Masker Locations Research Articles

Crossmodal cueing of masker location in a localization-in-noise task

Simpson et al. [JASA 129(4), 2489, (2011)] found that localization of a target presented in a simultaneous masker improved when, on a trial-by-trial basis, a preview of the masking stimulus was presented at the location of the upcoming masker. Subsequent research revealed that this improvement resulted solely from cueing the location of the masker (i.e., cueing spectro-temporal properties of the masker provided no additional benefit). In the present study, we examined the degree to which the benefit of cueing masker location depended on the modality in which this cue was provided. In separate blocks of trials, the location of the masker was cued auditorily, visually (LED activated at the masker location) and audio-visually, and compared to performance in a no-cue baseline. The results revealed a substantial (∼10 dB) benefit of cueing the masker auditorily over the no-cue condition, consistent with previous results. Importantly, there was also a substantial (albeit smaller) benefit of a visual cue (∼6 dB). Performance with a bimodal cue was no different than performance with an auditory cue. Thus, although hearing a sound from the upcoming masker location was most effective, the ability to effectively cue space crossmodally suggests that the spatial information itself is most critical.

Predicting speech-in-speech recognition: Short-term audibility and spatial separation.

Quantifying the factors that predict variability in speech-in-speech recognition represents a fundamental challenge in auditory science. Stimulus factors associated with energetic and informational masking (IM) modulate variability in speech-in-speech recognition, but energetic effects can be difficult to estimate in spectro-temporally dynamic speech maskers. The current experiment characterized the effects of short-term audibility and differences in target and masker location (or perceived location) on the horizontal plane for sentence recognition in two-talker speech. Thirty young adults with normal hearing (NH) participated. Speech reception thresholds and keyword recognition at a fixed signal-to-noise ratio (SNR) were measured in each spatial condition. Short-term audibility for each keyword was quantified using a glimpsing model. Results revealed that speech-in-speech recognition depended on the proportion of audible glimpses available in the target + masker keyword stimulus in each spatial condition, even across stimuli presented at a fixed global SNR. Short-term audibility requirements were greater for colocated than spatially separated speech-in-speech recognition, and keyword recognition improved more rapidly as a function of increases in target audibility with spatial separation. Results indicate that spatial cues enhance glimpsing efficiency in competing speech for young adults with NH and provide a quantitative framework for estimating IM for speech-in-speech recognition in different spatial configurations.

Masked Speech Recognition as a Function of Masker Location for Cochlear Implant Users With Single-Sided Deafness.

Cochlear implant (CI) recipients with normal or near normal hearing (NH) in the contralateral ear, referred to as single-sided deafness (SSD), experience significantly better speech recognition in noise with their CI than without it, although reported outcomes vary. One possible explanation for differences in outcomes across studies could be differences in the spatial configurations used to assess performance. This study compared speech recognition for different spatial configurations of the target and masker, with test materials used clinically. Sixteen CI users with SSD completed tasks of masked speech recognition presented in five spatial configurations. The target speech was presented from the front speaker (0° azimuth). The masker was located either 90° or 45° toward the CI-ear or NH-ear or colocated with the target. Materials were the AzBio sentences in a 10-talker masker and the Bamford-Kowal-Bench Speech-in-Noise test (BKB-SIN; four-talker masker). Spatial release from masking (SRM) was computed as the benefit associated with spatial separation relative to the colocated condition. Performance was significantly better when the masker was separated toward the CI-ear as compared to colocated. No benefit was observed for spatial separations toward the NH-ear. The magnitude of SRM for spatial separations toward the CI-ear was similar for 45° and 90° when tested with the AzBio sentences, but a larger benefit was observed for 90° as compared to 45° for the BKB-SIN. Masked speech recognition in CI users with SSD varies as a function of the spatial configuration of the target and masker. Results supported an expansion of the clinical test battery at the study site to assess binaural hearing abilities for CI candidates and recipients with SSD. The revised test battery presents the target from the front speaker and the masker colocated with the target, 90° toward the CI-ear, or 90° toward the NH-ear.

Novel Approaches to Measure Spatial Release From Masking in Children With Bilateral Cochlear Implants.

