Acoustic Change Complex Evoked by Horizontal Sound Location Change in Young Adults With Normal Hearing

Clinical programming can limit access to binaural cues in children with bilateral cochlear implants

OBJECTIVE

In children with bilateral cochlear implants(CIs): 1) quantify cortical access and sensitivity to inter-aural level differences(ILDs); 2) determine if cortical ILD detection predicts ILD perception; and 3) assess demographic and clinical factors that could limit ILD access.

METHODS

Cortical detection responses evoked by ILD changes were measured in 22/24 children with bilateral CIs(7 female) using their clinically programmed devices and in 8 children(3 female) with normal hearing. Behavioral lateralization(left vs right perception) to ILDs was also measured.

RESULTS

Increased cortical sensitivity(amplitude) to ILD changes did not predict more accurate behavioral perception; rather children with CIs were able to lateralize ILDs with fair accuracy but with increased cognitive effort(reaction times) compared to normal hearing children (p = 0.0004, Cohen's d = 1.17). While demographic factors did not significantly contribute to response measures, symmetry of programmed levels in the left and right CIs predicted better cortical and behavioral sensitivity to ILDs (ps < 0.05).

CONCLUSIONS

the developing auditory system can detect ILD cues when provided with bilateral cochlear implants; however, this access can be altered by programming and may not translate to normal binaural processing.

SIGNIFICANCE

There is potential for clinical programming to improve spatial hearing in children with bilateral CIs.

The Performance of the Acoustic Change Complex Versus Psychophysical Behavioral Measures: A Systematic Review of Measurements in Adults

OBJECTIVES

The acoustic change complex (ACC) is a cortical auditory evoked potential that shows promise as an objective test of the neural capacity for speech and sound discrimination, particularly for difficult-to-test populations, for example, cognitively impaired adults. There is uncertainty, however, surrounding the performance of the ACC with behavioral measures. The objective of this study was to systematically review the literature, focusing on adult studies, to investigate the relationship between ACC responses and behavioral psychophysical measures.

DESIGN

Original peer-reviewed articles conducting performance comparisons between ACCs and behavioral measures in adults were identified through systematic searches. The review was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for reporting, and the methodological quality of the included articles was assessed.

RESULTS

A total of 66 studies were retrieved that conducted adult ACC measurements, of which 27 studies included performance comparisons. Meta-analysis revealed a total of 41 significant correlations between ACC responses (amplitudes, latencies, and thresholds) and behavioral measures of speech perception (2 weak, 28 moderate, and 11 strong correlations), and 12 significant moderate/strong correlations were identified with behavioral measures of frequency discrimination.

CONCLUSIONS

This systematic review finds that ACC responses are associated with speech perception and frequency discrimination, in addition to other types of sound discrimination. The choice of evoking stimuli, ACC outcome measure, and behavioral measure used may influence the strength and visibility of potential correlations between the objective (ACC) and behavioral measures. The performance of the ACC technique highlighted in this review suggests that this tool may serve as an alternative measure of auditory discrimination when corresponding behavioral measures prove challenging or unfeasible.

Neural encoding for spatial release from informational masking and its correlation with behavioral metrics

The central auditory system encompasses two primary functions: identification and localization. Spatial release from masking (SRM) highlights speech recognition in competing noise and improves the listening experience when a spatial cue is introduced between noise and target speech. This assessment focuses on the integrity of auditory function and holds clinical significance. However, infants or pre-lingual subjects sometimes provide less reliable results. This study investigates the value of cortical auditory evoked potentials (CAEPs) onset and acoustic change complex (ACC) as an objective measurement of SRM. Thirty normal-hearing young adults (11 males) were recruited. We found the spatial separation of signals and noise (±90° symmetrically) resulted in a signal-to-noise ratio (SNR) improvement of 9.00 ± 1.71 dB behaviorally. It significantly enhanced cortical processing at all SNR levels, shortened CAEP latencies, and increased amplitudes, resulting in a greater number of measurable peaks for ACC. SRM showed mild to moderate correlations with the differences between two conditions in CAEP measures. The regression model combining N1'-P2' amplitude at 5 dB SNR (R2 = 0.26), P1 amplitude at 0 dB SNR (R2 = 0.14), and P1 latency at -5 dB SNR (R2 = 0.15), explained 45.3% of the variance in SRM. Our study demonstrates that introducing spatial cues can improve speech perception and enhance central auditory processing in normal-hearing young adults. CAEPs may contribute to predictions about SRM and hold potential for practical application.NEW & NOTEWORTHY The neural encoding of spatial release from masking (SRM) can be observed in normal-hearing young adults. Spatial separation between target and masker improves speech perception in noise and enhances central auditory processing. The behavioral results showed mild-to-moderate correlations with electrophysiological measures, with acoustic change complex (ACC) amplitude being a better indicator than onset components. Cortical auditory evoked potentials (CAEPs) may contribute to predictions about spatial release from masking, especially when behavioral tests are less reliable.

