The Acoustic Change Complex in Response to Frequency Changes and Its Correlation to Cochlear Implant Speech Outcomes

One of the biggest challenges that face cochlear implant (CI) users is the highly variable hearing outcomes of implantation across patients. Since speech perception requires the detection of various dynamic changes in acoustic features (e.g., frequency, intensity, timing) in speech sounds, it is critical to examine the ability to detect the within-stimulus acoustic changes in CI users. The primary objective of this study was to examine the auditory event-related potential (ERP) evoked by the within-stimulus frequency changes (F-changes), one type of the acoustic change complex (ACC), in adult CI users, and its correlation to speech outcomes. Twenty-one adult CI users (29 individual CI ears) were tested with psychoacoustic frequency change detection tasks, speech tests including the Consonant-Nucleus-Consonant (CNC) word recognition, Arizona Biomedical Sentence Recognition in quiet and noise (AzBio-Q and AzBio-N), and the Digit-in-Noise (DIN) tests, and electroencephalographic (EEG) recordings. The stimuli for the psychoacoustic tests and EEG recordings were pure tones at three different base frequencies (0.25, 1, and 4 kHz) that contained a F-change at the midpoint of the tone. Results showed that the frequency change detection threshold (FCDT), ACC N1′ latency, and P2′ latency did not differ across frequencies (p > 0.05). ACC N1′-P2 amplitude was significantly larger for 0.25 kHz than for other base frequencies (p < 0.05). The mean N1′ latency across three base frequencies was negatively correlated with CNC word recognition (r = −0.40, p < 0.05) and CNC phoneme (r = −0.40, p < 0.05), and positively correlated with mean FCDT (r = 0.46, p < 0.05). The P2′ latency was positively correlated with DIN (r = 0.47, p < 0.05) and mean FCDT (r = 0.47, p < 0.05). There was no statistically significant correlation between N1′-P2′ amplitude and speech outcomes (all ps > 0.05). Results of this study indicated that variability in CI speech outcomes assessed with the CNC, AzBio-Q, and DIN tests can be partially explained (approximately 16–21%) by the variability of cortical sensory encoding of F-changes reflected by the ACC.

The Effect of Nonlinear Frequency Compression on Acoustic Change Complex Responses in High-Frequency Dead-Regioned Hearing Loss

Purpose The study is concern with the distinguishing of the stimuli containing high frequency information with the frequency compression feature at the cortical level using the acoustic change complex (ACC) and the comparison of such with the ACC answers of individuals with normal hearing. Research Design This is a case–control study. Study Sample Thirty adults (21 males and nine females) with normal hearing, ranging in age between 16 and 63 years (mean: 36.7 ± 12.9 years) and 20 adults (16 males and four females) with hearing loss ranging in age between 16 and 70 years (mean:49.0 ± 19.8 years) have been included in this study. Data Collection and Analysis A total of 1,000 ms long stimulus containing 500 and 4,000 Hz tonal stimuli was used for ACC recording. The start frequency (SF) and compression ratio (CR) parameters of the hearing aids were programmed according to the default settings (SFd, CRd) in the device software, the optimal setting (SFo, CRo), and the extra compression (SFe, CRe) requirements and ACC has been recorded for each condition. Evaluation has been performed according to P1-N1-P2 wave complex and ACC complex wave latencies. Independent samples t-test was used to test the significance of the differences between the groups. Results In all individuals ACC has been observed. There was a significant difference between the wave latencies in normal hearing- and hearing-impaired groups. All wave latency averages of the individuals with hearing impairment were longer than the individuals with normal hearing. There were statistically significant differences between SFd-SFo, SFd-SFe, and SFo-SFe parameters. But there was no difference between CRd, CRo, and CRe in terms of CRs. Conclusion In order to discriminate high frequency information at the cortical level we should not rely on default settings of the SF and CR of the hearing aids. Optimal bandwidth must be adjusted without performing insufficient compression or over-compression. ACC can be used besides the real ear measurement for hearing aid fitting.

