Masker Bursts Research Articles

Steep temporal integration for tone detection in a multi-tone, random-frequency masker.

In the detection of a tone burst, masking by several tones with random frequencies can produce steep temporal integration. This feature was evaluated for nine normal-hearing adults for 1000-Hz tone bursts presented in a continuous train of four-tone masker bursts. Masker frequencies were randomly selected (250-4000 Hz) for each burst, with the proviso that all tones were separated by ≥0.2 oct. Bursts were 80-ms in duration; when present, signal bursts were gated synchronously with masker bursts. The observed mean temporal-integration function was exceptionally steep-thresholds improved by 26 dB as signal duration increased from 1 to 8 bursts. The results also showed that the individual differences were large, and that the mean psychometric function was exceptionally shallow, spanning a range of 35 dB between 0.6 and 0.9 proportion correct responses, consistent with previous reports. These findings were interpreted in the context of three signal-detection models, one based on the absolute-level cue, and two based on the relative-level cue via template matching; all cues were derived from the excitation patterns of the stimuli. Template-matching models were able to predict the shallow psychometric functions as observed, but all models fall short in the steepness of the observed temporal integration.

The role of lateralization in release from informational masking

This study tested whether target and masker must create different spatial percepts, in this case intracranial percepts created under headphones, to achieve spatial release from informational masking. Signals were sequences of 40-ms broadband noise bursts with four target bursts interspersed within a longer train of masker bursts. From a baseline sequence in which target bursts were 400 ms apart, either the second or third burst was advanced by 80 ms to create two different temporal patterns that subjects discriminated. Target bursts were intermixed among masker bursts such that pattern identification was at chance when all bursts were diotic, but near perfect when target and masker bursts were delivered with moderate interaural differences of opposite sign. Performance in these unprocessed conditions was compared to that obtained when stimuli were processed by an algorithm that swapped interaural differences in alternating frequency bands [S. Sheffield et al., J. Acoust. Soc. Am. 145, 1129–1142 (2019)], thereby degrading lateralization but preserving the magnitudes of interaural differences. Early results show substantially reduced masking release in degraded lateralization conditions, despite their preservation of interaural differences, suggesting a prominent role for perceived target-masker separation in spatial release from informational masking. [Work supported by NIDCD R01 01625.]

Effects of temporal coherence and signal-frequency uncertainty for tone detection in a random-frequency multi-tonal masker

Detection thresholds tend to be lower when the spectral and/or temporal characteristics of the signal are predictable than unpredictable, particularly in an unpredictable masker. The present study evaluated the detrimental effect of frequency uncertainty and the beneficial effect of temporal coherence for a pure-tone signal presented in a multi-tonal masker with unpredictable frequency sequences. Stimuli were composed of 80-ms tone bursts. The signal was 1, 2, 4, or 8 sequential tone bursts, and burst frequency was either fixed across trials or randomly varied across trials but fixed across bursts. The masker was composed of four streams of tone bursts; the frequency of each burst was randomly drawn from a uniform distribution 250-4000 Hz, with the caveat that synchronous masker and signal bursts were separated by 1/5 oct or more. Signal and masker bursts were synchronously gated, and the masker played continuously throughout a threshold estimation track. Thresholds tended to improve with increasing numbers of signal bursts and worsen with increasing signal frequency uncertainty. These factors appeared to interact; signal frequency uncertainty was less detrimental when the signal was composed of larger numbers of bursts. Preliminary models of detection will be discussed.

