Automated cortical auditory response detection strategy.

Objective: This study describes a new automated strategy to determine the detection status of an electrophysiological response.Design: Response, noise and signal-to-noise ratio of the cortical auditory evoked potential (CAEP) were characterised. Detection rules were defined: when to start testing, when to conduct subsequent statistical tests using residual noise as an objective criterion, and when to stop testing.Study sample: Simulations were run to determine optimal parameters on a large combined CAEP data set collected in 45 normal-hearing adults and 17 adults with hearing loss.Results: The proposed strategy to detect CAEPs is fully automated. The first statistical test is conducted when the residual noise level is equal to or smaller than 5.1 µV. The succeeding Hotelling's T2 statistical tests are conducted using pre-defined residual noise levels criteria ranging from 5.1 to 1.2 µV. A rule was introduced allowing to stop testing before the maximum number of recorded epochs is reached, depending on a minimum p-value criterion.Conclusion: The proposed framework can be applied to systems which involves detection of electrophysiological responses in biological systems containing background noise. The proposed detection algorithm which optimise sensitivity, specificity, and recording time has the potential to be used in clinical setting.

Is cortical automatic threshold estimation a feasible alternative for hearing threshold estimation with adults with dementia living in aged care?

Objective: This study explored the feasibility of cortical automatic threshold estimation (CATE), a fully automated late auditory evoked potential (AEP) test, as an alternative to pure-tone audiometry for hearing threshold estimation for adults with dementia living in aged care.Design: A single group cross-sectional study was conducted. Participants' dementia severity was determined through the Clinical Dementia Rating scale. Hearing thresholds were obtained for four audiometric frequencies in at least one ear by using both pure-tone audiometry and CATE.Study sample: Sixteen participants enrolled in the study, of which 14 completed at least one of the hearing tests. Twelve ears, from six participants, were included in the final correlation analysis.Results: Pearson correlation coefficients were significant between CATE and pure-tone audiometry for all frequencies: r2 = 0.52 (p = 0.008) for 500 Hz, r2 = 0.79 (p = 0.0001) for 1000 Hz, r2 = 0.71 (p = 0.0005) for 2000 Hz, and r2 = 0.92 (p < 0.0001) for 4000 Hz. Cortical thresholds were within 10 dB of behavioural thresholds for all four frequencies.Conclusions: Findings are encouraging for the feasibility of CATE as an alternative diagnostic test to pure-tone audiometry for adults living with dementia in aged care.

Bigger Is Better: Increasing Cortical Auditory Response Amplitude Via Stimulus Spectral Complexity.

OBJECTIVE: To determine the influence of auditory stimuli spectral characteristics on cortical auditory evoked potentials (CAEPs). DESIGN: CAEPs were obtained from 15 normal-hearing adults in response to six multitone (MT), four pure-tone (PT), and two narrowband noise stimuli. The sounds were presented at 10, 20, and 40 dB above threshold, which were estimated behaviorally beforehand. The root mean square amplitude of the CAEP and the detectability of the response were calculated and analyzed. RESULTS: Amplitudes of the CAEPs to the MT were significantly larger compared with PT for stimuli with frequencies centered around 1, 2, and 4 kHz, whereas no significant difference was found for 0.5 kHz. The objective detection score for the MT was significantly higher compared with the PT. For the 1- and 2-kHz stimuli, the CAEP amplitudes to narrowband noise were not significantly different than those evoked by PT. CONCLUSION: The study supports the notion that spectral complexity, not just bandwidth, has an impact on the CAEP amplitude for stimuli with center frequency above 0.5 kHz. The implication of these findings is that the clinical test time required to estimate thresholds can potentially be decreased by using complex band-limited MT rather than conventional PT stimuli.

Barriers to Adoption of Digital Therapeutics (DTx) into Audiology Clinical Practice: Acknowledging the Challenges, Adapting to the Future.

The continuous advancements in technologies supporting digital health and digital therapeutics (DTx) bring new possibilities to the field of audiology. This study considers a new DTx for tinnitus called Tinnibot and the willingness of a group of Australian university audiology students to consider this new DTx in their future careers as practicing audiologists. A single-group case-series design (pretest/posttest) was used to examine the opinions of 10 university audiology students before and after participating in a 2-hour information workshop on the topics of tinnitus, DTx, cognitive behavioral therapy, and a new digital therapy tool for tinnitus called Tinnibot. Student knowledge levels of the main topic areas increased from poor (before the workshop) to moderate to high after the workshop, with 40% of participants reporting they would very likely use digital therapies for future patients. A common barrier to improving this rating was the need for direct hands-on training on the DTx before the students would be confident to recommend the DTx to patients. Incorporating direct training on DTx into university audiology programs would allow greater uptake of DTx by students as they begin their careers as practicing audiologists.