To investigate the role of auditory cues for spatial release from masking (SRM) in children with bilateral cochlear implants (BiCIs) and compare their performance with children with normal hearing (NH). To quantify the contribution to speech intelligibility benefits from individual auditory cues: head shadow, binaural redundancy, and interaural differences; as well as from multiple cues: SRM and binaural squelch. To assess SRM using a novel approach of adaptive target-masker angular separation, which provides a more functionally relevant assessment in realistic complex auditory environments. Children fitted with BiCIs (N = 11) and with NH (N = 18) were tested in virtual acoustic space that was simulated using head-related transfer functions measured from individual children with BiCIs behind the ear and from a standard head and torso simulator for all NH children. In experiment I, by comparing speech reception thresholds across 4 test conditions that varied in target-masker spatial separation (colocated versus separated at 180°) and listening conditions (monaural versus binaural/bilateral listening), intelligibility benefits were derived for individual auditory cues for SRM. In experiment II, SRM was quantified using a novel measure to find the minimum angular separation (MAS) between the target and masker to achieve a fixed 20% intelligibility improvement. Target speech was fixed at either +90 or -90° azimuth on the side closer to the better ear (+90° for all NH children) and masker locations were adaptively varied. In experiment I, children with BiCIs as a group had smaller intelligibility benefits from head shadow than NH children. No group difference was observed in benefits from binaural redundancy or interaural difference cues. In both groups of children, individuals who gained a larger benefit from interaural differences relied less on monaural head shadow, and vice versa. In experiment II, all children with BiCIs demonstrated measurable MAS thresholds <180° and on average larger than that from NH children. Eight of 11 children with BiCIs and all NH children had a MAS threshold <90°, requiring interaural differences only to gain the target intelligibility benefit; whereas the other 3 children with BiCIs had a MAS between 120° and 137°, requiring monaural head shadow for SRM. When target and maskers were separated at 180° on opposing hemifields, children with BiCIs demonstrated greater intelligibility benefits from head shadow and interaural differences than previous literature showed with a smaller separation. Children with BiCIs demonstrated individual differences in using auditory cues for SRM. From the MAS thresholds, more than half of the children with BiCIs demonstrated robust access to interaural differences without needing additional monaural head shadow for SRM. Both experiments led to the conclusion that individualized fitting strategies in the bilateral devices may be warranted to maximize spatial hearing for children with BiCIs in complex auditory environments.

Enhancing the perceptual segregation and localization of sound sources with a triple beamformer.

A triple beamformer was developed to exploit the capabilities of the binaural auditory system. The goal was to enhance the perceptual segregation of spatially separated sound sources while preserving source localization. The triple beamformer comprised a variant of a standard single-channel beamformer that routes the primary beam output focused on the target source location to both ears. The triple beam algorithm adds two supplementary beams with the left-focused beam routed only to the left ear and the right-focused beam routed only to the right ear. The rationale for the approach is that the triple beam processing exploits sound source segregation in high informational masking (IM) conditions. Furthermore, the exaggerated interaural level differences produced by the triple beam are well-suited for categories of listeners (e.g., bilateral cochlear implant users) who receive limited benefit from interaural time differences. The performance with the triple beamformer was compared to normal binaural hearing (simulated using a Knowles Electronic Manikin for Auditory Research, G.R.A.S. Sound and Vibration, Holte, DK) and to that obtained from a single-channel beamformer. Source localization in azimuth and masked speech identification for multiple masker locations were measured for all three algorithms. Taking both localization and speech intelligibility into account, the triple beam algorithm was considered to be advantageous under high IM listening conditions.

Pre-trial and post-trial cueing of masker location in a localization-in-noise task

Localization accuracy for a target presented in a simultaneous masker, whose location varies randomly from trial to trial, improves when a preview of the masker location is provided (by playing a sound from that location) prior to the target + masker interval (i.e., a pre-trial cue) [B. Simpson, Ph.D. dissertation (Wright State University, 2011)]. One explanation is that knowing the masker location allows a listener to establish a “spatial attention filter” at the masker location. The present study compares the effect of such a pre-trial cue to the case in which the cue comes after the target + masker interval (post-trial cueing). That is, the cue is presented either 500 ms prior to the onset of a 60-ms, 100-Hz click-train target embedded in a 60-ms broadband masker, or 500 ms subsequent to the offset of the target + masker stimulus. The data indicate that both cue types lead to similar improvements in performance over the no-cue condition, with the greatest improvement from cueing (~6 dB) seen for localization in the left/right dimension. While these data are roughly consistent with previous results, they cannot be explained by a simple spatial filter hypothesis.