Spatial consistency as a cue for segregation and localization

Many real-world auditory scenes are dynamic and complex, with multiple sounds that may change location over time. In this experiment, we examined the ability of listeners to localize a spatially consistent target sound in a dynamic, spatially varying auditory scene. The target and masker stimuli were composed of sequences of 60-ms bursts of uncorrelated noise (2 to 16 bursts in duration) and differed only in their degree of spatial consistency. Specifically, each target burst within a sequence came from the same spatial location (which varied from trial to trial), whereas each masker burst within a sequence came from a different, randomly chosen spatial location. The listener’s task was to localize the spatially-consistent sequence. Localization errors decreased by approximately 11° with each doubling of the sequence duration, and approached quiet performance with 16-burst sequences. Adding a second masker increased localization errors by approximately 14° overall. These results suggest that spatial information can be combined across multiple observations over time to identify and localize a spatially consistent target in a dynamic auditory scene. These data will be discussed in terms of the information obtained from each burst and the manner in which the information is combined across bursts.

Erratum: “The effect of signal-temporal uncertainty on detection in bursts of noise or a random-frequency complex” [J. Acoust. Soc. Am. 124(5), EL321–EL327 (2008)

Several programming errors were discovered subsequent to publication. These errors were the authors' mistake and resulted in discrepancies between the reported and actual duration of stimuli and the timing of stimulus presentations. The signal was 125 ms, including a 5-ms, linear onset/offset ramps. Each masker burst was 125 ms in duration, including a 5-ms, linear onset/offset ramps. One masker component was selected from the uniform distribution of 300 to 920 Hz and the other component from the distribution of 1080 to 3100 Hz. A 5-ms period of silence occurred after each burst of the continuous masker. When a signal was present, it was played 80 ms after the onset of the fourth masker burst, from when the trial was initiated. Results from three trained listeners, who were not in the original data set, indicate that these programming errors did not change the size of the effect of signal-temporal uncertainty in the broadband noise condition for any of the listeners nor in the random-frequency, two-tone masker condition for one of the listeners. In the latter condition, the effect size was 4 and 6 dB larger for two of the listeners when the errors were corrected compared to when they were not.

The relationship between MOC reflex and masked threshold

Otoacoustic emission (OAE) amplitude can be reduced by acoustic stimulation. This effect is produced by the medial olivocochlear (MOC) reflex. Past studies have shown that the MOC reflex is related to listening in noise and attention. In the present study, the relationship between strength of the contralateral MOC reflex and masked threshold was investigated in 19 adults. Detection thresholds were determined for 1000-Hz, 300-ms tone presented simultaneously with one repetition of a 300-ms masker in an ongoing train of masker bursts. Three masking conditions were tested: 1) broadband noise 2) a fixed-frequency 4-tone complex masker and 3) a random-frequency 4-tone complex masker. Broadband noise was expected to produce energetic masking and the tonal maskers were expected to produce informational masking in some listeners. DPOAEs were recorded at fine frequency intervals from 500 to 4000 Hz, with and without contralateral acoustic stimulation. MOC reflex strength was estimated as a reduction in baseline level and a shift in frequency of DPOAE fine-structure maxima near 1000-Hz. MOC reflex and psychophysical testing were completed in separate sessions. Individuals with poorer thresholds in broadband noise and in random-frequency maskers were found to have stronger MOC reflexes.

Effect of signal-temporal uncertainty during childhood: Detection of a tonal signal in a random-frequency, two-tone masker.

The purpose of this study was to determine if listeners benefit from a cue indicating when in time a signal occurs. In order to examine age-related differences in performance, three groups of children (5–7, 8–10, and 11–13 year-olds) and adults were tested. Thresholds were measured for a 120-ms, 1000-Hz signal presented in a continuous random-frequency, two-tone masker presented at 50 dB SPL. Each 120-ms masker burst was composed of a pair of tones, one selected from a uniform distribution 300–920 Hz and the other from 1080–3000 Hz. This masker was selected because it is expected to produce primarily informational masking. Listeners completed two temporal conditions: (1) temporally-defined, with the signal embedded in a 600-ms light cue and (2) temporally-uncertain, with no light cue. Two phases of testing were completed for each temporal condition. For phase 1, a single-interval, adaptive track procedure determined the midpoint of the psychometric function. In phase 2, signal levels around the midpoint were tested using a single-interval method of constant stimuli procedure. For both temporal conditions, listeners completed four runs of 40 trials, with an equal signal-nonsignal probability. Results indicate a substantial release from masking with reduced signal-temporal uncertainty for both children and adults.

