Binaural Gain Research Articles

Dependence of binaural gain for infrasound on interaural phase difference.

Increasing complaints about infrasound have generated interest in understanding its perception, including binaural effects. This study investigated the level difference between monaural and binaural presentation required for detection and equal loudness (binaural gain) for pure tones with frequencies of 8, 32, and 400 Hz and an 8 Hz sinusoidally amplitude-modulated tone with diotic 400 Hz carrier. Monaural stimuli were compared to binaural stimuli with interaural phase differences (IPDs) of 0°, 90°, and 180° in two experiments: absolute threshold measurements and loudness matching at 40 phons. The latter was repeated with transposed tones (400 Hz carrier multiplied by a half-wave-rectified 8 Hz sinusoid). When expressed as differences in sound pressure level, similar binaural gain was found across all stimulus types under the diotic condition. Confirming previous studies, the gain was larger at supra-threshold levels (40 phons) than at threshold. However, when the loudness-matching results were expressed as binaural gain with respect to the loudness level, they became 17.5, 11.2, and 5.8 phons for the 8, 32, and 400 Hz stimuli, respectively. Results for the 8 Hz pure tone and the transposed stimulus were IPD dependent.

Simple reaction time for broadband sounds compared to pure tones

Although many studies have explored the relation between reaction time (RT) and loudness, including effects of intensity, frequency, and binaural summation, comparable work on spectral summation is rare. However, most real-world sounds are not pure tones and typically have bandwidths covering several critical bands. Since comparing to a 1-kHz pure tone, the reference tone, is important for loudness measurement and standardization, the present work focuses on comparing RTs for broadband noise to those for 1-kHz pure tones in three experiments using different spectral and binaural configurations. The results of Experiments 1 and 2 yield good quantitative agreement with spectral loudness summation models for moderate and high sound pressure levels, measured using both pink noise covering almost the entire hearing range and bandpass-filtered pink noise with different center frequencies. However, at lower levels, the RT measurements yield an interaction of level and bandwidth, which is not in line with loudness scaling data. In Experiment 3, which investigated the binaural summation of broadband sounds, the binaural gain for white noise was determined to be 9 dB, which is somewhat larger than what had been found in previous RT measurements using 1-kHz pure tones.

Binaural loudness gain measured by simple reaction time.

In order to yield equal loudness, different studies using scaling or matching methods have found binaural level differences between monaural and diotic presentations ranging from less than 2 dB to as much as 10 dB. In the present study, a reaction time methodology was employed to measure the binaural level difference producing equal reaction time (BLDERT). Participants had to respond to the onset of 1-kHz pure tones with sound pressure levels ranging from 45 to 85 dB, and being presented to the right, the left, or both ears. Equal RTs for monaural and diotic presentation (BLDERTs) were obtained with a level difference of approximately 5 dB. A second experiment showed that different results obtained for the left and right ear are largely due to the responding hand, with ipsilateral responses being faster than contralateral ones. A third experiment investigated the BLDERT for dichotic stimuli, tracing the transition between binaural and monaural stimulation. The results of all three RT experiments are consistent with current models of binaural loudness and contradict earlier claims of perfect binaural summation.

Understanding speech in noise after correction of congenital unilateral aural atresia: Effects of age in the emergence of binaural squelch but not in use of head-shadow

