Robert S. Schlauch

Listening bandwidths and frequency uncertainty in pure‐tone signal detection

The effect of frequency uncertainty on the detection of tonal signals in noise was studied using a modified probe-signal method. Widths of the listening bands used during detection were measured directly, allowing for an analysis that separates the effects of having to monitor multiple independent bands from those due to limited frequency resolution. Uncertainty was varied by beginning each trial with a cue consisting of one, two, or four randomly chosen, simultaneously presented tones. An expected signal, whose frequency matched one of the components in a cue, was presented on a majority of trials. However, on remaining trials, the signal was a probe, which meant that its frequency differed from one of the components in the cue by a constant ratio. Performance as measured in percent correct declined for probes at increasingly distant ratios from the expected values. The results were converted to dB using individual psychometric functions for expected signals and listening bands were fitted using the rounded exponential filter of Patterson et al. [J. Acoust. Soc. Am. 72, 1788-1803 (1982)]. The obtained bandwidths are comparable to those reported using notched-noise maskers, but there is a small but consistent increase in bandwidth with increased numbers of components in the cues. The primary results is that the effects due to uncertainty are well described by a 1-of-M orthogonal band model, which takes into consideration limitations of the detector, including the widths of the listening bands.

Two‐, three‐, and four‐interval forced‐choice staircase procedures: Estimator bias and efficiency

Threshold estimates for multiple-interval forced-choice staircase procedures were studied using computer simulations. A sigmoidal psychometric function shape governed the hypothetical subjects responses in the simulations. Parameters varied included the number of trials, the step size for stimulus level change, and decision rules that targeted 70.7% and 79.4% correct performance. Each threshold estimate was calculated by averaging the stimulus levels at which a reversal a stimulus level direction occurred. The results of the simulations suggest that, as the number of alternatives is increased from 2 to 4, the variability of repeated threshold estimates decreases or remains constant, and the accuracy of the estimator, in most cases, improves. A subset of the simulations was compared with data obtained in a detection-in-noise task. The behavioral data were consistent with the simulation results. Two major conclusions were reached. First, 3- and 4-interval forced-choice (IFC) procedures are more efficient than a 2IFC procedure with a decision rule that targets 70.7% correct performance even when the additional time required to complete 3- and 4IFC trials is considered. Second, the accuracy of 2IFC procedures can be improved by fitting the trial history of a staircase run using probit analysis.

The effects of fundamental frequency contour manipulations on speech intelligibility in background noisea)

Previous studies have documented that speech with flattened or inverted fundamental frequency (F0) contours is less intelligible than speech with natural variations in F0. The purpose of this present study was to further investigate how F0 manipulations affect speech intelligibility in background noise. Speech recognition in noise was measured for sentences having the following F0 contours: unmodified, flattened at the median, natural but exaggerated, inverted, and sinusoidally frequency modulated at rates of 2.5 and 5.0 Hz, rates shown to make vowels more perceptually salient in background noise. Five talkers produced 180 stimulus sentences, with 30 unique sentences per F0 contour condition. Flattening or exaggerating the F0 contour reduced key word recognition performance by 13% relative to the naturally produced speech. Inverting or sinusoidally frequency modulating the F0 contour reduced performance by 23% relative to typically produced speech. These results support the notion that linguistically incorrect or misleading cues have a greater deleterious effect on speech understanding than linguistically neutral cues.

Safety and clinical performance of acoustic reflex tests.