Temporal effects with multiple-burst multitone masking.

Previous work has shown that the detection threshold for a tone-burst target presented simultaneously with a randomized multitone masker that is not affected by increasing the number of identical target-plus-masker bursts. However, when the masker burst is repeated, but the target tone is presented only in alternate bursts, masked detection thresholds may be reduced significantly [Kidd et al., (1994). J. Acoust. Soc. Am. 95(6), 3475–3480]. In the present study, similar conditions were tested, but the masker-alone bursts were presented either ipsilateral or contralateral to the target-plus-masker bursts. In addition, the detectability of a single target burst was measured when the target-plus-masker burst was either preceded or followed by masker-alone bursts. As is typical with random multitone maskers, there were large threshold differences between listeners, but ipsilateral presentation of the alternate masker-alone bursts provided greater benefit than contralateral presentation. Furthermore, some listeners showed no improvement of single-burst detection thresholds with either pre- or postcursors, while others showed a sizable improvement that was similar for both pre- and postcursors. Discussion will focus on possible mechanisms underlying these temporal informational masking effects.

Release from informational masking in children: Effect of multiple signal bursts

This study examined the degree to which increasing the number of signal presentations provides children with a release from informational masking. Listeners were younger children (5-7 years), older children (8-10 years), and adults. Detection thresholds were measured for a sequence of repeating 50-ms bursts of a 1000-Hz pure-tone signal embedded in a sequence of 10- and 50-ms bursts of a random-frequency, two-tone masker. Masker bursts were played at an overall level of 60-dB sound pressure level in each interval of a two-interval, forced choice adaptive procedure. Performance was examined for conditions with two, four, five, and six signal bursts. Regardless of the number of signal bursts, thresholds for most children were higher than thresholds for most adults. Despite developmental effects in informational masking, however, masked threshold decreased with additional signal bursts by a similar amount for younger children, older children, and adults. The magnitude of masking release for both groups of children and for adults was inconsistent with absolute energy detection. Instead, increasing the number of signal bursts appears to aid children in the perceptual segregation of the fixed-frequency signal from the random-frequency masker as has been previously reported for adults [Kidd, G., et al. (2003). J. Acoust. Soc. Am. 114, 2835-2845].

Informational masking release in children and adults

This study assessed informational masking and utilization of cues to reduce that masking in children aged 4-9 years and in adults. The signal was a train of eight consecutive tone bursts, each at 1 kHz and 60 ms in duration. Maskers were comprised of a pair of synchronous tone-burst trains, with randomly chosen frequencies spanning 200-5000 Hz, with a protected region 851-1175 Hz. In the reference condition, maskers were eight bursts in duration, with a fixed frequency within intervals. Experiment 1 tested two monotic masking release conditions: within-interval randomization of masker burst frequency and the introduction of leading masker bursts. Experiment 2 examined masking release in which the signal was presented to one ear and masking components were presented to both ears (masker components in the contralateral ear were 10 dB higher than those in the ipsilateral ear). Both adults and children demonstrated a significant informational masking effect, with children showing a larger effect on average. Both groups also showed significant release from masking in the two monotic conditions, although children received somewhat less benefit from the masking release cues. The binaural condition supported a moderate release from informational masking in adults, but resulted in increased informational masking in children.