Objective Unilateral hearing loss causes difficulty hearing in noise (the “cocktail party effect”) due to absence of redundancy, head-shadow, and binaural squelch. This study explores the emergence of the head-shadow and binaural squelch effects in children with unilateral congenital aural atresia undergoing surgery to correct their hearing deficit. Adding patients and data from a similar study previously published, we also evaluate covariates such as the age of the patient, surgical outcome, and complexity of the task that might predict the extent of binaural benefit – patients’ ability to “use” their new ear – when understanding speech in noise. Methods Patients with unilateral congenital aural atresia were tested for their ability to understand speech in noise before and again 1 month after surgery to repair their atresia. In a sound-attenuating booth participants faced a speaker that produced speech signals with noise 90 degrees to the side of the normal (non-atretic) ear and again to the side of the atretic ear. The Hearing in Noise Test (HINT for adults or HINT-C for children) was used to estimate the patients’ speech reception thresholds. The speech-in-noise test (SPIN) or the Pediatric Speech Intelligibility (PSI) Test was used in the previous study. Results There was consistent improvement, averaging 5 dB regardless of age, in the ability to take advantage of head-shadow in understanding speech with noise to the side of the non-atretic (normal) ear. There was, in contrast, a strong negative linear effect of age ( r 2 = .78, selecting patients over 8 years) in the emergence of binaural squelch to understand speech with noise to the side of the atretic ear. In patients over 8 years, this trend replicated over different studies and different tests. Children less than 8 years, however, showed less improvement in the HINT-C than in the PSI after surgery with noise toward their atretic ear (effect size = 3). No binaural result was correlated with degree of hearing improvement after surgery. Conclusions All patients are able to take advantage of a favorable signal-to-noise ratio in their newly opened ear; that is with noise toward the side of the normal ear (but this physical, bilateral, head-shadow effect need not involve true central binaural processing). With noise toward the atretic ear, the emergence of binaural squelch replicates between two studies for all but the youngest patients. Approximately 2 dB of binaural gain is lost for each decade that surgery is delayed, and zero (or poorer) binaural benefit is predicted after 38 years of age. Older adults do more poorly, possibly secondary to their long period of auditory deprivation. At the youngest ages, however, binaural results are different in open- and closed-set speech tests; the more complex hearing tasks may involve a greater cognitive load. Other cognitive abilities (late evoked potentials, grey matter in auditory cortex, and multitasking) show similar effects of age, peaking at the same late-teen/young-adult period. Longer follow-up is likely critical for the understanding of these data. Getting a new ear may be – like multitasking – challenging for the youngest and oldest subjects.

A two-stage binaural speech enhancement approach for hearing aids with preserving binaural benefits in noisy environments

Speech enhancement is one of the most crucial functions, if not the most, in hearing aids, as hearing impaired people have great difficulty in understanding speech in noisy environments. In this paper, we propose a two-stage binaural speech enhancement approach for hearing aids, which consists of interference estimation by pre-trained adaptive filters and speech enhancement using the Wiener filters. Main attention is then paid to the theoretical analysis of this system and the experimental comparisons with the traditional binaural speech enhancement approaches. The comparisons are conducted with the following two considerations: interference suppression performance and the ability in preserving binaural cues which give birth to listener's own “binaural gain.” We finally give the general discussion on this proposed binaural speech enhancement algorithm from the viewpoints of theory, through implementation, to evaluation.

Directional loudness in an anechoic sound field, head-related transfer functions, and binaural summation

The effect of sound incidence angle on loudness was investigated using real sound sources positioned in an anechoic chamber. Eight normal-hearing listeners produced loudness matches between a frontal reference location and seven sources placed at other directions, both in the horizontal and median planes. Matches were obtained via a two-interval, adaptive forced-choice (2AFC) procedure for three center frequencies (0.4, 1, and 5 kHz) and two overall levels (45 and 65 dB SPL). The results showed that loudness is not constant over sound incidence angles, with directional sensitivity varying over a range of up to 10 dB, exhibiting considerable frequency dependence, but only minor effects of overall level. The pattern of results varied substantially between subjects, but was largely accounted for by variations in individual head-related transfer functions. Modeling of binaural loudness based on the at-ear signals favored a sound-power summation model, according to which the maximum binaural gain is only 3 dB, over competing models based on larger gains, or on the summation of monaural loudness indices.