Impact of spatial variability and masker fringe on detectability of brief signal

Seemingly, there should be a close relationship between spatial release from masking and sound localization, but this is not always the case. For example, in binaural detection, randomizing the spatial parameters of the target or masker from trial to trial has little impact on threshold. In contrast, Simpson (Ph.D. dissertation, 2011) found that left/right localization judgments for a 60-ms target masked by a simultaneous 60-ms noise were considerably less accurate (equivalent to 10-dB reduction in SNR) when the location of the masker varied randomly from trial to trial than when the masker location was fixed. However, when a forward masker fringe was added, so that the noise was turned on 500 ms before the target, the impact of location variability was very small (about 1 dB, comparable to the detection literature). To determine if the presence of masker fringe could have limited the impact of spatial variability in previous detection experiments, the current study examines the effect of masker fringe and both target and masker spatial variability on detectability in conditions comparable to those of Simpson. The results will be compared to previous findings and models reported in the binaural detection and sound localization literature.

Listeners Experience Linguistic Masking Release in Noise-Vocoded Speech-in-Speech Recognition.

The purpose of this study was to evaluate whether listeners with normal hearing perceiving noise-vocoded speech-in-speech demonstrate better intelligibility of target speech when the background speech was mismatched in language (linguistic release from masking [LRM]) and/or location (spatial release from masking [SRM]) relative to the target. We also assessed whether the spectral resolution of the noise-vocoded stimuli affected the presence of LRM and SRM under these conditions. In Experiment 1, a mixed factorial design was used to simultaneously manipulate the masker language (within-subject, English vs. Dutch), the simulated masker location (within-subject, right, center, left), and the spectral resolution (between-subjects, 6 vs. 12 channels) of noise-vocoded target-masker combinations presented at +25 dB signal-to-noise ratio (SNR). In Experiment 2, the study was repeated using a spectral resolution of 12 channels at +15 dB SNR. In both experiments, listeners' intelligibility of noise-vocoded targets was better when the background masker was Dutch, demonstrating reliable LRM in all conditions. The pattern of results in Experiment 1 was not reliably different across the 6- and 12-channel noise-vocoded speech. Finally, a reliable spatial benefit (SRM) was detected only in the more challenging SNR condition (Experiment 2). The current study is the first to report a clear LRM benefit in noise-vocoded speech-in-speech recognition. Our results indicate that this benefit is available even under spectrally degraded conditions and that it may augment the benefit due to spatial separation of target speech and competing backgrounds.

Application of a short-time version of the Equalization-Cancellation model to speech intelligibility experiments with speech maskers.

A short-time-processing version of the Equalization-Cancellation (EC) model of binaural processing is described and applied to speech intelligibility tasks in the presence of multiple maskers, including multiple speech maskers. This short-time EC model, called the STEC model, extends the model described by Wan et al. [J. Acoust. Soc. Am. 128, 3678-3690 (2010)] to allow the EC model's equalization parameters τ and α to be adjusted as a function of time, resulting in improved masker cancellation when the dominant masker location varies in time. Using the Speech Intelligibility Index, the STEC model is applied to speech intelligibility with maskers that vary in number, type, and spatial arrangements. Most notably, when maskers are located on opposite sides of the target, this STEC model predicts improved thresholds when the maskers are modulated independently with speech-envelope modulators; this includes the most relevant case of independent speech maskers. The STEC model describes the spatial dependence of the speech reception threshold with speech maskers better than the steady-state model. Predictions are also improved for independently speech-modulated noise maskers but are poorer for reversed-speech maskers. In general, short-term processing is useful, but much remains to be done in the complex task of understanding speech in speech maskers.

The effect of masker spatial uncertainty on sound localization

Previous research from our laboratory has shown that uncertainty about the spatial location of a masking sound (randomly selected from 1 of 239 locations) can dramatically reduce localization accuracy for a simultaneous target relative to the case in which the masker location is known exactly. One possibility is that knowing the masker location enables the listener to establish a spatial attention filter at that location to suppress the masker and better localize the target. In this experiment, the level of masker spatial uncertainty was systematically varied across blocks by varying the number of possible masker locations (1, 2, 4, 8, or 239) and informing subjects about these possible locations prior to the start of each block. Localization errors were found to increase systematically in the left/right, front/back, and up/down dimensions as the number of potential masker locations increased; this effect was most prominent in the left/right dimension, where localization errors increased by nearly 30 degrees across conditions. Moreover, for a masker in a given location, errors generally increased across these levels of masker spatial uncertainty, consistent with the notion that there is a cost to distributing attention across multiple locations.

