OBJECTIVE: Evaluate sound localization accuracy of subjects with single-sided deafness (SSD) with active transcutaneous bone conduction implants (atBCIs).
METHODS: Prospective case-control study.
METHODS: Tertiary referral center.
METHODS: Ten SSD patients (with ATBCIS) and 10 controls.
METHODS: Localization was assessed in a semianechoic chamber using a 24-speaker array. Stimuli included broadband noise (BBN) and narrowband noise (NBN). Perceived stimulus angle was recorded and compared with presented location. Statistical analyses were performed using ANOVA and Wilcoxon rank sum tests.
METHODS: The primary outcome measures were as follows: 1) mean angular error (MAE) error (°) and regression slope and 2) subjective benefit assessment (Speech Spatial Qualities questionnaire).
RESULTS: Subjects with SSD demonstrated worse localization by MAE and regression slope compared with controls for both broadband noise (p < 0.0001) and narrowband noise at 500 Hz and 1000 kHz (p < 0.0001). There was no statistically significant difference (p = 0.1090) in slope between all groups at 4000 Hz. There was no significant difference in slope or MAE aided compared with unaided. Localization ability varied widely within the SSD cohort, with some individuals showing some ability in the unaided condition, best at 4000 Hz. Although SSQ confirmed particular difficulty in the spatial hearing domain, all domains improved with device use.
CONCLUSIONS: Localization ability for individuals with SSD falls into a somewhat bimodal distribution. Some have fair localization, particularly at high frequencies, that is preserved but not improved with the atBCI. Others have minimal to no localization ability at any frequency, with no apparent device benefit.

OBJECTIVE: To assess the influence of three factors using retrospective chart review: age at which 2nd cochlear implant (CI) is implanted, prior hearing aid (HA) experience in the 2nd CI ear, and long-term experience with bilateral cochlear implants (BICIs) on sound localization in children with sequential BICIs.
METHODS: Mean absolute error (MAE) in localizing speech noise of 60 children with sequential BICIs was compared across four age groups of the 2nd CI (1-5.0; 5.1-10.0; 10.1-14.0; & 14.1-19.0 years) and two extents of prior HA experience (more than and less than one year). MAE was also longitudinally analyzed after 4-6 years of experience with BICI involving 18 participants out of 60.
RESULTS: Children who received 2nd CI before five years of age demonstrated significantly better localization than those who received it after ten years of age. More than one year of prior HA experience in the 2nd CI ear and extensive experience with sequential BICIs significantly enhanced localization performance. Inter-implant intervals and age at the 2nd CI showed a significant positive correlation with the MAE (poorer localization).
CONCLUSIONS: The results indicate that age at 2nd CI is important in developing sound localization skills. Based on the results, obtaining 2nd CI within the first five years of life and no later than ten years old is recommended. The results also suggest that longer use of amplification before 2nd CI and prolonged BICI experience significantly fosters localization development.

This study investigated sound localization abilities in patients with bilateral conductive and/or mixed hearing loss (BCHL) when listening with either one or two middle ear implants (MEIs). Sound localization was measured by asking patients to point as quickly and accurately as possible with a head-mounted LED in the perceived sound direction. Loudspeakers, positioned around the listener within a range of +73°/-73° in the horizontal plane, were not visible to the patients. Broadband (500 Hz-20 kHz) noise bursts (150 ms), roved over a 20-dB range in 10 dB steps was presented. MEIs stimulate the ipsilateral cochlea only and therefore the localization response was not affected by crosstalk. Sound localization was better with bilateral MEIs compared with the unilateral left and unilateral right conditions. Good sound localization performance was found in the bilaterally aided hearing condition in four patients. In two patients, localization abilities equaled normal hearing performance. Interestingly, in the unaided condition, when both devices were turned off, subjects could still localize the stimuli presented at the highest sound level. Comparison with data of patients implanted bilaterally with bone-conduction devices, demonstrated that localization abilities with MEIs were superior. The measurements demonstrate that patients with BCHL, using remnant binaural cues in the unaided condition, are able to process binaural cues when listening with bilateral MEIs. We conclude that implantation with two MEIs, each stimulating only the ipsilateral cochlea, without crosstalk to the contralateral cochlea, can result in good sound localization abilities, and that this topic needs further investigation.

