects with normal hearing. The DLs were obtained in both gated- and continuous-pedestal conditions. Contrary to previous reports, equally loud tones do not yield equal relative DLs at several midintensities in the gated condition and at many intensities in the continuous condition. While the equal-loudness, equal-relative-DL hypothesis is not supported by the data, the relation between loudness and intensity discrimination appears to be well described by a model reported by Houtsma et al. [J. Acoust. Soc. Am. 68, 807-813 (1980)].

Audiometry, Pure-Tone↗

PubMed1986

Effects of forward and simultaneous masking on intensity discrimination.

Experiments on intensity discrimination determine the size of the smallest detectable increment added to a fixed pedestal. This paper examines the effects of a masker which either precedes the pedestal (forward masking) or is simultaneous with the pedestal. The increment and pedestal were 1-kHz tones masked in forward masking by pure tones and in simultaneous masking by a broadband noise. Simultaneous masking by the broadband noise eliminates the "near miss" to Weber's law, and thus degrades intensity discrimination at high pedestal levels. Forward masking by the pure tone also degrades intensity discrimination, which may, in part, be explained by the elimination of the near miss. However, the effect on intensity discrimination in some cases is greater in forward than in simultaneous masking, suggesting that some additional process (e.g., adaptation) is involved.

Adult↗

PubMed1985

A case study of monaural diplacusis.

A detailed examination of a case of monaural diplacusis is reported. Low-intensity pure tones presented within a certain frequency range do not sound "pure"; instead, the percept is that of "roughness", "multiple tones" or "beats". In addition, an aftertone is heard upon the cessation of certain tones. Psychophysical experiments (e.g., simultaneous masking, best beats and pitch matching) suggest that the monaural diplacusis results from an interaction between the external tone and an internal tone. The internal tone, however, does not appear to be manifest as a spontaneous oto-acoustic emission.

Acoustic Stimulation↗

PubMed1985

Temporal interactions between pure tones and amplitude-modulated noise.

An auditory interaction between the temporal fine structure of a low-frequency tone and the envelope of a high-frequency waveform was observed at very large frequency separations. Thresholds for detection of sinusoidal amplitude modulation of a high-frequency, narrow-band noise were measured as a function of the relative phase between the modulator and a pure tone with the same frequency as the modulator. These "phase functions" were determined at various intensities of the noise and tone for three different modulation frequencies. In general, the phase functions show that low-frequency stimulation has a cyclic effect on the sensitivity to amplitude modulation; over a limited range of relative phases, the modulation threshold is lower than that measured without low-frequency stimulation whereas over a broader range of relative phases, the modulation threshold is much higher. The difference between minimum and maximum modulation thresholds was observed to be as great as 23 dB. Despite this substantial degree of temporal interaction, little, if any, masking by the low-frequency tone of the high-frequency noise was observed.

Acoustic Stimulation↗

PubMed1985

Simultaneous masking by gated and continuous sinusoidal maskers.

Simultaneous masking of a 20-ms, 1-kHz signal was investigated using 50-ms gated and continuous sinusoidal maskers with frequencies below, at, and above 1 kHz. Gated maskers can produce considerably (5-20 dB) more masking than continuous maskers, and this difference does not appear to result from the spread of energy produced by gating either the masker or the signal. For masker frequencies below the signal frequency, this difference in masking is primarily due to the detection of the cubic difference tone in the continuous condition. For masker frequencies at and above the signal frequency, the difference appears to be an important property of masking. Implications of this frequency-dependent effect for measures of frequency selectivity are discussed.

Acoustic Stimulation↗

PubMed1985

The temporal course of simultaneous tone-on-tone masking.

Threshold for a 20-ms, 1-kHz signal was measured as a function of its temporal position within a longer duration gated masker; masker frequencies were below, at, and above 1 kHz. For a masker frequency above the signal frequency, there is a sizable temporal effect: As the onset of the signal is delayed, threshold decreases rapidly but then increases again as the signal approaches masker offset. Similar results can be observed for a masker frequency below the signal frequency, but that temporal effect is due to the detection of the cubic difference tone. The implication of this frequency-dependent temporal effect for measuring psychophysical tuning curves is discussed.

Acoustic Stimulation↗

PubMed1985

Temporal modulation transfer functions in normal-hearing and hearing-impaired listeners.

Modulation thresholds for sinusoidally amplitude-modulated broadband noise were obtained from normal-hearing and sensorineural hearing-impaired listeners as a function of modulation frequency. The resulting temporal modulation transfer functions (TMTFs) indicated that the impaired listeners were generally less sensitive than the normals to amplitude modulation and, unlike previously published data from normal-hearing listeners, TMTFs in the impaired listeners were level dependent: sensitivity to modulation, particularly for modulation frequencies greater than 100 Hz, decreased with decreases in level. TMTFs were also obtained with band-limited noise from the normal-hearing listeners: the noise was low-pass filtered at 1.6 kHz after modulation and was generally presented with a 1.6-kHz high-pass masker. The TMTFs in the low-pass condition were similar to the TMTFs obtained with broadband noise from the impaired listeners, suggesting that the impaired temporal processing in the hearing-impaired listeners is a result of a narrower effective, 'internal' bandwidth. Increment thresholds for continuous broadband and low-pass noise were obtained in conditions similar to those in which TMTFs were obtained. In general, a similar power-law relationship between modulation threshold and increment threshold was found to exist for both the normal-hearing and the hearing-impaired listeners.

Adult↗

PubMed1984

Selective adaptation to linear frequency-modulated sweeps: evidence for direction-specific FM channels?

Psychometric functions were obtained for detection of linear frequency-modulated pure tones which were preceded by either a pure tone or a linear FM pure-tone adaptor. The results of Gardner and Wilson [J. Acoust. Soc. Am. 66, 704-709(1979)] were generally confirmed: Thresholds were larger by about a factor of 1.7 when the adaptor and test sweeps rose in frequency. This increase in threshold corresponds to a change in performance from 75% to 65% correct. As an alternative to feature-selective channels, we propose that this small effect is due to nonsensory factors, specifically, the use of an adaptor-like reference in the "adapted" condition. Performance similar to that obtained in humans is shown by an ideal receiver that uses an inappropriate reference to match the signal in the detection task.

Acoustic Stimulation↗