A computational model of spatial tuning in the auditory cortex in response to competing sound sources

Single neurons in the auditory midbrain are sharply tuned to preferred directions, while cortical neurons show broader tuning [King et al., Hearing Research (2007)] Recent experiments on cortical responses in birds revealed the emergence of spatial tuning to multiple competing sounds in the cortex [Maddox et al., PLoS Biol. (2012)]. In this situation, cortical neurons show broad tuning to single-location stimuli, but develop sharper spatial preference in response to a second competing noise source. We have developed a computational model to match these physiological data. The model takes binaural inputs containing sounds from two locations, and outputs cortical spike trains that emphasize one pre-defined location. In the model, sharply tuned midbrain neurons synapse onto their corresponding interneurons, which then innervate cortical neurons generating the final output. In the presence of stimulus from a pre-defined preferred location, corresponding interneurons actively suppress sources from a pre-defined non-preferred location. The model achieves spatial tuning by performing robustly when the target and masker locations match the pre-defined preferred and non-preferred directions. Looking across cortical neurons tuned to different target and masker combinations, the model provides a mechanism by which binaural inputs from a noisy environment can be separated into independent “streams” based on locations.

Masker location uncertainty reveals evidence for suppression of maskers in two-talker contexts

In many natural settings, spatial release from masking aids speech intelligibility, especially when there are competing talkers. This paper describes a series of three experiments that investigate the role of prior knowledge of masker location on phoneme identification and spatial release from masking. In contrast to previous work, these experiments use initial stop-consonant identification as a test of target intelligibility to ensure that listeners had little time to switch the focus of spatial attention during the task. The first experiment shows that target phoneme identification was worse when a masker played from an unexpected location (increasing the consonant identification threshold by 2.6 dB) compared to when an energetically very similar and symmetrically located masker came from an expected location. In the second and third experiments, target phoneme identification was worse (increasing target threshold levels by 2.0 and 2.6 dB, respectively) when the target was played unexpectedly on the side from which the masker was expected compared to when the target came from an unexpected, symmetrical location in the hemifield opposite the expected location of the masker. These results support the idea that listeners modulate spatial attention by both focusing resources on the expected target location and withdrawing attentional resources from expected locations of interfering sources.

Localization in noise and the role of forward masker fringe.

Previous research suggests that the localization of a target sound in a masking noise is more accurate when the masker is preceded by a forward masker fringe. It is unclear what information listeners are exploiting to produce this improvement in performance. Does the fringe simply reduce spatial uncertainty (by cuing the location of the masker) or does it provide a “context” against which the onset of the signal is more easily discerned? In order to address these questions, we examined conditions in which the masker is (a) pulsed on and off with a 60 ms target (no fringe), (b) immediately preceded by a 500‐ms masker fringe; or (c) preceded by a 500‐ms fringe + a 500‐ms gap. Masker spatial uncertainty was also manipulated by presenting the noise from a fixed and known location throughout a block, or from a location that varied across trials. The results suggest that listeners benefit from the presence of a forward masker fringe even when the masker location is known. However, localization performance is best when this fringe occurs immediately prior to the masker (i.e., no gap), suggesting that onset‐related cues also contribute to the improvement in localization. [Work supported by the AFOSR]

Effect of Stimulus and Recording Parameters on Spatial Spread of Excitation and Masking Patterns Obtained With the Electrically Evoked Compound Action Potential in Cochlear Implants