Utility of Acoustic Change Complex as an Objective Tool to Evaluate Difference Limen for Intensity in Cochlear Hearing Loss and Auditory Neuropathy Spectrum Disorder

Purpose This study aimed to investigate usefulness of acoustic change complex (ACC) as an objective measure of difference limen for intensity (DLI) in auditory neuropathy spectrum disorders (ANSD) and cochlear hearing loss (CHL). Method The study used a multiple static group comparison research design. Twenty normal-hearing individuals (NH), 19 individuals with ANSD, and 23 individuals with CHL underwent DLI measurement using behavioral (psychoacoustic) techniques and ACC. For eliciting ACC, a 500-ms, 1,000-Hz pure tone was presented at 80 dB SPL. Additionally, six variants of this stimulus with intensity increments of 1, 3, 4, 5, 10, and 20 dB starting 250 ms after stimulus onset were used to elicit the ACC. Results The lowest intensity change that produced replicable and clearly identifiable ACC was referred as objective DLI. In comparison to NH and CHL, the behavioral as well as the objective DLI were significantly larger (poorer) in ANSD ( p < .05). Significantly strong positive correlation existed between DLI obtained using behavioral and objective measures ( p < .05). Conclusions ACC could be a useful objective tool to measure DLI in the clinical population, provided the individuals of the clinical population fulfill the prerequisite of the presence of Auditory Long Latency Responses. Supplemental Material https://doi.org/10.23641/asha.12560132

Relation between cortical auditory evoked potentials and behavioral auditory discrimination in cochlear implant children

Background Cochlear implants (CI) can partially or totally revert the effects of sensory deprivation; thus enabling the development of auditory abilities. However, there remains a large amount of variability in speech perception outcome among CI users. Such variability may be attributed to the children’s diverse capabilities in detecting amplitude, temporal and spectral changes in the incoming complex speech signals in quiet and in difficult listening situations. Objective To study whether the newly introduced Acoustic Change Complex (ACC) cortical potential using short duration can be used to document such variability. If used as a tool for cortical discrimination, it will aid in evaluating young children who cannot be tested using behavioral measures. Patients and Methods Cortical auditory evoked potentials were recorded in forty five unilaterally-implanted children ranging in age from 6 to 12 years. Stimuli used to elicit ACC were short duration (500 msec.) speech and tonal stimuli. Spectral change was done using /i/ to /u/ vowels, while temporal change was done using variable gaps-in-1000 Hz tone, ranging from 5 msec. to 200 msec. Auditory evoked responses were compared to behavioral tests which included speech perception test (PBKG) and psychophysical test for temporal resolution. Results ACC potentials were successfully recorded in most of the children evaluated. Generally, ACC were significantly highly detected in temporal changes than spectral change. Individual data showed that poor behavioral performance was associated with higher ACC detection thresholds to gap in tone and poorer % detection to vowel change. Conclusion: ACC potential using short duration stimuli can be recorded in young implanted children in an ordinary clinical setting. However, more research is needed to document the complex behavioral-objective relationship and its ultimate link to speech perception and language development in young CI recipients.

Development of neural perceptual vowel spaces during the first year of life

This study measured infants’ neural responses for spectral changes between all pairs of a set of English vowels. In contrast to previous methods that only allow for the assessment of a few phonetic contrasts, we present a new method that allows us to assess changes in spectral sensitivity across the entire vowel space and create two-dimensional perceptual maps of the infants’ vowel development. Infants aged four to eleven months were played long series of concatenated vowels, and the neural response to each vowel change was assessed using the Acoustic Change Complex (ACC) from EEG recordings. The results demonstrated that the youngest infants’ responses more closely reflected the acoustic differences between the vowel pairs and reflected higher weight to first-formant variation. Older infants had less acoustically driven responses that seemed a result of selective increases in sensitivity for phonetically similar vowels. The results suggest that phonetic development may involve a perceptual warping for confusable vowels rather than uniform learning, as well as an overall increasing sensitivity to higher-frequency acoustic information.