Age-related differences in auditory spatial processing revealed by acoustic change complex

Objectives

The auditory spatial processing abilities mature throughout childhood and degenerate in older adults. This study aimed to compare the differences in onset cortical auditory evoked potentials (CAEPs) and location-evoked acoustic change complex (ACC) responses among children, adults, and the elderly and to investigate the impact of aging and development on ACC responses.

Design

One hundred and seventeen people were recruited in the study, including 57 typically-developed children, 30 adults, and 30 elderlies. The onset-CAEP evoked by white noise and ACC by sequential changes in azimuths were recorded. Latencies and amplitudes as a function of azimuths were analyzed using the analysis of variance, Pearson correlation analysis, and multiple linear regression model.

Results

The ACC N1'-P2' amplitudes and latencies in adults, P1'-N1' amplitudes in children, and N1' amplitudes and latencies in the elderly were correlated with angles of shifts. The N1'-P2' and P2' amplitudes decreased in the elderly compared to adults. In Children, the ACC P1'-N1' responses gradually differentiated into the P1'-N1'-P2' complex. Multiple regression analysis showed that N1'-P2' amplitudes (R2 = 0.33) and P2' latencies (R2 = 0.18) were the two most variable predictors in adults, while in the elderly, N1' latencies (R2 = 0.26) explained most variances. Although the amplitudes of onset-CAEP differed at some angles, it could not predict angle changes as effectively as ACC responses.

Conclusion

The location-evoked ACC responses varied among children, adults, and the elderly. The N1'-P2' amplitudes and P2' latencies in adults and N1' latencies in the elderly explained most variances of changes in spatial position. The differentiation of the N1' waveform was observed in children. Further research should be conducted across all age groups, along with behavioral assessments, to confirm the relationship between aging and immaturity in objective ACC responses and poorer subjective spatial performance.

Significance

ACCs evoked by location changes were assessed in adults, children, and the elderly to explore the impact of aging and development on these differences.

Temporal integration of sound motion: Motion-onset response and perception

The purpose of our study was to estimate the time interval required for integrating the acoustical changes related to sound motion using both psychophysical and EEG measures. Healthy listeners performed direction identification tasks under dichotic conditions in the delayed-motion paradigm. Minimal audible movement angle (MAMA) has been measured over the range of velocities from 60 to 360 deg/s. We also measured minimal duration of motion, at which the listeners could identify its direction. EEG was recorded in the same group of subjects during passive listening. Motion onset responses (MOR) were analyzed. MAMA increased linearly with motion velocity. Minimum audible angle (MAA) calculated from this linear function was about 2 deg. For higher velocities of the delayed motion, we found 2- to 3-fold better spatial resolution than the one previously reported for motion starting at the sound onset. The time required for optimal discrimination of motion direction was about 34 ms. The main finding of our study was that both direction identification time obtained in the behavioral task and cN1 latency behaved like hyperbolic functions of the sound's velocity. Direction identification time decreased asymptotically to 8 ms, which was considered minimal integration time for the instantaneous shift detection. Peak latency of cN1 also decreased with increasing velocity and asymptotically approached 137 ms. This limit corresponded to the latency of response to the instantaneous sound shift and was 37 ms later than the latency of the sound-onset response. The direction discrimination time (34 ms) was of the same magnitude as the additional time required for motion processing to be reflected in the MOR potential. Thus, MOR latency can be viewed as a neurophysiological index of temporal integration. Based on the findings obtained, we may assume that no measurable MOR would be evoked by slowly moving stimuli as they would reach their MAMAs in a time longer than the optimal integration time.

Physiological evaluations of low-level impulsive sounds generated by an air conditioner

Air conditioners are typically installed in buildings and vehicles to control thermal conditions for long periods of time. Air conditioners generate certain types of sounds while functioning, which are among the main noise sources in buildings and vehicles. Most sounds produced by the air conditioner do not change with time, and the sound quality of steady sounds has been investigated. However, air conditioners can generate low-level impulsive sounds. Customers complain of the discomfort caused when these sounds disturb the silence in their living rooms and bedrooms. This study aimed to determine the physical factors that have a significant effect on physiological responses to low-level impulsive sounds produced by air conditioners. We used physiological responses because it is difficult for people to evaluate sounds psychologically when they are sleeping or are not focused on the sounds. The A-weighted equivalent continuous sound pressure level (L_Aeq) and the factors extracted from the autocorrelation function (ACF) were evaluated as physical factors. Participant responses on electroencephalography (EEG) were evaluated. The correlation between the EEG responses and ACF factors was determined. The L_Aeq, peak, and delay time to the first maximum peak of the ACF were identified as significant factors for physiological responses to low-level impulsive sounds.