Benefits Of Binaural Hearing Research Articles

Interaural time difference sensitivity with high rate electrical pulse trains in bilateral cochlear implant users

Interaural time differences (ITDs) are an important cue for obtaining binaural hearing benefits. Bilateral cochlear implant (BiCI) users have shown poor ITD sensitivity when using clinical processors, but have some ITD sensitivity with carefully controlled stimuli presented using synchronized research processors. In BiCI users, low stimulation rates yield best ITD sensitivity, but declines as the stimulation rate increases. However, high rates are typically needed for good speech understanding, which poses a conundrum for maximizing the benefit of BiCIs. Aperiodic high-rate stimulation has been shown to promote ITD sensitivity. However, it is uncertain whether this improvement is due to changes in the loudness level, which may provide an envelope ITD cue. In this study, we tested this hypothesis by measuring ITD just noticeable differences (JNDs) with 4000-Hz electrical pulse trains. Pulse trains either had: (1) constant amplitude and rate; (2) aperiodic timing in the pulses; and (3) aperiodic timing + a random amplitude applied to each pulse. Results have implications in determining whether aperiodic high-rate stimulation can be useful for restoring ITD sensitivity. [Work supported by NIH-NIDCD (R01DC003083 to Ruth Litovsky) and NIH-NICHD (P30HD03352 to the Waisman Center).]

Single-sided Deafness Cochlear Implantation

Although there are various available treatment options for unilateral severe-to-profound hearing loss, these options do not provide the benefits of binaural hearing since sound is directed from the poorer ear to the better ear. The purpose of this investigation was to review our center's experience with cochlear implantation in such patients in providing improved auditory benefits and useful binaural hearing. Retrospective chart review. Twelve adult patients and four pediatric patients with unilateral severe-to-profound hearing loss received an implant in the poorer ear. Outcome measures performed preoperatively on each ear and binaurally included consonant-nucleus-consonant (CNC) monosyllabic words and sentences in noise. The mean pure-tune average in the better ear was within normal range. Test scores revealed a significant improvement in CNC and sentence in noise test scores from the preoperative to most recent postoperative evaluation in the isolated implant ear. All adult subjects use the device full-time. The data reveal significant improvement in speech perception performance in quiet and in noise in patients with single-sided deafness after implantation. Performance might depend on factors including length of hearing loss, age at implantation, and device usage.

Time-Varying Distortions of Binaural Information by Bilateral Hearing Aids: Effects of Nonlinear Frequency Compression.

In patients with bilateral hearing loss, the use of two hearing aids (HAs) offers the potential to restore the benefits of binaural hearing, including sound source localization and segregation. However, existing evidence suggests that bilateral HA users’ access to binaural information, namely interaural time and level differences (ITDs and ILDs), can be compromised by device processing. Our objective was to characterize the nature and magnitude of binaural distortions caused by modern digital behind-the-ear HAs using a variety of stimuli and HA program settings. Of particular interest was a common frequency-lowering algorithm known as nonlinear frequency compression, which has not previously been assessed for its effects on binaural information. A binaural beamforming algorithm was also assessed. Wide dynamic range compression was enabled in all programs. HAs were placed on a binaural manikin, and stimuli were presented from an arc of loudspeakers inside an anechoic chamber. Stimuli were broadband noise bursts, 10-Hz sinusoidally amplitude-modulated noise bursts, or consonant–vowel–consonant speech tokens. Binaural information was analyzed in terms of ITDs, ILDs, and interaural coherence, both for whole stimuli and in a time-varying sense (i.e., within a running temporal window) across four different frequency bands (1, 2, 4, and 6 kHz). Key findings were: (a) Nonlinear frequency compression caused distortions of high-frequency envelope ITDs and significantly reduced interaural coherence. (b) For modulated stimuli, all programs caused time-varying distortion of ILDs. (c) HAs altered the relationship between ITDs and ILDs, introducing large ITD–ILD conflicts in some cases. Potential perceptual consequences of measured distortions are discussed.

Bilateral use of active middle ear implants: speech discrimination results in noise.