Auditory feature detection for stimuli presented from different directions

The processing of stimulus features by the visual system is commonly studied by measuring response times (RTs) for detection of targets presented with a varying number of distracters. In audition, however, interpretation of the interaction between target and distracters is complicated by effects like masking, binaural gain and fusion. In the present paradigm, which uses stimuli presented from different directions in the horizontal plane, these confounding effects were either minimized or kept constant. Targets were synthetic vowels and RTs were measured for detection of three features: F0, spectrum (type of vowel) and direction. Both single features and conjunctions were studied. Independent variables were the type of distracters (synthetic vowels or spectrally shaped noise) and their number. Results show that the effect of the number of distracters on the RT is smallest for the spectrum feature; RTs for the detection of F0 are largest and vary considerably across subjects. For conjunctions of features, the RTs lie, as expected, between the RTs for the single features. The effect of the type of distracter on the RT is small—this indicates that the processing involved in segregating vowels from noise is not more efficient than that used for segregating vowels from other vowels.

The cocktail party effect: Research and applications

The ‘‘cocktail party problem,’’ defined in 1953 by Cherry [J. Acoust. Soc. Am. 25, 975–979 (1953)] as ‘‘how do we recognize what one person is saying when others are speaking at the same time’’ has been the subject of a considerable number of studies in the last 45 years. Whereas Cherry already hypothesized that there are multiple effects that contribute to the ability to extract one speaker out of a babble, the term ‘‘cocktail party effect’’ has been claimed by only one of them: the influence of spatial separation of the voices. One important conclusion from past research on the cocktail party effect is that the truly binaural gain (the ‘‘unmasking’’) is, in general, relatively small (2–4 dB). The additional ‘‘acoustic’’ gain due to head shadow effects may be larger but depends strongly on the circumstances. In the present paper the research will be reviewed including recent evidence that much larger binaural gains may occur when the masker is ‘‘informational’’ in nature [Kidd et al., J. Acoust. Soc. Am. 104, 422–431 (1998)]. In addition, several applications based on the cocktail party effect, such as the use of a virtual auditory display for multiple-speaker communication, will be highlighted.

Binaural speech intelligibility in noise for hearing-impaired listeners.

The effect of head-induced interaural time delay (ITD) and interaural level differences (ILD) on binaural speech intelligibility in noise was studied for listeners with symmetrical and asymmetrical sensorineural hearing losses. The material, recorded with a KEMAR manikin in an anechoic room, consisted of speech, presented from the front (0 degree), and noise, presented at azimuths of 0 degree, 30 degrees, and 90 degrees. Derived noise signals, containing either only ITD or only ILD, were generated using a computer. For both groups of subjects, speech-reception thresholds (SRT) for sentences in noise were determined as a function of: (1) noise azimuth, (2) binaural cue, and (3) an interaural difference in overall presentation level, simulating the effect of a monaural hearing acid. Comparison of the mean results with corresponding data obtained previously from normal-hearing listeners shows that the hearing impaired have a 2.5 dB higher SRT in noise when both speech and noise are presented from the front, and 2.6-5.1 dB less binaural gain when the noise azimuth is changed from 0 degree to 90 degrees. The gain due to ILD varies among the hearing-impaired listeners between 0 dB and normal values of 7 dB or more. It depends on the high-frequency hearing loss at the side presented with the most favorable signal-to-noise (S/N) ratio. The gain due to ITD is nearly normal for the symmetrically impaired (4.2 dB, compared with 4.7 dB for the normal hearing), but only 2.5 dB in the case of asymmetrical impairment. When ITD is introduced in noise already containing ILD, the resulting gain is 2-2.5 dB for all groups. The only marked effect of the interaural difference in overall presentation level is a reduction of the gain due to ILD when the level at the ear with the better S/N ratio is decreased. This implies that an optimal monaural hearing aid (with a moderate gain) will hardly interfere with unmasking through ITD, while it may increase the gain due to ILD by preventing or diminishing threshold effects.