Spread of excitation within the cochlea in response to electrical stimulation can be measured with the electrically evoked compound action potential (ECAP). Different spread of excitation measurement techniques have been reported in the literature. One method uses a fixed stimulus location while varying the recording electrode along the length of the implanted array. This results in a relatively coarse estimate of spatial spread (SS) along the cochlea. Another method uses a forward-masking paradigm to evaluate the relative overlap of stimulated neural populations between electrodes. Both the probe and recording electrodes are fixed in location while a masker stimulus is systematically applied across electrodes. This method, which yields a more precise estimate of spatial excitation patterns, is termed spatial masking (SM). Five experiments were conducted to examine potential effects of stimulus and/or recording parameters on SS and SM patterns. Experiment 1 examined whether SS patterns were systematically broader than SM patterns across electrodes and subjects. Experiments 2 and 3 evaluated the effects of stimulus level on SS and SM patterns, respectively, to determine whether increased stimulus level systematically resulted in broader patterns. Experiment 4 evaluated whether recording electrode location affected SM patterns, and Experiment 5 evaluated whether SM patterns varied significantly across repeated trials within a test session. Data were collected for 27 ears in 26 adult and teenage subjects (N = 6 ears with Advanced Bionics CII, N = 8 ears with Advanced Bionics HiRes 90K, N = 10 ears with Nucleus 24R[CS], N = 3 ears with Nucleus 24RE[CA] Freedom). A standard forward-masking subtraction paradigm was used for all ECAP measures. For SS patterns, the masker and probe were fixed on the same electrode at the same level while the recording electrode varied across the remaining electrodes in the array. For SM patterns, the probe and recording locations were fixed while the masker location varied across all electrodes except the recording electrode. In experiment 1, SS patterns were broader than SM patterns. Subjects with Advanced Bionics devices exhibited relatively broad patterns for both measures, whereas Nucleus subjects typically exhibited narrower SM functions relative to SS functions. In experiments 2 and 3, there was a significant effect of stimulus level on the spread of both SS and SM patterns in roughly one-third of measures in each experiment. In experiment 4, there was a significant effect of recording electrode location on the width/spread of SM patterns for only 11.5% of comparisons. In experiment 5, there were no significant differences in SM amplitudes across repeated trials for 94% of comparisons, which suggests that ECAP measures are highly robust within a test session. Results showed that SS functions were generally broader than SM functions, which suggests that SS measures reflect volume conduction of the ECAP response along the length of the cochlea. Differences in the spread of SM functions across devices are likely due to differences in modiolar proximity between the respective electrode array designs. Stimulus level had a more significant effect on the spread of SM functions than recording electrode location. Finally, ECAP measures were shown to be highly stable across repeated measurements within a test session; however, repeatability was not assessed across sessions or over extended time intervals.

Speech localization in a multitalker mixture

An experiment was performed that measured, for the frontal audio-visual horizon, how accurately listeners could localize a female-voice target amidst four spatially distributed male-voice maskers. To examine whether listeners can make use of a priori knowledge about the configuration of the sources, performance was examined in two conditions: either the masker locations were fixed (in one of five known patterns) or the locations varied from trial to trial. The presence of maskers disrupted speech localization, even after accounting for reduced target detectability. Averaged across all target locations, the rms error in responses decreased by 20% when a priori knowledge about masker locations was available. The effect was even stronger for the target locations that did not coincide with the maskers (error reduction of 36%), while no change in errors was observed for targets coinciding with maskers. The benefits were reduced when the target-to-masker intensity ratio was increased or when the maskers were in a pattern that made it difficult to make use of the a priori information. The results confirm that localization in speech mixtures is modified by the listener's expectations about the spatial arrangement of the sources.

Psychophysical Versus Physiological Spatial Forward Masking and the Relation to Speech Perception in Cochlear Implants

The primary goal of this study was to determine if physiological forward masking patterns in cochlear implants are predictive of psychophysical forward masking (PFM) patterns. It was hypothesized that the normalized amount of physiological masking would be positively correlated with the normalized amount of psychophysical masking for different masker-probe electrode separations. A secondary goal was to examine the relation between the spatial forward masking patterns and speech perception performance. It was hypothesized that subjects with less channel interaction overall (either psychophysically or physiologically) would have better speech perception ability because of better spectral resolution. Data were collected for 18 adult cochlear implant recipients [N = 9 Clarion CII or HiRes 90K, N = 9 Nucleus 24R(CS)]. Physiological spatial forward masking patterns were obtained with the electrically evoked compound action potential (ECAP) through the implant telemetry system. PFM patterns were obtained using a three-interval, two-alternative forced-choice adaptive procedure. Both measures used a fixed probe electrode with varied masker location. For each subject, spatial forward masking patterns were obtained for three probe electrodes with five masker locations per probe. On an individual basis, the correlation between ECAP FM and PFM was strong for 10 subjects (r = 0.68-0.85, p <or= 0.02), moderately strong for two subjects (r = 0.54-0.55, p = 0.06-0.07), and poor for six subjects (r = 0.13-0.45, p > 0.14). Results across subjects and electrodes showed a highly significant correlation between ECAP FM and PFM (r = 0.55, p < 0.0001); the correlation was strongest for basal electrodes. There was no significant correlation between speech perception and ECAP FM or PFM. Subjects whose ECAP FM patterns correlated well with PFM patterns generally had the poorest speech perception and subjects with the poorest correlations had the best speech perception. ECAP FM and PFM patterns correlated well for two-thirds of the subjects. Although the group correlation was statistically significant, ECAP FM patterns only accounted for 30% of the variance in the PFM measures. This suggests that the ECAP measures alone are not sufficient for accurately predicting PFM patterns for individual subjects.