Binaural sound reception has advantages over unilateral perception, including better localization and sound quality as well as speech and tone reception in both quiet and noisy environments. Up to now, most active middle ear implant (AMEI) users have been unilaterally implanted, but patient demand for an implant on the other side is increasing. Ten bilaterally-AMEI implanted native German-speaking adults were included in the study. The Oldenburg sentence test was used to measure speech reception thresholds in noise. The subject's signal-to-noise ratio (SNR) at a speech reception score of 50% was calculated for different noise conditions. SRT was measured as a function of noise condition (nc) and listening condition (lc)-for example, SRT (lc, nc), with nc from S0N0, S0N-90, or S0N90 and lc from left, right or both. For each noise condition, the squelch effect and the binaural summation effect were calculated. Patients in this study demonstrated improvement with bilateral AMEIs compared to right or left AMEI only in all three tested listening conditions. Statistical significance was found in the S0N0 condition to favor usage of bilateral AMI versus either the right or left side only. The benefits of binaural hearing are well known, also in normal-hearing individuals. In the future every bilateral implantation should be a part of the clinical routine. Bilateral implantation can help to reduce problems in background noise and restore directional hearing.

Availability of binaural cues for pediatric bilateral cochlear implant recipients.

Bilateral implant recipients theoretically have access to binaural cues. Research in postlingually deafened adults with cochlear implants (CIs) indicates minimal evidence for true binaural hearing. Congenitally deafened children who experience spatial hearing with bilateral CIs, however, might perceive binaural cues in the CI signal differently. There is limited research examining binaural hearing in children with CIs, and the few published studies are limited by the use of unrealistic speech stimuli and background noise. The purposes of this study were to (1) replicate our previous study of binaural hearing in postlingually deafened adults with AzBio sentences in prelingually deafened children with the pediatric version of the AzBio sentences, and (2) replicate previous studies of binaural hearing in children with CIs using more open-set sentences and more realistic background noise (i.e., multitalker babble). The study was a within-participant, repeated-measures design. The study sample consisted of 14 children with bilateral CIs with at least 25 mo of listening experience. Speech recognition was assessed using sentences presented in multitalker babble at a fixed signal-to-noise ratio. Test conditions included speech at 0° with noise presented at 0° (S0N0), on the side of the first CI (90° or 270°) (S0N1stCI), and on the side of the second CI (S0N2ndCI) as well as speech presented at 0° with noise presented semidiffusely from eight speakers at 45° intervals. Estimates of summation, head shadow, squelch, and spatial release from masking were calculated. Results of test conditions commonly reported in the literature (S0N0, S0N1stCI, S0N2ndCI) are consistent with results from previous research in adults and children with bilateral CIs, showing minimal summation and squelch but typical head shadow and spatial release from masking. However, bilateral benefit over the better CI with speech at 0° was much larger with semidiffuse noise. Congenitally deafened children with CIs have similar availability of binaural hearing cues to postlingually deafened adults with CIs within the same experimental design. It is possible that the use of realistic listening environments, such as semidiffuse background noise as in Experiment II, would reveal greater binaural hearing benefit for bilateral CI recipients. Future research is needed to determine whether (1) availability of binaural cues for children correlates with interaural time and level differences, (2) different listening environments are more sensitive to binaural hearing benefits, and (3) differences exist between pediatric bilateral recipients receiving implants in the same or sequential surgeries.

Evaluation of the benefits of binaural hearing on the telephone for children with hearing loss.

There is a paucity of published studies examining how children with hearing loss understand speech over the telephone. Previous studies on adults with hearing aids have suggested that adults with bilateral hearing aids experience significant difficulty recognizing speech on the telephone when listening with one ear, but the provision of telephone input to both ears substantially improved speech understanding. The objectives of this study were to measure speech recognition in quiet and in noise for a group of older children with hearing loss over the telephone and to evaluate the effects of binaural hearing (e.g., DuoPhone) on speech recognition over the telephone. A cross-sectional, repeated-measures design was used in this study. A total of 14 children, ages 6-14 yr, participated in the study. Participants were obtained using convenience sampling from a nonprofit clinic population. Speech recognition in quiet and in noise with binaural versus monaural telephone input was compared in pediatric participants. Monosyllabic word recognition was assessed in quiet and classroom noise set at 50 dBA in conditions with monaural and binaural (DuoPhone) telephone input. The children's speech recognition in quiet and in noise was significantly better with binaural telephone input relative to monaural telephone input. To obtain optimal performance on the telephone, the following considerations may apply: (1) use of amplification with binaural streaming capabilities (e.g., DuoPhone), (2) counseling of family and children on how to best use the telephone, (3) provision of telecoil with microphone attenuation for improved signal-to-noise ratio, and (4) use of probe tube measures to verify the appropriateness of the telephone programs.