Auditory processing disorders and problems with Hearing-Aid fitting in old age

The hearing handicap experienced by elderly subjects depends only partially on end-organ impairment. Not only the neural unit loss along the central auditory path-ways contributes to decreased speech discrimination, but also learning processes are slowed down. Diotic listening in elderly people seems to fasten learning of discrimination in critical conditions, as in the case of sensitized speech. This fact, and the binaural gain through the binaural release from masking, stress the superiority, on theoretical grounds, of binaural over monaural hearing-aid fitting.

Auditory processing disorders and problems with Hearing-Aid fitting in old age

The hearing handicap experienced by elderly subjects depends only partially on end-organ impairment. Not only the neural unit loss along the central auditory pathways contributes to decreased speech discrimination, but also learning processes are slowed down. Diotic listening in elderly people seems to fasten learning of discrimination in critical conditions, as in the case of sensitized speech. This fact, and the binaural gain through the binaural release from masking, stress the superiority, on theoretical grounds, of binaural over monaural hearing-aid fitting.

Reception of consonants in a classroom as affected by monaural and binaural listening, noise, reverberation, and hearing aids.

Reception of consonants was studied with normal-hearing subjects in a sound-treated classroom, at reverberation times T ≃0.3 and 0.6 sec, to compare binaural and monaural reception, with and without hearing aids, in the presence of an impulsive noise (16 imp/sec) and a quasisteady noise (a babble of eight voices). The consonants were spoken in words inbedded in a rapidly spoken carrier phrase. The speech and noise sources subtended an angle of 60° on a circle 11 ft in radius centered on the listener, to give a large advantage for binaural reception. Binaural gain was taken as the difference in speech-to-noise ratios for 60% correct reception comparing binaural and monaural results. The binaural gain at short reverberation, with unaided listening, was 5 dB in the presence of the babble and 4 dB in the presence of the impulsive noise. The introduction of hearing aids and the increase in reverberation each caused the binaural gain to decrease to 3 dB. The small increase in reverberation caused a substantial decrease in reception under the noise conditions tested. Analysis of the consonant responses to reflect reception of the phonetic features of voicing, manner, and place, for both initial and final consonants, indicated that the acoustic conditions of reverberation and binaural listening affected feature reception in predictable ways.

Monaural and Binaural Free-Field Speech Reception through Ear-Level Hearing Aids under Noise and Reverberation

Speech reception was studied in a room at reverberation times T = 0.3 and 0.6 sec, to compare binaural and monaural reception through ear-level hearing aids in the presence of a babble of eight voices. Some subjects (Ss) had normal hearing and some had severe sensorineural hearing impairment with bilaterally symmetrical audiograms. The speech and noise sources subtended an arc of 60° on a circle 11 ft in radius centered on the S's head. Binaural gain, the difference in speech to noise ratios for 50% correct speech reception comparing binuaral and monaural results, was 3 dB for normal Ss at both reverberant conditions. The binaural gain for impaired Ss varied from 3 dB to 0; those with previous binaural experience tended to show greater binaural gain. The prolongation of reverberation caused a reduction in reception. In presence of the masking noise, the reduction was about 15% correct response for both normal and impaired Ss. In quiet, normal Ss' reception was not influenced by the prolonged reverberation but the impaired Ss showed about 10% reduction in reception. [Supported by Gallaudet College].

Monaural and Binaural Free-Field Speech Reception under Noise and Reverberation

Speech reception was studied in a single sound-treated room at reverberation times T=0.3 and T=0.6 sec, to compare binaural and monaural reception in the presence of an impulsive noise (16 imp/sec) and a quasisteady noise (a babble of eight voices). The speech and noise sources were fixed at locations, relative to the listener, to give the largest advantage for binaural reception. Binaural gain is taken as the difference in speechto-noise ratios for 60% correct speech reception comparing binaural and monaural results. At T=0.6 sec, binaural gain was 3 dB for both types of noise. At T=0.3 sec the gain was 5 dB for the babble and 4 dB for the impulsive noise. The longer reverberation caused a reduction in reception in both binaural and monaural conditions. These effects were larger for the impulsive noise and for low S/N ratios. The largest reverberation effect reduced reception from 77% to 53% words correct. [Supported by Gallaudet College.]

