Binaural Interference Research Articles

Binaural speech recognition and the Stenger effect.

The present investigation examined the effects of systematically altering the balance between speech presentation levels to the 2 ears of 12 listeners with bilateral asymmetrical sensorineural hearing impairments. Speech-recognition scores for /VCV/ speech stimuli were obtained from each participant in quiet for 9 conditions ranging from monaural poorer ear only to monaural better ear only, with 7 intermediate conditions in which the sound balance between ears was varied in 5-dB steps. High-pass spectral shaping was provided to the poorer ear, and unshaped amplification was provided to the better ear. The results suggested that, as a group, varying the sound level in the better ear within -20 to +10 dB of the centered position did not significantly change the speech recognition for these participants. No evidence of binaural interference was obtained. Findings also showed that in binaural listening situations, the Stenger effect has little influence upon speech-recognition scores. Even when the listeners were unaware of speech being presented to the better ear, their speech-recognition score reflected the better ear's abilities.

Selected aspects of across-frequency processing in binaural hearing

While considering the many contributions of Dr. R. C. Bilger to knowledge concerning auditory processing, it seemed both fitting and appropriate to honor him by discussing research in binaural hearing that is consistent with key aspects of what we perceive to be his style. Accordingly, the presentation will highlight the integration of theory, measurement, and empirical observation in selected aspects of across-frequency processing in binaural hearing. The topics addressed will be: (1) lateralization as a function of bandwidth, center frequency, and interaural time/phase disparities; (2) binaural interference; (3) the incorporation of peripheral compression, rectification, and low-pass filtering in an index that accounts for binaural detection across frequency.

Slope analysis of Auditory Brainstem Responses in children at risk of central auditory processing disorders

The method of slope vectors was used to quantify Auditory Brainstem Responses (ABR) obtained from nine normal children and nine children at risk for central auditory processing disorders (CAPD) with language impairment, for monaural and binaural stimulation conditions. Slopes thus obtained were subjected to K-Means Cluster Analysis. Distinction between the two groups was obtained only for binaural stimulation conditions, wherein all normal children were grouped under cluster 1 with higher slope values and 6 out of 9 CAPD children were grouped under cluster 2 with lower slopes. The results suggest that there may be several subcategories among children who are found to be at risk for CAPD. One of the subcategories may comprise children who exhibit poor ABR morphology, especially during binaural stimulation conditions, which could be due to binaural interference.

Localization interference between free-field signals

With headphones, the perceived lateral position of one frequency band (the target) can be affected by the presence of a second band with different interaural parameters (the interferer). This binaural interference persists despite a stimulus onset asynchrony (SOA) from interferer to target of up to 320 ms [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am. 94, 735–742 (1993)]. The current study presented targets and interferers in anechoic space from pairs of speakers chosen from an array of 12. A visual pointer was used to indicate the perceived location of the target. Localization of a sinusoidally amplitude-modulated (SAM) target (carrier = 500 Hz, modulator = 250 Hz) was unaffected by the presence of an SAM interferer (carrier = 4000 Hz). When the target was the higher frequency, however, there were large individual differences, with some listeners showing interference while others did not. Unlike the studies with headphones, when interference was seen a distractor to target SOA of only 40 ms was sufficient to eliminate the interference. [Work supported by a grant from the NIH, NIDCD 00087.]

Extents of laterality and binaural interference effects

Extents of laterality produced by ongoing interaural time delays (ITDs) within high-frequency sinusoidally amplitude-modulated (SAM) target tones were measured in the presence or absence of a second, spectrally remote, diotic, SAM tone. The spectrally remote SAM tones had recently been shown to reduce sensitivity to ITDs conveyed by a 4-kHz SAM tone in a previous experiment employing the same listeners [L. M. Heller and C. Trahiotis, J. Acoust. Soc. Am. 97, 1808-1816 (1995)]. All SAM tones were 100% modulated at 250 Hz and were presented at 77 dB SPL for a duration of 250 ms. The SAM target tone was centered at 4 kHz and the lower-frequency SAM tones were centered at either 500 Hz, 1 kHz, or 2 kHz. The data indicate that spectrally remote, diotic, SAM tones "pull" the lateral position of a 4-kHz SAM tone toward the midline, even when the 4-kHz SAM tone contains an ITD of up to 400 or 600 microseconds. This means that effects of spectrally remote information are not confined to tasks which require that listeners detect, or discriminate between, threshold amounts of ITD. Analyses revealed that changes in lateral position, as measured by an acoustic pointing task, cannot in and of themselves account for the interference effects found in discrimination tasks with similar stimuli. It was found, however, that Buell and Hafter's [J. Acoust. Soc. Am. 90, 1894-1990 (1991)] weighted-combination model, when augmented to include measures of laterality as well as measures of discriminability, could provide reasonably accurate predictions of the amounts of interference obtained in the discrimination task.