Current and Developing Management of Single‐Sided Deafness

Program Description: The single-sided deafness (SSD) handicap has been underestimated. The purpose of this miniseminar is to present the latest research on the benefits of binaural hearing (Sig Soli, PhD), and the impact of SSD on childhood development and school performance (Nancy Young, MD). The different rehabilitation methods available will be presented, including osseointegrated bone conduction technologies (Jack J. Wazen, MD) and nonsurgical options (John Goddard, MD). Future trends and clinical research on the use of cochlear implants in SSD will be presented (Bruce Gantz, MD, and Tom Roland, MD). Open discussion, questions, and audience participation will follow the presentations. Educational Objectives: (1) Recognize the benefits of binaural hearing in children and adults and the potential deficits imposed by SSD. (2) Differentiate between surgical and nonsurgical options in the rehabilitation of SSD. (3) Use developing technologies and clinical research in the rehabilitation of SSD, including the use of cochlear implants.

Unilateral Deafness in Children

Recently, several studies have shown that a cochlear implant is a suitable treatment for hearing rehabilitation of adults with unilateral sensorineural hearing loss (UHL), and benefits for speech comprehension in noise and localization have been demonstrated. The aim of this clinical study was to evaluate the benefit of cochlear implantation in children with UHL in comparison to their unaided listening situation. Prospective repeated measures single subject design. Tertiary referral center; cochlear implant (CI) program Three children (4, 10, and 11 yr) with noncongenital UHL resulting from different causes were enrolled in the study. After extensive consultation with each family and confirming CI-candidacy, each child received a cochlear implant. Open set speech recognition measures in competing background noise and tests of sound localization were performed for unaided preoperative and CI-aided postimplant intervals after 6 and 12 months. The parent and child versions of the Speech, Spatial and Qualities scale (SSQ) were used for subjective evaluation of hearing at preimplant and 12-month postimplant intervals. All children consistently use their CI 1 year postimplant. Our preliminary results suggest binaural hearing benefits for speech understanding in noise, localization ability and subjectively perceived hearing ability for school-aged children with UHL. Trends for CI-benefits in younger preschoolaged children are confirmed through subjective assessment reported by the parents. The benefits in hearing performance suggest binaural integration and processing of electric and acoustic stimulation arriving at 2 different ears is possible for children with UHL.

Sound Localization in Noise by Normal-Hearing Listeners and Cochlear Implant Users

This study aimed to characterize horizontal plane sound localization in interfering noise at different signal-to-noise ratios (SNRs) and to compare performance across normal-hearing listeners and users of unilateral and bilateral cochlear implants (CIs). CI users report difficulties with listening in noisy environments. Although their difficulties with speech understanding have been investigated in several studies, the ability to localize sounds in background noise has not extensively been examined, despite the benefits of binaural hearing being greatest in noisy situations. Sound localization is a measure of binaural processing and is thus well suited to assessing the benefit of bilateral implantation. The results will inform clinicians and implant manufacturers how to focus their efforts to improve localization with CIs in noisy situations. Six normal-hearing listeners, four unilateral, and 10 bilateral CI users indicated the perceived location of sound sources using a light pointer method. Target sounds were noise pulses played from one of 11 loudspeakers placed between -80 and +80 degrees in the frontal horizontal plane in the free field. Localization was assessed in quiet and in diffuse background noise at SNRs between +10 and -7 dB. Speech reception thresholds were measured and their relation to the localization results examined. Localization performance declined with decreasing SNR: target sounds were perceived closer to the median plane and the standard deviation of responses increased. Localization performance across groups was compared using a measure of "Spatial Resolvability" (SR). This measure gives the angular separation between two sound sources that would enable an ideal observer to correctly distinguish them 69.1% of the time. For all participants SR increased with decreasing SNR, that is, at low SNRs the spatial separation between sound sources remained distinguishable only when it was larger. Normal-hearing participants performed best, with SR between 1.4 and 5.1 degrees in quiet. Bilateral CI users showed SR between 8.3 and 43.6 degrees in quiet, corresponding approximately to the spatial resolution of normal-hearing listeners at an SNR of -5 dB. Most bilateral CI users had lost the ability to correctly determine which side the sound came from at an SNR of -3 dB. Overall, the SNR had to be at least +7 dB to achieve localization performance near to that in quiet for all bilateral CI users. No significant correlation was found between spatial resolution and speech reception thresholds, but the speech processor sensitivity setting did significantly affect performance. Unilateral CI users showed the most severe localization problems, with only two of four participants being able to correctly determine which side sounds came from in quiet. This study is the first to examine sound localization with CIs at various SNRs and to compare it with normal hearing. The results confirm that localization with CIs is strongly disrupted in noisy situations. Bilateral CIs were shown to be clearly superior over unilateral CIs for localization in quiet and in noisy situations. With bilateral CIs, localization declined at moderately high absolute noise levels (>63 dB SPL), suggesting that an extension of the acoustic-dynamic range to higher levels would be beneficial. The absence of a relation between speech reception thresholds and spatial resolution highlights the need for additional clinical tests to assess the binaural benefit of a second implant.