Effects of pitch and spatial separation on selective attention in anechoic and reverberant environments

Subjects identified a random, spoken sequence of five monotonized digits (F0 = 100 Hz) presented from 0° azimuth. A monotonized masking sentence (F0 = 84, 89, 94, 100, 106, 112, or 119 Hz) was presented simultaneously from either 0° and +90° azimuth (chosen randomly on each trial). The same talker recorded both target and masker speech. KEMAR-derived transfer functions simulated either a reverberant or anechoic environment. In contrast to previous studies, in the anechoic condition, differences in pitch provided little benefit and differences in location gave improvements explainable by improvements in the target-to- masker ratio at the acoustically better ear. In reverberant conditions, differences in target and masker location improved performance more than differences in pitch; however, performance was best when there were differences in both location and pitch. Results suggest that when a target utterance is easy to segregate and select (such as in anechoic space when the target is a digit sequence embedded in a competing sentence), high-level attributes such as pitch and location do not improve the ability to selectively attend in a speech-on-speech task. However, in more challenging, reverberant conditions, location and pitch cues can aid segregation and/or selection.

Selective spatial attention in a dynamic cocktail party task: Evidence for a strategy based on masker minimization

In cocktail-party listening tasks with multiple spatially separated talkers, it is not clear whether the performance advantages of spatial separation are the result of a target-max strategy, where the listener uses selective attention to enhance sensitivity at the location of the target, or a masker-min strategy, where the listener selectively suppresses sensitivity at the locations of the maskers. In this experiment, listeners were asked to attend to a randomly moving CRM target phrase that was masked by two independently moving CRM masking phrases. The competing signals were lateralized solely on the basis of ITD, and they were band-pass filtered into non-overlapping bands to minimize the effects of energetic masking. The results of the experiments showed (1) that listeners were much more sensitive to changes in the masker locations than to changes in the target location; (2) that listeners consistently performed worse when the two maskers were spatially separated than when they were co-located, even when the average separation between the target and the maskers increased; and (3) that spatial separation of the second masker provided almost no benefit when the first masker was co-located with the target speech. These results seem to provide general support for the masker-min theory of auditory spatial attention.

Evidence for active suppression of masker locations in spatially separated multitalker conditions

Three experiments tested active suppression of masker locations. Using a nonword corpus, spatial release from masking (SRfM) of 3.1 dB was calculated using masked thresholds (67%) of colocated and separated (20 deg) masker and target. Mirrored conditions were completed, with results pooled between hemispheres. In experiment 1, 80% of trials were masked 20 deg left of the central target. Random (10%) trials played targets at the expected masker location, and (10%) at the symmetrically opposite side, with maskers 20 deg laterally displaced. Thresholds revealed 2.6‐dB reduction at the masker location compared to symmetrically opposite (null) locations. Experiment 2 used a central target with masker played 20 deg to the left in 80% of trials. Random (20%) trials (unexpected) played the masker at the symmetrically opposite side. Target thresholds were reduced by 2.1 dB when masker location was unexpected. Both experiments indicate active suppression of expected masker locations, suggesting masker suppression m...

Precedence-based speech segregation in a virtual auditory environment

When a masking sound is spatially separated from a target speech signal, substantial releases from masking typically occur both for speech and noise maskers. However, when a delayed copy of the masker is also presented at the location of the target speech (a condition that has been referred to as the front target, right-front masker or F-RF configuration), the advantages of spatial separation vanish for noise maskers but remain substantial for speech maskers. This effect has been attributed to precedence, which introduces an apparent spatial separation between the target and masker in the F-RF configuration that helps the listener to segregate the target from a masking voice but not from a masking noise. In this study, virtual synthesis techniques were used to examine variations of the F-RF configuration in an attempt to more fully understand the stimulus parameters that influence the release from masking obtained in that condition. The results show that the release from speech-on-speech masking caused by the addition of the delayed copy of the masker is robust across a wide variety of source locations, masker locations, and masker delay values. This suggests that the speech unmasking that occurs in the F-RF configuration is not dependent on any single perceptual cue and may indicate that F-RF speech segregation is only partially based on the apparent left-right location of the RF masker.