OBJECTIVE Safety and effectiveness of acoustic reflex tests are important issues because these tests are widely applied to screen for retrocochlear pathology. Previous studies have reported moderately high sensitivity and specificity for detection of acoustic neuroma. However, there have been reports of possible iatrogenic hearing loss resulting from acoustic reflex threshold (ART) and decay (ARD) tests. This study assessed safety and clinical performance of ART tests for detection of acoustic neuroma. DESIGN We report a case in which ARD testing resulted in a significant bilateral permanent threshold shift. This case was the impetus for us to investigate the clinical utility of ART and ARD tests. We analyzed sensitivity and specificity of ART, as well as asymmetry in pure-tone thresholds (PTT) for detection of acoustic neuroma in 56 tumor and 108 non-tumor ears. RESULTS AND CONCLUSIONS Sensitivity and specificity were higher for PTT asymmetry than for ART. Ipsilateral ART at 1000 Hz had poor sensitivity and specificity for detection of acoustic neuroma, and involves some potential risk to residual hearing for presentation levels higher than 115 dB SPL. Approximately half of the acoustic neuroma group had ipsilateral ARTs that would require administration of ARD tests at levels exceeding 115 dB SPL. Therefore, we conclude that PTT asymmetry is a more effective test for detection of acoustic neuroma, and involves no risk to residual hearing. Future studies of contralateral reflex threshold and ARD in combination with PTT asymmetry are recommended.

Incidence of Spontaneous Hearing Threshold Shifts during Modern Concert Performances

OBJECTIVES: Concerts have long periods of intense sound with short break intervals. Hearing concerns are well known to performers; concertgoers largely ignore them. Preperformance and postperformance audiograms were compared to assess hearing threshold shifts with and without earplugs. METHODS: A prospective, randomized study in which 29 volunteers attended 3 concerts, encompassing 3 music genres. Audiograms, seating location, sound intensity, and earplug-use data were collected. Data were analyzed to determine frequency test-retest variability. RESULTS: Sound levels averaged 99.8 dBA, and the maximum was 125.6 dBA. Sixty-four percent (9/14) of participants without earplugs showed significant threshold shifts compared with 27% (4/15) of those using earplugs. No significant differences existed between music genres or seating location. CONCLUSIONS: This study showed a high incidence of threshold shifts in unprotected concertgoers. Sound levels exceeded all Occupational Safety and Health Act rules despite standardized sound systems. A significant reduction in threshold shifts was seen with the use of earplugs.

Basilar membrane nonlinearity and loudness

Loudness matching functions for tones for persons with one shifted-threshold ear (hearing loss and noise-shifted thresholds) and one ear within normal limits were used to derive the presumed basilar membrane (BM) input-output (I/O) function in a normal ear. The comparison was made by assuming that the BM I/O function for the ear with the cochlear threshold shift has a slope of one (a linearized cochlea). The function for the normal ear was derived from the loudness matching function based on this assumption. Comparisons were made for archival basilar membrane data [M. A. Ruggero, N. C. Rich, A. Recio, S. S. Narayan, and L. Robles, J. Acoust. Soc. Am. 101, 2151-2163 (1997)] for chinchilla and archival loudness matches for long-duration tones for persons with various degrees of cochlear hearing loss [F. Miskolczy-Fodor, J. Acoust Soc. Am. 32, 486-492 (1960)]. Comparisons were made also between BM I/O functions and ones derived from loudness matches for persons with unilateral hearing loss simulated by broadband noise. The results show a close resemblance between the basilar membrane I/O function and the function derived from loudness matches for long-duration tones, even though the comparison was between human and chinchilla data. As the degree of threshold shift increases from 40 to 80 dB, the derived BM I/O functions become shallower, with slopes for losses of 60 dB or more falling in the range of values reported for physiological data. Additional measures with short-duration tones in noise show that the slope of the loudness function and the slope of the derived basilar membrane I/O function are associated with the behavioral threshold for the tone. The results for long-duration tones suggest a correspondence between BM displacement and loudness perception in cases of recruitment, but the relation between the degree of loss and the amount of BM compression and the relation between signal duration and compression suggests that other factors, such as the neural population response, may play a role.

Perception of changes in loudness

Neuhoff reported that “rising level tones... change (in loudness) more than falling level tones despite having the same actual change in level... indicating that direction of change is an important (and previously unaddressed) factor in the perception of dynamic loudness change”, and speculated that: “In a natural environment this over-estimation could provide a selective advantage, because rising intensity can signal movement of the source towards an organism.” Leaving aside the question of why it may not be as important for survival to detect the movement of a sound source away from an organism, we dispute the assertion that there is no prior evidence about the influence of direction of change on the degree of change in perceived loudness. This evidence does exist and shows, in contrast to the result reported by Neuhoff, that declining signal intensity covers a greater range of loudness than does rising signal intensity.