Cochleaimplantatversorgung

In recent years the indication criteria for cochlear implantation (CI) have changed. To gain optimal benefits, early implantation in prelingually deaf children is necessary. Even additional disabilities are no longer contraindications for CI. Nowadays the criteria for implantation not only include deafness but also residual hearing. Combined electric-acoustic stimulation has been established as a treatment option in patients with hearing still functioning in the low frequencies. Due to the benefits of binaural hearing, bilateral CI has become standard over the last decade. Recent experience has shown the benefits of CI in unilateral deafness and in cases of severe tinnitus. The actual benefit of CI shows great inter-individual differences. We usually expect (re-)habilitation of language communication skills with implantation.

The multi-channel cochlear implant: Past, present and future perspectives

Initial research demonstrated that only low frequencies could be mimicked with rate of electrical stimulation, and thus multi-channel rather than single-channel stimulation was required for the place coding of the mid-high speech frequencies.Place coding of mid-high frequencies was best achieved with electrodes inside the cochlea. Furthermore, correct biomechanical properties of a multiple electrode bundle were required for it to pass around the cochlear spiral to the speech frequency region.Biological studies showed too that intra-cochlear electrodes could be used with minimal trauma, safe electrical stimulus parameters, and methods to prevent inner ear infection and meningitis.The crucial discoveries for coding speech with electrical stimulation have been based on the discovery of: 1) the fact the brain processes frequency information along spatial and temporal channels, and 2) that the first patient experienced vowels when stimulating different electrodes that corresponded to the place of excitation for single formant vowels in people with normal hearing. The inaugural and subsequent speech processing strategies extracted frequencies of special importance for speech intelligibility, and transmitted the information along place coding channels. The voicing frequency and/or amplitude, was coded as temporal information across these spatial channels. As a result a great majority of severely-to-profoundly deaf people with previous hearing can not only communicate when electrical stimulation is combined with lipreading, but with electrical stimulation alone. In addition, the benefits of binaural hearing with bilateral cochlear implants or an implant in one ear and hearing aid in the other ear have been realized.Related psychophysical research has discovered the basic perceptual skills that process the complex patterns of brain excitation that underlie speech recognition both in the one ear as well as bilateral implants.In addition the development of the perceptual skills in the maturing child for speech recognition, have been discovered.In the future high fidelity sound should be achieved by providing the fine temporo-spatial patterns of excitation and preserving the peripheral nerve network. This could require the release of nerve growth factors and the development of electrodes using nanotechnology. Copyright © 2009 John Wiley & Sons, Ltd.

Personal reflections on the multichannel cochlear implant and a view of the future

The multichannel cochlear implant is the first neural prosthesis to effectively and safely bring electronic technology into a direct physiological relation with the central nervous system and human consciousness. It is also the first cochlear implant to give speech understanding to tens of thousands of persons with profound deafness and spoken language to children born deaf in more than 80 countries. In so doing, it is the first major advance in research and technology to help deaf children communicate since Sign Language of the Deaf was developed at the Paris deaf school (L'Institut National de Jeunes Sourds de Paris) >200 years ago. Furthermore, biomedical research has been fundamental for ensuring that the multielectrode implant is safe as well as effective. More recent research has also shown that bilateral implants confer the benefits of binaural hearing. Future research using nanotechnology should see high-fidelity sound received, which would help deaf persons communicate in noise and enjoy music. Research should also lead to implants in ears with useful hearing.