Acoustic change complex for assessing speech discrimination in normal-hearing and hearing-impaired infants.

OBJECTIVE: This study examined (1) the utility of a clinical system to record acoustic change complex (ACC, an event-related potential recorded by electroencephalography) for assessing speech discrimination in infants, and (2) the relationship between ACC and functional performance in real life. METHODS: Participants included 115 infants (43 normal-hearing, 72 hearing-impaired), aged 3-12 months. ACCs were recorded using [szs], [uiu], and a spectral rippled noise high-pass filtered at 2 kHz as stimuli. Assessments were conducted at age 3-6 months and at 7-12 months. Functional performance was evaluated using a parent-report questionnaire, and correlations with ACC were examined. RESULTS: The rates of onset and ACC responses of normal-hearing infants were not significantly different from those of aided infants with mild or moderate hearing loss but were significantly higher than those with severe loss. On average, response rates measured at 3-6 months were not significantly different from those at 7-12 months. Higher rates of ACC responses were significantly associated with better functional performance. CONCLUSIONS: ACCs demonstrated auditory capacity for discrimination in infants by 3-6 months. This capacity was positively related to real-life functional performance. SIGNIFICANCE: ACCs can be used to evaluate the effectiveness of amplification and monitor development in aided hearing-impaired infants.

Deconvolution of Ears' Activity (DEA): A New Experimental Paradigm to Investigate Central Auditory Processing.

A novel experimental paradigm, "deconvolution of ears' activity" (DEA), is presented which allows to disentangle overlapping neural activity from both auditory cortices when two auditory stimuli are presented closely together in time in each ear. Pairs of multi-tone complexes were presented either binaurally, or sequentially by alternating presentation order in each ear (i.e., first tone complex of the pair presented to one ear and second tone complex to the other ear), using stimulus onset asynchronies (SOAs) shorter than the neural response length. This timing strategy creates overlapping responses, which can be mathematically separated using least-squares deconvolution. The DEA paradigm allowed the evaluation of the neural representation in the auditory cortex of responses to stimuli presented at syllabic rates (i.e., SOAs between 120 and 260 ms). Analysis of the neuromagnetic responses in each cortex offered a sensitive technique to study hemispheric lateralization, ear representation (right vs. left), pathway advantage (contra- vs. ipsi-lateral) and cortical binaural interaction. To provide a proof-of-concept of the DEA paradigm, data was recorded from three normal-hearing adults. Results showed good test-retest reliability, and indicated that the difference score between hemispheres can potentially be used to assess central auditory processing. This suggests that the method could be a potentially valuable tool for generating an objective "auditory profile" by assessing individual fine-grained auditory processing using a non-invasive recording method.

Relationship between objective measures of hearing discrimination elicited by non-linguistic stimuli and speech perception in adults.

Some people using hearing aids have difficulty discriminating between sounds even though the sounds are audible. As such, cochlear implants may provide greater benefits for speech perception. One method to identify people with auditory discrimination deficits is to measure discrimination thresholds using spectral ripple noise (SRN). Previous studies have shown that behavioral discrimination of SRN was associated with speech perception, and behavioral discrimination was also related to cortical responses to acoustic change or ACCs. We hypothesized that cortical ACCs could be directly related to speech perception. In this study, we investigated the relationship between subjective speech perception and objective ACC responses measured using SRNs. We tested 13 normal-hearing and 10 hearing-impaired adults using hearing aids. Our results showed that behavioral SRN discrimination was correlated with speech perception in quiet and in noise. Furthermore, cortical ACC responses to phase changes in the SRN were significantly correlated with speech perception. Audibility was a major predictor of discrimination and speech perception, but direct measures of auditory discrimination could contribute information about a listener's sensitivity to acoustic cues that underpin speech perception. The findings lend support for potential application of measuring ACC responses to SRNs for identifying people who may benefit from cochlear implants.