The perception of a talker\'s head orientation is an ecologically relevant task. Humans are able to discriminate changes in talker head orientation using acoustic cues. Factors that may influence measures of this ability have not been well characterized. Here, we examined the minimum audible change in head orientation cues (MACHO) using diotic stimuli. The effects of several factors were tested: talker and gender, stimulus bandwidth (full-band vs low-pass filtered at 8 or 10 kHz), transducer (loudspeaker vs headphone), stimulus uncertainty (interleaved vs blocked presentation of four talkers), and vocal production mode (speech vs singing). The best performance of ∼41° was achieved for full-band, blocked presentation of speech over a loudspeaker. Greater stimulus uncertainty (interleaved presentation) worsened the MACHO by 26%. Bandlimiting at 8 and 10 kHz worsened performance by an additional 22% and 14%, respectively. At equivalent overall sound levels, performance was better for speech than for singing. There was some limited evidence for the transducer influencing the MACHO. These findings suggest the MACHO relies on multiple factors manipulated here. One of the largest, consistent effects was that of talker, suggesting head orientation cues are highly dependent on individual talker characteristics. This may be due to individual variability in speech directivity patterns.

Affective stimuli in our environment indicate reward or threat and thereby relate to approach and avoidance behavior. Previous findings suggest that affective stimuli may bias visual perception, but it remains unclear whether similar biases exist in the auditory domain. Therefore, we asked whether affective auditory voices (angry vs. neutral) influence sound distance perception. Two VR experiments (data collection 2021-2022) were conducted in which auditory stimuli were presented via loudspeakers located at positions unknown to the participants. In the first experiment (N = 44), participants actively placed a visually presented virtual agent or virtual loudspeaker in an empty room at the perceived sound source location. In the second experiment (N = 32), participants were standing in front of several virtual agents or virtual loudspeakers and had to indicate the sound source by directing their gaze toward the perceived sound location. Results in both preregistered experiments consistently showed that participants estimated the location of angry voice stimuli at greater distances than the location of neutral voice stimuli. We discuss that neither emotional nor motivational biases can account for these results. Instead, distance estimates seem to rely on listeners\' representations regarding the relationship between vocal affect and acoustic characteristics. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The neurological basis for perceptual awareness remains unclear, and theories disagree as to whether sensory cortices per se generate awareness. Critically, neural activity in the sensory cortices is only a neural correlate of consciousness (NCC) if it closely matches the contents of perceptual awareness. Research in vision and touch suggest that contralateral activity in sensory cortices is an NCC. Similarly, research in hearing with two sound sources (left and right) presented over headphones also suggests that a candidate NCC called the auditory awareness negativity (AAN) matches perceived location of sound. The current study used 13 different sound sources presented over loudspeakers for natural localization cues and measured event-related potentials to a threshold stimulus in a sound localization task. Preregistered Bayesian mixed models provided moderate evidence against an overall AAN and very strong evidence against its lateralization. Because of issues regarding data quantity and quality, exploratory analyses with aggregated data from multiple loudspeakers were conducted. Results provided moderate evidence for an overall AAN and strong evidence against its lateralization. Nonetheless, the interpretations of these results remain inconclusive. Therefore, future research should reduce the number of conditions and/or test over several sessions to procure a sufficient amount of data. Taken at face value, the results may suggest issues with AAN as an NCC of auditory awareness, as it does not laterally map onto experiences in a free-field auditory environment, in contrast to the NCCs of vision and touch.

Sound-source localization is based on spatial cues arising due to interactions of sound waves with the torso, head and ears. Here, we evaluated neural responses to free-field sound sources in the central nucleus of the inferior colliculus (CIC), the medial geniculate body (MGB) and the primary auditory cortex (A1) of Mongolian gerbils. Using silicon probes we recorded from anaesthetized gerbils positioned in the centre of a sound-attenuating, anechoic chamber. We measured rate-azimuth functions (RAFs) with broad-band noise of varying levels presented from loudspeakers spanning 210° in azimuth and characterized RAFs by calculating spatial centroids, Equivalent Rectangular Receptive Fields (ERRFs), steepest slope locations and spatial-separation thresholds. To compare neuronal responses with behavioural discrimination thresholds from the literature we performed a neurometric analysis based on signal-detection theory. All structures demonstrated heterogeneous spatial tuning with a clear dominance of contralateral tuning. However, the relative amount of contralateral tuning decreased from the CIC to A1. In all three structures spatial tuning broadened with increasing sound-level. This effect was strongest in CIC and weakest in A1. Neurometric spatial-separation thresholds compared well with behavioural discrimination thresholds for locations directly in front of the animal. Our findings contrast with those reported for another rodent, the rat, which exhibits homogenous and sharply delimited contralateral spatial tuning. Spatial tuning in gerbils resembles more closely the tuning reported in A1 of cats, ferrets and non-human primates. Interestingly, gerbils, in contrast to rats, share good low-frequency hearing with carnivores and non-human primates, which may account for the observed spatial tuning properties.