An examination of temporal signal uncertainty for sequences of noise or random-frequency maskers

The effect of temporal uncertainty was examined on detection of a 1000-Hz tone presented simultaneously with one of a sequence of five masker bursts, using a 2-AFC, adaptive procedure. The signal and each masker burst were 100-ms (10-ms rise/fall), with no temporal overlap between masker bursts. Each masker burst was 60 dB SPL. Across conditions, maskers were broadband-noise (300–3000 Hz) or random-frequency multi-tonal maskers with 1, 2, or 10 components. Components for the random-frequency maskers were drawn from 300 to 3000 Hz, excluding a 160-Hz band around the signal. Thresholds for conditions with no temporal uncertainty (signal presented with the first, third, or fifth masker burst on all trials) were compared to performance with maximal temporal uncertainty (signal position varied on every trial). There was no effect of temporal uncertainty for the noise masker. For random-frequency maskers, performance was uniformly poor for both fixed- and random-position signals, except for some release from masking for signals presented with the last masker burst. For three of four listeners, even 1-component maskers showed large amounts of masking in all conditions. These results suggest that the effects of temporal uncertainty are minimal for these stimuli. [Work supported by NIDCD.]

Effect of signal frequency uncertainty for random multi-burst maskers

The detectability of a sequence of equal-frequency tone pips masked by random multi-burst complexes may depend on the perceptual segregation of the signal stream from the random masker. If so, detection thresholds may be independent of whether the signal frequency is known versus uncertain. In this experiment observers detected a signal stream of 8 sequential equal-frequency 30 ms tone pips embedded in a random masker composed of 8 sequential bursts. A yes/no procedure was used, and the independent variable p (probability a tone was played at a particular time-by-frequency location) governed the number of masker tones in each burst. The dependent variable was d. Threshold values of p were obtained for signal streams at 5 different frequencies. Sensitivity was superior for the mid-frequency signal, and decreased as the signal frequencies approached the edge of the frequencies the masker tones occupied (200–5000 Hz). When the frequency of the signal stream was randomly varied from trial to trial, sensitivity was poorer than for any of the fixed-frequency signals. Thus, the detectability of a sequence of tone pips is reduced when the signal frequency is uncertain compared to certain. Additionally, sensitivity increased when the signal stream was delayed relative to the masker bursts.

Monaural informational masking release in children and adults

Informational masking refers to an elevation in signal threshold due to stimulus uncertainty, rather than to energetic masking. This study assessed informational masking and utilization of cues to reduce that masking in children aged 5–9 and adults. We used a manipulation introduced by Kidd et al. [J. Acoust. Soc. Am. 95, 3475–3480 (1994)] in which the signal was a train of eight consecutive tone bursts, each at 1 kHz and 60 ms in duration. Maskers were comprised of a pair of synchronous tone-burst trains whose frequencies were selected from the range spanning 0.2–5 kHz, with a protected region 851–1175 Hz. In the reference condition, where informational masking is pronounced, these maskers were eight bursts and had a fixed frequency within each interval, with new frequencies chosen randomly prior to each interval. Two conditions of masking release were tested: random frequency selection for each masker burst and a masker leading fringe of two additional 60-ms bursts. Both children and adults showed a significant informational masking effect, with children showing a larger effect. Both groups also showed significant release from masking, though initial results suggest that this may have been reduced in the youngest children. [Work supported by NIH, RO1 DC00397.]

Multiple bursts, multiple looks, and stream coherence in the release from informational masking.

In the simultaneous multitone masking paradigm introduced by Neff and Green [Percept. Psychophys. 41, 409-415 (1987)] the masker typically is a small number of tones having frequencies and levels that are randomly drawn on every presentation. Large amounts of masking for a pure-tone signal often occur that are thought to reflect central, rather than peripheral, limitations on processing. Previous work from this laboratory has indicated that playing a rapid succession of randomly drawn multitone maskers in each observation interval dramatically reduces the amount of masking that is observed relative to a single burst (SB). In this multiple-bursts-different (MBD) procedure, the signal tone is the only constant frequency component during the sequence of bursts and tends to perceptually segregate from the masker. In this study, the number of masker bursts and the interburst interval (IBI) were varied. The goals were to determine how the release from masking relative to the SB condition depends on the number of bursts and to examine whether increasing the IBI would cause each burst to be processed independently. If the latter were true, it might disrupt the perception of signal stream coherence, thereby diminishing the MBD advantage. However, multiple independent looks could also lead to an improvement in performance. For those subjects showing large amounts of informational masking in the SB condition, substantial reduction in masked thresholds occurred as the number of masker bursts increased, while masking increased as IBI lengthened. The results were not consistent with a simple version of a multiple-look model in which the information from each burst was combined optimally, but instead appear to be attributable to mechanisms involved in the perceptual organization of sounds.