The relationship between binaural fusion and binaural interference

A stimulus-classification paradigm was used to examine the extent to which judgments of the laterality of 753-Hz targets were influenced by distractors of different frequency. On each trial, the target was presented with one of ten different interaural differences as was the distractor. Each test interval was preceded by a diotic presentation of the target alone. During a block of 100 trials, each combination of target-distractor interaural differences was presented once. The relative weights given to the target and the distractor were assessed by the slope of the best linear boundary between left and right responses. Data were collected for conditions in which the cues were interaural differences of level or time. For all conditions for which target and distractor weights were obtained, binaural interference was measured by determining threshold interaural differences for conditions in which the target was presented alone and in the presence of a diotic distractor. For most subjects, greater interference was obtained when the distractor was at a frequency that was given great weight, although the frequencies weighted most heavily for interaural differences of time were not the same as those weighted heavily for interaural differences of level. [Work supported by NIH.]

Binaural interference effects measured with masking-level difference and with ITD- and IID-discrimination paradigms

The results of several studies have demonstrated that the ability to process binaural information within discrete spectral regions may be degraded by the presence of information at other, even remote, spectral loci. This study focused on binaural interference produced by low-frequency noises (centered at 500 Hz) on the processing of interaural disparities within high-frequency bands of noise (centered on 4 kHz). The bandwidths of the interferers and "targets" were either the same (either 100 or 400 Hz) or different (interferer: 100 Hz; target: 400 Hz). Within a single group of listeners, interference was measured with a masking-level difference paradigm (NoSo vs NoS pi), and in ITD- and IID-discrimination tasks. An important feature of the experiments was the utilization, parametrically, in all three tasks, of pulsed and continuous interferers that were either diotic or were interaurally uncorrelated. As reported in previous experiments, the amounts of interference obtained with pulsed interferers were much greater than those obtained with continuous interferers. The present experiment extends that general finding to discrimination of IIDs. In addition, in all three tasks, pulsed, interaurally uncorrelated interferers produced greater amounts of interference than did pulsed, diotic interferers. The patterns of interference effects found across bandwidths and listeners for the four interference conditions (pulsed-diotic, continuous-diotic, pulsed-uncorrelated, and continuous-uncorrelated) in the MLD paradigm were different than those obtained in either the ITD- or IID-discrimination tasks. One factor that may account for the diverging patterns of interference is that the interaural cues produced by adding the S pi signal to the diotic masker fluctuated in magnitude over time. In contrast, the ITDs and IIDs in the discrimination task were static.(ABSTRACT TRUNCATED AT 250 WORDS)

The segregation of SAM 4-kHz targets from SAM 2-kHz distractors on the basis of interaural envelope delay

A stimulus-classification paradigm was used to examine the extent to which judgments of the laterality of 4-kHz targets, sinusoidally amplitude modulated at 200 Hz, were influenced by 2-kHz distractors that were modulated at rates ranging from 50 to 400 Hz. On each trial, the target was presented with one of ten envelope delays (ranging from −250 to +250 μs in 50-μs steps), as was the distractor. Each test interval was preceded by a diotic presentation of the target alone. The duration of the signals was 200 ms. During a block of 100 trials, each combination of target-distractor delay was presented once. The relative salience of the envelope delays carried by the target and the distractor was assessed by the slope of the best linear boundary between left and right responses. Two listeners gave increasing weight to the target as the difference between the target and distractor modulation frequencies increased, but weighed that target and distractor equally when both were modulated at 200 Hz. Two other listeners gave increasing weight to the 2-kHz distractor as modulation frequency increased, as though its relative salience increased with ‘‘number of looks.’’ These data will be compared to measures of binaural interference that have been obtained for similar stimuli. [Work supported by NIH.]

The reduction of binaural interference by the temporal nonoverlap of components

Threshold interaural delays were measured for a single interaurally delayed 753-Hz target component presented against a background of six diotic distractor components (453, 553, 653, 853, 953, and 1053 Hz). In one set of conditions, all components were gated on simultaneously, but 200-ms after their onset the distractors were turned off for 10, 25, 50, 100, or 200 ms, then turned on again for the remainder of the 500-ms listening interval. In a second set of conditions, the target component was present only during the temporal notch in the distractors for notch durations of 50, 100, and 200 ms. Threshold interaural delays were also measured for the target component in isolation at durations of 50, 100, 200, and 500 ms. In both sets of conditions in which the distractors were present, it was observed that a brief isolated presentation of the target reduced threshold interaural differences of time to nearly the level of thresholds for the target presented in total isolation, while thresholds were many times higher when the distractors had no temporal notch. Possible sources of binaural interference are discussed and the evidence supporting each is evaluated.