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting

Benefits of bilateral cochlear implantation: a review

Although unilateral cochlear implantation generally provides good speech understanding under quiet conditions, cochlear implantation patients frequently report difficulty understanding speech when exposed to background noise and with sound localization. Since these two listening functions require binaural stimulation for normal individuals and hearing aid recipients, it is not surprising that there is growing interest in binaural implants. This update reviews the basics of binaural listening and the advantages and disadvantages of binaural cochlear implantation. Although the psychoacoustic literature has long demonstrated the benefits of binaural hearing, only recently have studies shown improvement in speech intelligibility with bilateral implants compared with unilateral implants. Of the three known binaural mechanisms, the head shadow effect provides greater benefit than binaural squelch or summation. In addition, binaural cochlear implants improve the ability to localize sound. Bilateral implantation provides multiple benefits to patients with severe to profound hearing loss. Research is currently directed at improving speech intelligibility by utilizing evolving technologies in speech-processing strategies.

Sensitivity to Interaural Time Differences in the Inferior Colliculus with Bilateral Cochlear Implants

Bilateral cochlear implantation attempts to increase performance over a monaural prosthesis by harnessing the binaural processing of the auditory system. Although many bilaterally implanted human subjects discriminate interaural time differences (ITDs), a major cue for sound localization and signal detection in noise, their performance is typically poorer than that of normal-hearing listeners. We developed an animal model of bilateral cochlear implantation to study neural ITD sensitivity for trains of electric current pulses delivered via bilaterally implanted intracochlear electrodes. We found that a majority of single units in the inferior colliculus of acutely deafened, anesthetized cats are sensitive to ITD and that electric ITD tuning is as sharp as found for acoustic stimulation with broadband noise in normal-hearing animals. However, the sharpness and shape of ITD tuning often depended strongly on stimulus intensity; some neurons had dynamic ranges of ITD sensitivity as low as 1 dB. We also found that neural ITD sensitivity was best at pulse rates below 100 Hz and decreased with increasing pulse rate. This rate limitation parallels behavioral ITD discrimination in bilaterally implanted individuals. The sharp neural ITD sensitivity found with electric stimulation at the appropriate intensity is encouraging for the prospect of restoring the functional benefits of binaural hearing in bilaterally implanted human subjects and suggests that neural plasticity resulting from previous deafness and deprivation of binaural experience may play a role in the poor ITD discrimination with current bilateral implants.

Characteristics of listening environments: Benefits of binaural hearing and implications for bilateral management

Acoustically, a room's boundaries can be thought of as dirty mirrors. By repeated reflections, these mirrors generate multiple sound images whose intensities decrease with increasing distance. The sound energy received from these images (conditioned by the inverse square law and atmospheric absorption) sums with direct sound from the source, but with delays that are directly proportional to distance. For a time-varying signal such as speech, it is important to distinguish between ‘early’ and ‘late’ reflections. Early reflections enhance perception and arrive from fairly well defined directions. Late reflections generate both energetic and informational masking and arrive from all directions. In effect, late reflections create a diffuse, self-generated noise that adds to the noise from other sources. For all sources, there are inter-aural differences in time of arrival, sound pressure level, and spectrum, together with intra- and inter-aural effects of head movement. These differences and effects are a rich resource of information about source direction and distance, and they facilitate source segregation, selective attention, and release from both energetic and informational masking. To the extent that this information can be preserved in hearing devices, and accessed and used by hearing-impaired listeners, the potential benefits should follow. But deficits of temporal resolution, spectral resolution, bandwidth, and processing skills, together with delays and other effects of signal processing, may limit the benefits – hence the need for prescriptive and performance measures of binaural function.

Behavioral thresholds to binaural cues

Objectives: There is recent interest in bilateral cochlear implantation to obtain the benefits of binaural hearing. This interest necessitates development of animal models to examine the effects of bilateral implants on the binaural system. Our goal is to develop the unanesthetized rabbit as a model to study behavior and physiology with bilateral implants. This species was chosen because of the wealth of the physiological data from normal animals. However, there is no comparable behavioral data in rabbits. Thus, for this study we behaviorally tested the ability of rabbits to discriminate interaural time differences (ITDs). Methods: Normal hearing Dutch-belted rabbits were trained to discriminate ITDs using conditioned avoidance. A tracking method was used to determine the threshold interaural time difference (ITD) that was discriminable between a reference ITD and a warning ITD. Results: The minimum perceptual threshold was 78 μs at a reference ITD of 100 μs. At 0 μs reference ITD the threshold was 109 μs, increasing to 245 μs at reference ITD of 300 μs. Conclusion: Compared to human beings, the most sensitive region for ITD detection in rabbits is lateralized (100 μs instead of 0 μs) and thresholds are higher (78 μs instead of ∼15 μs). Surprisingly, the rabbit behavioral thresholds are worse than those calculated from physiological responses in neurons, which are comparable to human behavioral thresholds. This study advances the goal of using rabbits as a model system for bilateral cochlear implants.