Informational masking in listeners with sensorineural hearing loss.

Measures of energetic and informational masking were obtained from 46 listeners with sensorineural hearing loss. The task was to detect the presence of a sequence of eight contiguous 60-ms bursts of a pure tone embedded in masker bursts that were played synchronously with the signal. The masker was either a sequence of Gaussian noise bursts (energetic masker) or a sequence of random-frequency 2-tone bursts (informational masker). The 2-tone maskers were of two types: one type that normally tends to produce large amounts of informational masking and a second type that normally tends to produce very little informational masking. The two informational maskers are called "multiple-bursts same" (MBS), because the same frequency components are present in each burst of a sequence, and "multiple-bursts different" (MBD), because different frequency components are presented in each burst of a sequence. The difference in masking observed for these two maskers is thought to occur because the signal perceptually segregates from the masker in the MBD condition but fuses with the masker in MBS. In the present study, the effectiveness of the MBD masker, measured as the signal-to-masker ratio at masked threshold, increased with increasing hearing loss. In contrast, the signal-to-masker ratio at masked threshold for the MBS masker changed much less as a function of hearing loss. These results suggest that sensorineural hearing loss interferes with the ability of the listener to perceptually segregate individual components of complex sounds. The results from the energetic masking condition, which included critical ratio estimates for all listeners and auditory filter characteristics for a subset of the listeners, indicated that increasing hearing loss also reduced frequency selectivity at the signal frequency. Overall, these results suggest that the increased susceptibility to masking observed in listeners with sensorineural hearing loss is a consequence of both peripheral and central processes.

Measurements of peripheral compression using forward masking and pulsation threshold

Development of a reliable psychophysical measure of the basilar-membrane (BM) response function is of great importance, not least as a diagnostic tool for sensorineural hearing loss. Described here are attempts to estimate the response function using forward masking and pulsation threshold. Both techniques measure, in effect, the masker level needed to mask a higher frequency signal as a function of signal level. In the forward-masking design, the signal is a 4-ms tone burst presented 2 ms afer a 100-ms masker. In the pulsation-threshold design, 200-ms signal bursts are alternated with 200-ms masker bursts and the listener determines the masker level at which the signal just begins to sound ‘‘continuous’’ as opposed to ‘‘pulsed.’’ This is assumed to occur when the masker and signal excitation levels are equal at the BM place tuned to the signal. The experiemnts are based on the finding that the BM response function is roughly linear for stimuli with frequencies well below characteristic frequency (CF). A plot of masker level at threshold against signal level provides, therefore, an estimate of the BM response to the (CF) signal. Results from normal and impaired listeners will be presented and the relative merits of the techniques discussed.

Informational masking in the identification of simple auditory patterns

Listeners identified six auditory patterns comprised of eight sequential tone bursts [cf. Kidd et al., 2916(A) (1994)]. Several factors affecting performance were examined including center frequency, level and the size of the frequency steps forming the patterns. In masked conditions, a multitone masker was played synchronously with each pattern element. The components of the multitone masker were chosen randomly on every burst within a presentation interval. Masker components were excluded from a region of 20% of the pattern center frequency to minimize ‘‘energetic masking.’’ The results in quiet indicated that identification performance was nearly perfect for pattern frequency steps as small as 1% and at levels as low as 20 dB SL. Considerable ‘‘informational masking’’ was produced by the random multitone masker bursts. The masked identification‐level functions were shallow, rising on average about 2% per dB. Several signal and masker presentation schemes were examined that were intended to reduce the observed masking. To date, the most effective means for improving signal pattern identification has been to present the signal to one ear and identical maskers to both ears with the masker leading in time (8 ms) in the ear contralateral to the signal. [Work supported by NIH.]