Lateralization of comodulated bands of noise

Lateralization thresholds were measured in a 2IFC task for two conditions. The 400-ms signal consisted of two high-frequency narrow bands of noise with common interaural delays (cf.=2.55 and 3.35 kHz; bandwidths=50,100,200,400 Hz). In the first condition, the temporal envelopes of the two bands were the same (comodulated) and, in the second condition, they were independent. Results of this experiment showed improvements in lateralization when the bands were comodulated compared to independently modulated bands. In a second experiment, the two noise bands were replaced by two sinusoidally amplitude modulated (SAM) tones (cf.=2.55 and 4 kHz; modulation rate=100 Hz) and lateralization thresholds were measured as a function of the relative phase of modulation between the two SAMs. Thresholds were lowest when the envelope of the two SAMs were in phase and monotonically increased as the envelopes were increasingly shifted out of phase up to 180°. In a third experiment, binaural interference was examined. Results are discussed in terms of cross-correlation models of binaural hearing. [Work supported by NIH and AFOSR.]

Binaural interference and grouping

The threshold interaural time difference (ITD) of a target tone increases in the presence of spectrally remote distractor tones [e.g., R. H. Dye, J. Acoust. Soc. Am. 88, 2159–2170 (1990)]. It has been suggested that this is because ITD information is grouped across both target and distractor components [e.g., T. N. Buell and E. R. Hafter, J. Acoust. Soc. Am. 90, 1894–1900 (1991)]. If this is so, then the lateralization of the target should be shifted towards the lateralization of the distractor. Alternatively, the presence of a distractor could introduce extra discrimination noise, causing threshold ITDs to rise, but without affecting the target lateralization. Subjects reported whether a target tone presented with a variety of ITDs was perceived to the left or right of midline when a distractor tone was either not present, presented diotically, or presented with a supra-threshold ITD. The slope of the function relating the percentage of leftward responses to the ITD of the target decreased when a distractor was present (indicating a higher threshold). The functions were also shifted horizontally towards the ITD of the distractor. These results suggest that binaural interference results from grouping target and distractor components together. [Work supported by The Wellcome Trust.]

Spectral interference in a binaural detection task: Effects of masker bandwidth and temporal fringea)

Recently, it was reported that the detectability of a 100-ms, 800-Hz tone (the target) presented antiphasically (S pi) against a background of continuous, broadband, diotic noise could be degraded if a 400-Hz tone (the interferer) was gated simultaneously with the target [L. R. Bernstein, J. Acoust. Soc Am. 89, 1306-1313 (1991)]. This degradation, termed "interference," was reduced by presenting the interferer continuously. In the present study, the amount of such interference was measured when the target was masked by either a broadband or a narrow-band (100-Hz-wide) noise. The narrow-band noise produced a relatively large masking-level difference, thereby allowing about 10 dB of interference to be observed. In other conditions, the interferer was turned on (temporally "fringed") prior to the target. The presence and duration of a forward fringe of the interferer did not reduce the interference, even for forward fringes of 320 ms. This result is consistent with those of Woods and Colburn [W. S. Woods and H. S. Colburn, J. Acoust Soc. Am. 91, 2894-2902 (1992)] who measured the detectability of interaural delay of low-frequency tones. The data from both studies indicate that binaural interference is observed even under conditions where interferers and targets are perceptually segregated in the sense that listeners hear more than one sound object.

Detection of interaural differences of level in multitone complexes

This study examined the effects of diotic components on the ability to detect interaural differences of level (IDL) at the center frequency (753 Hz) of a multitone complex. Threshold interaural differences of level (ΔIDL) were measured as a function of the number of components in the complex (3 and 7) and the frequency spacing (Δf) between components (10, 25, 50, 100, and 200 Hz). A 2IFC procedure was used, with the first interval always presenting a diotic complex and the second presenting either a diotic complex or one containing an IDL at 753 Hz. The left channel was incremented and the right decremented so that intracranial images were lateralized to the left. The starting phases of components were randomized between intervals. IDLs were expressed as the level difference at the target frequency. When compared to ΔIDLs obtained for 753 Hz in isolation, the effect of adding diotic components was to increase thresholds. Oddly, ΔIDLs were smallest at Δf = 10 Hz and increased to 7–9 dB at wider Δf's for both three- and seven-component signals. The data at wider Δf's are consistent with binaural interference effects that have been reported for detection of interaural delays. One explanation for the good performance at small Δf's is detection based on the decorrelation of the waveforms at the two ears that resulted when IDLs were presented. [Work supported by NIDCD and AFOSR.]

Story Recall under Monaural and Binaural Conditions

Recall of a short story is ordinarily the same whether it is heard in the left, right, or both ears. It has been reported that many patients with severe cerebral dysfunctions (including brain damage, major psychiatric disorders, and learning disabilities in children) perform much better with one ear than the other (monaural asymmetry) and that binaural performance is worse than with the better ear alone (binaural interference). Blocking the poorer ear with an earplug is said to significantly improve speech comprehension in daily life. Because of the theoretical and practical significance of these reports, we have attempted a replication. We studied patients with anterior temporal lobectomy because it was proposed that the underlying mechanism of monaural asymmetry and binaural interference in all clinical categories may involve temporal lesions or abnormal inhibition of one temporal lobe by the other. We were unable to confirm the previous reports.