Predicting binaural gain in intelligibility and release from masking for speech.

A simple, approximate procedure for predicting binaural gain in intelligibility and release from masking for detection of speech in broadband Gaussian noise is presented. The procedure assumes that the effect of binaural processing in the auditory system can be adequately represented by a frequency-dependent reduction in the level of the masking noise. The magnitude of this reduction is derived from data on release from masking for tones. Predictions of intelligibility are based on the Articulation Index as computed for the equivalent masking noise. It is predicted that the binaural gain in intelligibility for speech in white noise is greatest at low intelligibility levels, decreasing to about 3 dB at high intelligibility levels. The relative importance of low- and high-frequency interaural phase opposition in producing a binaural gain in intelligibility depends on the signal-to-noise (S/N) ratio. Low-frequency interaural phase opposition is of greater importance at low S/N ratios. Release from masking for detection represents a limiting case, the binaural gain being roughly 13 dB and dependent primarily on interaural phase information below about 500 Hz. Predictions based on this procedure are fairly consistent with data obtained in an earlier experiment. More data are required, however, for an adequate assessment of the technique. The implications for practical binaural systems are discussed.

Binaural release from masking for speech and gain in intelligibility.

Relative importance of different frequency regions in binaural release from masking (for detection) and binaural gain in intelligibility was investigated. Experiments showed that the release from masking (SπN0 case) for single words in high-level, broad-band Gaussian noise is roughly 13 dB and is determined primarily by interaural phase opposition in the low-frequency (<500 Hz) region. The binaural gain in intelligibility at the 50% level was on the order of 6 dB and only partly dependent on interaural phase opposition in the low-frequency region. Interaural amplitude differences were not considered in the investigation. Subjecting the speech to a large interaural time dealy with the noise binaurally in phase resulted in a relatively constant masking level difference approaching 13 dB over the measured range from 0.5 to 10 msec. The corresponding binaural gain in intelligibility at the 50% level was on the order of 3 dB.

MONAURAL AND BINAURAL SPEECH INTELLIGIBILITY AND THE STEREOPHONIC EFFECT BASED UPON TEMPORAL CUES.

Abstract : A stereo tape was prepared using three talkers separated in 30 degree azimuth steps. Nine ways of connecting the two channels to the two ears were devised, and administered to normal ears and to monaurally defective individuals. Four principles of binaural interaction were enunciated: The Principle of Binaural Gain, the Principle of Redundancy, the Principle of Blurring, and the Principle of Degradation. These principles consider the advantage of a second neural channel, a second 'look' at the stimulus with the same ear, confounding results from receiving information in one ear from noncongruent points in space, and the disadvantage of mixing signals from a normal ear and one in which signals are garbled as a result of a pathological condition. In any one person, speech intelligibility will be the algebraic resultant of whatever principles are operating at the moment.

Some Aspects of Binaural Signal Selection

Two experiments are reported which measure the increase in intelligibility occasioned by listening binaurally to running speech imbedded in interfering signals. In the first experiment, the frequency range of the speech is restricted to one of three ranges: 200–1600, 880–2200, 1660–6100. The interfering signal is broad-band random noise. Under difficult listening (27% intelligibility for homophasic listening) the lowest range shows a binaural improvement of 33% for a change in interaural polarity, and of 28% for an interaural time disparity of 500 μsec. The middle- and high frequency ranges show less binaural gain, but do afford some advantage to two eared listening under difficult conditions. The second experiment compares the effects of different speech waves masking the wanted speech in binaural listening. For the maskers used, the binaural system helps most when the interfering wave is the speaker's own voice or a multiple mixture of many voices. The measured differences between homophasic and binaural listening are small but statistically reliable. The interaural differences employed (time delay and polarity reversal) are no help when the interfering wave is a female voice, another male voice, or the multiple mixture played backward.