Forward-masked intensity discrimination: Duration effects and spectral effects

Three experiments were completed to examine the effect of masker duration and spectrum on forward-masked intensity discrimination. Four listeners participated in each experiment. Intensity discrimination was measured in quiet and in the presence of forward maskers using adaptive forced-choice procedures. The standard duration was either short (10 ms) or long (250 ms) in experiment 1 and short (10 ms) in experiment 2. The standard always occurred 100 ms after the offset of the masker. In the first experiment employing 1.0-kHz maskers and standards, a short duration masker (10 ms) produced more masking than a long duration masker (250 ms). A mid-level elevation of the Weber fraction was observed for all conditions. To ensure that the results of experiment 1 were not influenced by off-frequency listening, the second experiment employed a broadband noise masker. As before, a short duration (10 ms) masker produced more masking than a long duration masker (100 ms) and a mid-level elevation of Weber fractions was observed. This outcome is inconsistent with a peripheral sensory effect for which an increase in masker duration should result in a greater amount of adaptation, and, as a consequence more masking. A third experiment employing a broadband noise masker and standard showed the greatest amount of masking for low-level standards, but only when the duration of the masker and standard was short. This result is similar to one seen for a single listener in the first experiment for short duration tonal maskers and standards. For this listener, a second tone presented at 4.133 kHz presented simultaneously with the 1.0 kHz masker reduced significantly the amount of masking for low-level standards, but the mid-level elevation of the Weber fraction remained. Taken together, these results suggest that perceptual similarity plays a role in forward-masked intensity discrimination but does not account entirely for the mid-level elevation of the Weber fraction.

Masker laterality and cueing in forward-masked intensity discrimination

Forward-masked intensity discrimination was measured as a function of level in experiments designed to reveal insights into the mechanism(s) underlying the midlevel elevation of the Weber fraction. The standard and maskers were 1.0-kHz tones that were separated by 100 ms. Performance was measured for listeners with normal hearing using an adaptive procedure. In experiment 1, intensity discrimination was measured in the presence of an ipsilateral masker (80 dB SPL), a contralateral masker (93 dB SPL), and a binaural (dichotic) masker produced by combining the ipsilateral and contralateral maskers. Listeners perceived only the contralateral masker in the binaural-masker condition. The contralateral masker produced a small midlevel elevation of the Weber fraction. The ipsilateral masker and the binaural masker produced a large, midlevel elevation of the Weber fraction. Experiment 2 found that a two-tone masker resulted in a reduction (improvement) in the Weber fraction for some conditions, but the midlevel elevation remained for all subjects in this cue-tone condition. Experiment 3 demonstrated that cross talk could not account for all of the masking observed with contralateral maskers. Taken together, the results suggest that a single complex mechanism or multiple mechanisms may be responsible for the masking seen in these experiments. On the basis of the cueing results, it is concluded that a portion of the masking is due to cognitive factors; however, a sensory mechanism cannot be ruled out for the remaining portion, based on the results of these experiments. Finally, a small but significant amount of masking due to contralateral maskers places the mechanism for this outcome central to the cochlear nucleus.

Threshold Measurement for Patients with Tinnitus: Pulsed or Continuous Tones

This study compared the effectiveness of pulsed tones (200 ms on/200 ms off) and continuous tones (1 to 2 s) for measuring thresholds in patients with tinnitus. Sixty veterans with tonal tinnitus and a history consistent with noise-induced hearing loss participated. Half were assigned to a pulsed-tone group; half were assigned to a continuous-tone group. Air-conduction thresholds were measured twice for each patient in a single session for octave intervals between 250 Hz and 4000 Hz. Results indicated no significant difference between groups for test-retest differences, but overall more presentations were required to measure thresholds with continuous tones than with pulsed tones at 4000 Hz. Moreover, the continuous-tone group had, on average, more false-positive responses than the pulsed-tone group. This study supports the clinical belief that pulsed tones are preferred over continuous tones for measuring thresholds for persons with tinnitus.