Cortical Auditory-Evoked Potentials in Response to Multitone Stimuli in Hearing-Impaired Adults.

PURPOSE: To determine if one-octave multitone (MT) stimuli increase the amplitude of cortical auditory-evoked potentials (CAEPs) in individuals with a hearing loss when compared to standard pure-tone (PT) stimuli and narrow-band noise (NBN). RESEARCH DESIGN: CAEPs were obtained from 16 hearing-impaired adults in response to PT and MT auditory stimuli centered around 0.5, 1, 2, and 4 kHz and NBN centered around 1 and 2 kHz. Hearing impairment ranged from a mild to a moderate hearing loss in both ears. Auditory stimuli were monaurally delivered through insert earphones at 10 and 20 dB above threshold. The root mean square amplitude of the CAEP and the detectability of the responses using Hotelling's T² were calculated and analyzed. RESULTS: CAEP amplitudes elicited with MT stimuli were on average 29% larger than PT stimuli for frequencies centered around 1, 2, and 4 kHz. No significant difference was found for responses to 0.5-kHz stimuli. Significantly higher objective detection scores were found for MT when compared to PT. For the 1- and 2-kHz stimuli, the CAEP amplitudes to NBN were not significantly different to those evoked by PT but a significant difference was found between MT stimuli and both NBN and PT. The mean detection sensitivity of MT for the four frequencies was 80% at 10 dB SL and 95% at 20 dB SL, and was comparable with detection sensitivities observed in normal-hearing participants. CONCLUSIONS: Using MT stimuli when testing CAEPs in adults with hearing impairment showed larger amplitudes and a higher objective detection sensitivity compared to using traditional PT stimuli for frequencies centered around 1, 2, and 4 kHz. These findings suggest that MT stimuli are a clinically useful tool to increase the efficiency of frequency-specific CAEP testing in adults with hearing impairment.

Least-squares deconvolution of evoked potentials and sequence optimization for multiple stimuli under low-jitter conditions.

OBJECTIVE: Rapid presentation of stimuli in an evoked response paradigm can lead to overlap of multiple responses and consequently difficulties interpreting waveform morphology. This paper presents a deconvolution method allowing overlapping multiple responses to be disentangled. METHODS: The deconvolution technique uses a least-squared error approach. A methodology is proposed to optimize the stimulus sequence associated with the deconvolution technique under low-jitter conditions. It controls the condition number of the matrices involved in recovering the responses. Simulations were performed using the proposed deconvolution technique. RESULTS: Multiple overlapping responses can be recovered perfectly in noiseless conditions. In the presence of noise, the amount of error introduced by the technique can be controlled a priori by the condition number of the matrix associated with the used stimulus sequence. The simulation results indicate the need for a minimum amount of jitter, as well as a sufficient number of overlap combinations to obtain optimum results. An aperiodic model is recommended to improve reconstruction. CONCLUSIONS: We propose a deconvolution technique allowing multiple overlapping responses to be extracted and a method of choosing the stimulus sequence optimal for response recovery. SIGNIFICANCE: This technique may allow audiologists, psychologists, and electrophysiologists to optimize their experimental designs involving rapidly presented stimuli, and to recover evoked overlapping responses.

Deconvolution of overlapping cortical auditory evoked potentials recorded using short stimulus onset-asynchrony ranges.

OBJECTIVE: The first aim of this study is to validate the theoretical framework of least-squares (LS) deconvolution on experimental data. The second is to investigate the waveform morphology of the cortical auditory evoked potential (CAEP) for five stimulus onset-asynchronies (SOAs) and effects of alternating stimulus frequency in normally hearing adults. METHODS: Eleven adults (19-55 years) with normal hearing were investigated using tone-burst stimuli of 500 and 2000 Hz with SOAs jittered around 150, 250, 450, and 850 ms in a paired-interval paradigm with fixed or alternating stimulus frequency. RESULTS: The LS deconvolution technique disentangled the overlapping responses, which then provided the following insights. The CAEP amplitude reached a minimum value for SOAs jittered around 450 ms, in contrast with significantly larger amplitudes for SOAs jittered around 150 and 850 ms. Despite this, longer latencies of N1 and P2 consistently occurred for decreasing SOAs. Alternating stimulus frequency significantly increased the amplitude of the CAEP response and decreased latencies for SOAs jittered around 150 ms. Effects of SOAs and alternating stimuli on CAEP amplitude can be modelled using a quantitative model of latent inhibition. CONCLUSIONS: LS deconvolution allows correction for cortical response overlap. The amplitude of the CAEP is sensitive to SOA and stimulus frequency alternation. SIGNIFICANCE: CAEPs are emerging as an important tool in the objective evaluation of hearing aid and cochlear implant fittings. Responses to closely spaced stimuli provide objective information about integration and inhibition mechanisms in the auditory cortex.