Reducing informational masking by sound segregation

Informational masking was reduced using three stimulus presentation schemes that were intended to perceptually segregate the signal from the masker. The maskers were sets of sinusoids chosen randomly in frequency and intensity on each stimulus interval or, in some conditions, on every masker burst in a series of bursts within intervals. Masker components were excluded from the frequency region surrounding the 1000-Hz signal to minimize the energetic masking. Masked thresholds as great as 60-70 dB above quiet threshold were observed for some subjects in some conditions. It was shown that this informational masking could be reduced as much as 40 dB by: (1) presenting the masker to both ears and signal to one ear; (2) playing different masker samples sequentially in each interval of every trial; or (3) presenting the signal in alternate bursts of multiple, identical masker samples. For the binaural manipulation, informational masking was reduced because the masker and signal were perceived as originating from different interaural locations. In the latter two manipulations, a difference in the spectral or temporal pattern of the signal and masker provided the detection cue. These effects were interpreted as evidence of the importance of perceptual segregation of sounds in noisy listening environments where signal reception is not limited by energetic masking.

The effect of masker spectral asymmetry on overshoot in simultaneous masking

"Overshoot" is a simultaneous masking phenomenon: Thresholds for short high-frequency tone bursts presented shortly after the onset of a broadband masker are raised compared to thresholds in the presence of a continuous masker. Overshoot for 2-ms bursts of a 5000-Hz test tone is described for four subjects as a function of the spectral composition and level of the masker. First, it was verified that overshoot is largely independent of masker duration. Second, overshoot was determined for a variety of 10-ms masker bursts composed of differently filtered uniform masking noise with an overall level of 60 dB SPL: unfiltered, high-pass (cutoff at 3700 Hz), low-pass (cutoff at 5700 Hz), and third-octave-band-(centered at 5000 Hz) filtered uniform masking noises presented separately or combined with different bandpass maskers (5700-16000 Hz, 5700-9500 Hz, 8400-16000 Hz) were used. Third, masked thresholds were measured for maskers composed of an upper or lower octave band adjacent to the third-octave-band masker as a function of the level of the octave band. All maskers containing components above the critical band of the test tone led to overshoot; no additional overshoot was produced by masker components below it. Typical values of overshoot were on the order of 12 dB. Overshoot saturated when masker levels were above 60 dB SPL for the upper octave-band masker. The standard neurophysiological explanation of overshoot accounts only partially for these data. Details that must be accommodated by any full explanation of overshoot are discussed.

A forced-choice paradigm for pulsation-threshold measurements

A 2I-2AFC paradigm for pulsation-threshold measurements is described and compared to the conventional method of adjustment. A pulsation-threshold stimulus consisting of four bursts of a masker in rapid temporal alternation with three bursts of a target was presented during one interval of each trial in the forced-choice experiments. The stimulus in the other interval was similar, except that the target remained on during the second and third masker bursts. As target-to-masker ratio decreased the pulsed targets sounded more continuous, and became difficult to discriminate from the continuously presented targets. Pulsation thresholds were measured using various monaural and binaural targets and maskers. The difference between thresholds obtained using the forced-choice and adjustment procedures depended on whether tonal or broadband maskers were used. However, the dependence of these thresholds on masker parameters such as frequency, intensity, and interaural phase were similar for the two procedures. It appears that variability in pulsation thresholds due to subjective criterion fluctuations using the method of adjustment can be eliminated by use of the forced-choice paradigm. [Supported by NIH.]