The benefit of binaural hearing in a cocktail party: effect of location and type of interferer.

The "cocktail party problem" was studied using virtual stimuli whose spatial locations were generated using anechoic head-related impulse responses from the AUDIS database [Blauert et al., J. Acoust. Soc. Am. 103, 3082 (1998)]. Speech reception thresholds (SRTs) were measured for Harvard IEEE sentences presented from the front in the presence of one, two, or three interfering sources. Four types of interferer were used: (1) other sentences spoken by the same talker, (2) time-reversed sentences of the same talker, (3) speech-spectrum shaped noise, and (4) speech-spectrum shaped noise, modulated by the temporal envelope of the sentences. Each interferer was matched to the spectrum of the target talker. Interferers were placed in several spatial configurations, either coincident with or separated from the target. Binaural advantage was derived by subtracting SRTs from listening with the "better monaural ear" from those for binaural listening. For a single interferer, there was a binaural advantage of 2-4 dB for all interferer types. For two or three interferers, the advantage was 2-4 dB for noise and speech-modulated noise, and 6-7 dB for speech and time-reversed speech. These data suggest that the benefit of binaural hearing for speech intelligibility is especially pronounced when there are multiple voiced interferers at different locations from the target, regardless of spatial configuration; measurements with fewer or with other types of interferers can underestimate this benefit.

Results of the bone-anchored hearing aid in unilateral hearing loss.

The advantages of binaural hearing are well established and universally accepted. However, a tendency remains to withhold the benefits of binaural hearing to adults and children with one normal ear. The purpose of this study is to demonstrate the benefit of the bone-anchored hearing aid (BAHA) in a group of patients with unilateral conductive or mixed hearing loss. This is a prospective study of nine patients (five males and four female patients) with conductive or mixed hearing loss who met the criteria for BAHA except for having normal hearing in the other ear. They had congenital aural atresia or mastoidectomies secondary to chronic ear infections with or without cholesteatoma or had a temporal bone tumor excised Patients had evaluations before and after implantation, including audiological testing and responses to a standardized hearing handicap questionnaire. Statistical analyses of the data were made using the Wilcoxon signed rank test and the paired Student t test for repeated measures. All patients had tonal and spondee threshold improvement with BAHA when compared with thresholds before treatment. Speech recognition performance in BAHA-aided conditions was comparable to the patient's best score in unaided condition. Patients reported a significant improvement in their hearing handicap scores with the BAHA. The use of BAHA has significantly improved the hearing handicap scores in patients with unilateral conductive or mixed hearing loss. The proven safety and efficacy of the device promote its use in unilateral cases that traditionally had been left unaided.

Benefit of binaural hearing in a multi-source environment. II. Speech intelligibility.

A multi-source listening environment was simulated under headphones by recording signals through KEMAR in a sound-deadened room. Seven loudspeakers were each positioned in the frontal plane 5 ft from KEMAR at 30-deg increments, ranging from +90 (right) to −90 (left). The recorded signals (IEEE Harvard sentences) were digitally mixed and played back under headphones in a sound-proof booth using a Digital Audio Tape (DAT) player. Speech intelligibility was measured for a ‘‘target’’ sentence in the presence of various ‘‘jammers.’’ Three variables were manipulated. First, the number of ‘‘jammers’’ was either none, one, two, or three. Second, the relative location of the targets and jammers was varied, such that they were either in close proximity, widely separated, or some of each. Third, the jammer content comprised of either other sentences, speech-shaped noise, babble or time-reversed sentences. Normal-hearing listeners were tested under binaural and monaural conditions. On each trial the location of the target sentence was known, and the percentage of key words correctly identified is reported. Speech intelligibility was degraded as the number of jammers and as the target proximity to the jammers was increased. [Work supported by NIH DC02696, DC00100-21.]