When individuals are exposed to two pure tones with close frequencies presented separately in each ear, they perceive a third sound known as binaural beats (BB), characterized by a frequency equal to the difference between the two tones. Previous research has suggested that BB may influence brain activity, potentially benefiting attention and relaxation. In this study, we hypothesized that the impact of BB on cognition and EEG is linked to the spatial characteristics of the sound. Participants listened to various types of spatially moving sounds (BB, panning and alternate beeps) at 6Hz and 40Hz frequencies. EEG measurements were conducted throughout the auditory stimulation, and participants completed questionnaires on relaxation, affect, and a sustained attention task. The results indicated that binaural, panning sounds and alternate beeps had a more pronounced effect on electrical brain activity than the control condition. Additionally, an improvement in relaxation was observed with these sounds at both 6Hz and 40Hz. Overall, these findings support our hypothesis that the impact of auditory stimulation lies in the spatial attributes rather than the sensation of beating itself.

OBJECTIVE: Acoustic localization accuracy metrics currently employed in clinical literature both overestimate and underestimate performance benefit of cochlear implantation (CI) for single-sided deafness (SSD).
BACKGROUND: Although localization in SSD with CI has been investigated, performance characterization has relied heavily on average error. Although attractively concise, this measure may misrepresent performance. Here, we characterize frequency-specific localization on a granular level in subjects with CI for SSD as a critical analysis of localization outcome metrics.
METHODS: Eight CI recipients with SSD were recruited. Stimuli of broadband (BBN) and narrowband noise (NBN) at low (500 Hz), mid (1000 Hz), and high (4000 Hz) frequencies were presented in a semianechoic chamber. Localization accuracy was quantified in mean angular error (MAE) and linear regression slope.
RESULTS: Use of a CI for SSD subjects improved localization performance by slope for all stimuli ( p ≤ 0.0033) to a level that was equal to normal-hearing controls at 1 and 4 kHz ( p ≥ 0.2281). MAE was also significantly improved for SSD subjects using CI for BBN stimuli ( p ≪ 0.0001); however, no statistically significant improvement in MAE was seen for NBN ( p ≥ 0.5773) with CI use. Descriptive analysis of individual subject performance highlights the reasons for contradictory results.
CONCLUSIONS: There is inherent challenge in characterizing localization benefit for individuals with CI for SSD. Our data demonstrate the limitations of utilization of average error as the sole metric for outcome benefit. We emphasize the importance of continued research investigating alternative outcome measures as we work toward a more refined understanding of the potential benefits and limitations of cochlear implantation for SSD.

Musicians perform better than non-musicians on a variety of non-musical sound-perception tasks. Whether that musicians\' advantage extends to spatial hearing is a topic of increasing interest. Here we investigated one facet of that topic by assessing musicians\' and non-musicians\' sensitivity to the two primary cues to sound-source location on the horizontal plane: interaural-level-differences (ILDs) and interaural-time-differences (ITDs). Specifically, we measured discrimination thresholds for ILDs at 4 kHz (n =246) and ITDs at 0.5 kHz (n = 137) in participants whose musical-training histories covered a wide range of lengths, onsets, and offsets. For ILD discrimination, when only musical-training length was considered in the analysis, no musicians\' advantage was apparent. However, when thresholds were compared between subgroups of non-musicians (<2 years of training) and extreme musicians (≥10 years of training, started ≤ age 7, still playing) a musicians\' advantage emerged. Threshold comparisons between the extreme musicians and other subgroups of highly trained musicians (≥10 years of training) further indicated that the advantage required both starting young and continuing to play. In addition, the advantage was larger in males than in females, by some measures, and was not evident in an assessment of learning. For ITD discrimination, in contrast to ILD discrimination, parallel analyses revealed no apparent musicians\' advantage. The results suggest that musicianship is associated with greater sensitivity to ILDs, a fundamental sound-localization cue, even though that sensitivity is not central to music, that this musicians\' advantage arises, at least in part, from nurture, and that it is governed by a neural substrate where ILDs are processed separately from, and more malleably than, ITDs.