Deconvolution of magnetic acoustic change complex (mACC).

OBJECTIVE: The aim of this study was to design a novel experimental approach to investigate the morphological characteristics of auditory cortical responses elicited by rapidly changing synthesized speech sounds. METHODS: Six sound-evoked magnetoencephalographic (MEG) responses were measured to a synthesized train of speech sounds using the vowels /e/ and /u/ in 17 normal hearing young adults. Responses were measured to: (i) the onset of the speech train, (ii) an F0 increment; (iii) an F0 decrement; (iv) an F2 decrement; (v) an F2 increment; and (vi) the offset of the speech train using short (jittered around 135ms) and long (1500ms) stimulus onset asynchronies (SOAs). The least squares (LS) deconvolution technique was used to disentangle the overlapping MEG responses in the short SOA condition only. RESULTS: Comparison between the morphology of the recovered cortical responses in the short and long SOAs conditions showed high similarity, suggesting that the LS deconvolution technique was successful in disentangling the MEG waveforms. Waveform latencies and amplitudes were different for the two SOAs conditions and were influenced by the spectro-temporal properties of the sound sequence. The magnetic acoustic change complex (mACC) for the short SOA condition showed significantly lower amplitudes and shorter latencies compared to the long SOA condition. The F0 transition showed a larger reduction in amplitude from long to short SOA compared to the F2 transition. Lateralization of the cortical responses were observed under some stimulus conditions and appeared to be associated with the spectro-temporal properties of the acoustic stimulus. CONCLUSIONS: The LS deconvolution technique provides a new tool to study the properties of the auditory cortical response to rapidly changing sound stimuli. The presence of the cortical auditory evoked responses for rapid transition of synthesized speech stimuli suggests that the temporal code is preserved at the level of the auditory cortex. Further, the reduced amplitudes and shorter latencies might reflect intrinsic properties of the cortical neurons to rapidly presented sounds. SIGNIFICANCE: This is the first demonstration of the separation of overlapping cortical responses to rapidly changing speech sounds and offers a potential new biomarker of discrimination of rapid transition of sound.

Least-squares (LS) deconvolution of a series of overlapping cortical auditory evoked potentials: a simulation and experimental study.

OBJECTIVE: To evaluate the viability of disentangling a series of overlapping 'cortical auditory evoked potentials' (CAEPs) elicited by different stimuli using least-squares (LS) deconvolution, and to assess the adaptation of CAEPs for different stimulus onset-asynchronies (SOAs). APPROACH: Optimal aperiodic stimulus sequences were designed by controlling the condition number of matrices associated with the LS deconvolution technique. First, theoretical considerations of LS deconvolution were assessed in simulations in which multiple artificial overlapping responses were recovered. Second, biological CAEPs were recorded in response to continuously repeated stimulus trains containing six different tone-bursts with frequencies 8, 4, 2, 1, 0.5, 0.25 kHz separated by SOAs jittered around 150 (120-185), 250 (220-285) and 650 (620-685) ms. The control condition had a fixed SOA of 1175 ms. In a second condition, using the same SOAs, trains of six stimuli were separated by a silence gap of 1600 ms. Twenty-four adults with normal hearing (<20 dB HL) were assessed. MAIN RESULTS: Results showed disentangling of a series of overlapping responses using LS deconvolution on simulated waveforms as well as on real EEG data. The use of rapid presentation and LS deconvolution did not however, allow the recovered CAEPs to have a higher signal-to-noise ratio than for slowly presented stimuli. The LS deconvolution technique enables the analysis of a series of overlapping responses in EEG. SIGNIFICANCE: LS deconvolution is a useful technique for the study of adaptation mechanisms of CAEPs for closely spaced stimuli whose characteristics change from stimulus to stimulus. High-rate presentation is necessary to develop an understanding of how the auditory system encodes natural speech or other intrinsically high-rate stimuli.