The Effect of Stimulus Intensity and Carrier Frequency on Auditory Middle- and Long-Latency Evoked Potentials Using a Steady-State-Response Approach.

PURPOSE: The purpose of this study was to measure magnitude changes of auditory steady-state responses (ASSRs) and respective transient middle- and long-latency responses as a function of stimulus intensity and carrier frequency. The literature lacks clear consensus, including relationship to loudness. METHOD: A cohort of 48 adults with normal hearing was examined from a companion study (Tlumak, Durrant, & Delgado, 2015) on effects of aging. ASSRs were elicited by repeated tone-burst stimuli presented at rates of 40 and 0.75 Hz at 3 frequencies and 5 levels of stimulus intensity. The design also permitted scrutiny of any gender bias to the results. RESULTS: Similar to derived transient response findings, ASSR magnitude (harmonic sum) systematically increased with intensity. Input-output function only at 0.75 Hz approximated a log-log linear function. However, slopes fell well below that of doubling of loudness per 10 dB SPL. Results failed to demonstrate significance as a function of carrier frequency and gender for both repetition rates. CONCLUSION: Effects of stimulus intensity, carrier frequency, and gender on ASSRs were similar to those of their transient counterparts. Findings remain disappointing for objective loudness estimation. Results suggest only a clear linkage to the long-latency response and the 0.75-Hz magnitude but require careful consideration of limitations/underlying mechanisms when measuring loudness-related effects.

The Effect of Advancing Age on Auditory Middle- and Long-Latency Evoked Potentials Using a Steady-State-Response Approach.

PURPOSE: The purpose of the study was to objectively detect age-specific changes that occur in equivalent auditory steady-state responses (ASSRs), corresponding to transient middle- and long-latency auditory evoked potentials as a function of repetition rate and advancing age. METHOD: The study included 48 healthy hearing adults who were equally divided into 3 groups by age: 20-39, 40-59, and 60-79 years. ASSRs were recorded at 7 repetition rates from 40 down to 0.75 Hz, elicited by trains of repeated tone burst stimuli. RESULTS: Temporal analysis of middle- and long-latency equivalent ASSRs revealed no appreciable changes in the magnitudes of the response across the age groups. Likewise, the spectral analysis revealed that advancing age did not substantially affect the spectral content of the response at each repetition rate. Furthermore, the harmonic sum was not significantly different across the 3 age groups, between the younger adults versus the combined Older Group Sample 1 and Sample 2, and between the two extreme age groups (i.e., 20-39 vs. 60-79) for the middle- and long-latency equivalent ASSRs. CONCLUSION: Advancing age has no effect on the long-latency equivalent ASSRs; however, aging does affect the middle-latency equivalent ASSRs when the mean age difference is ≥ 40 years.

Unexpected intensity changes in the ear canal during a F(0)-shifted feedback experiment.

Effects of frequency-shifted feedback are typically examined using Eventide Harmonizer Series processors to shift the fundamental frequency (F0) of auditory feedback during vocalizations, eliciting compensatory shifts in speaker F0. Recently, unexpected intensity changes were observed in speakers' ear canals, corresponding with F0 shifts. An investigation revealed that feedback time delays introduced by the processor resulted in phase shifts between feedback and unprocessed voice signals radiating into the ear canal via bone conduction, producing combination waves with gains as high as 6 dB. Shifts of this magnitude potentially alter the interpretation of previously published results and should be controlled in future studies.

Steady-state analysis of auditory evoked potentials over a wide range of stimulus repetition rates: profile in children vs. adults.

OBJECTIVE: Auditory steady-state responses (ASSR) evoked by recurrent brief tones were assessed over a wide range of stimulus repetition rates apropos the traditionally measured obligatory, transient, auditory evoked potentials. Repetition rates of ≤ 10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach, speculated to provide technical advantages/additional information over more traditional transient stimulus-response paradigms. DESIGN: Magnitudes were measured at repetition rates from 0.75 to 80 Hz, using trains of repeated tone-burst stimuli. STUDY SAMPLE: Twelve normal-hearing children and a reference sample of 25 young adults. RESULTS: Results show that response magnitudes were significantly larger in children than adults at repetition rates of ≤ 5 Hz. Magnitudes were largest at the two lowest repetition rates, following the trends expected from the transient auditory evoked potential (AEP) literature. The harmonic sum is proposed as a more appropriate measure of response magnitude than amplitude of the fundamental alone. CONCLUSIONS: The analysis methods used in this paper may give information that will have applications for clinical testing. Of pragmatic importance is that the stimulus rate profile could be determined without subjective wave identification and/or interpretation, and thus by a method that is inherently more objective than conventional AEP analysis.

Steady-state analysis of auditory evoked potentials over a wide range of stimulus repetition rates in awake vs. natural sleep.

OBJECTIVE: Auditory steady-state responses (ASSR) evoked by recurrent tones were assessed over a wide range of stimulus repetition rates embracing well the traditionally measured transient AEPs. Repetition rates of ≤ 10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach which is speculated to provide technical advantages, if not additional/supplemental information, over more traditional transient stimulus-response paradigms. DESIGN: Magnitudes were measured at repetition rates from 0.75 to 80 Hz, using trains of recurrent tone-burst stimuli. STUDY SAMPLE: Twenty-five normal-hearing adults during sleep and awake. RESULTS: Results show that response magnitudes for adults tested during sleep were significantly larger than those for adults while awake at repetition rates <5 Hz. Magnitudes were largest at the two lowest repetition rates, as expected from corresponding results obtained using conventional methods. CONCLUSIONS: The analysis methods used in this paper may give information that will have applications for clinical testing. Results confirm and extend knowledge of the effects of repetition rate on AEPs over a range embracing the gamut of responses as traditionally classified, specifically at the beginning stages of natural sleep.

Steady-state analysis of auditory evoked potentials over a wide range of stimulus repetition rates: profile in adults.

OBJECTIVE: Quasi-steady-state responses were assessed over a wide range of stimulus repetition rates embracing well the traditionally measured transient AEPs (obligatory auditory evoked potentials of all latencies). Repetition rates of ≤10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach which is speculated to provide technical advantages, if not additional information, over more traditional transient stimulus-response paradigms. DESIGN: A measure introduced and defined as the sum of the response at the stimulus frequency and its harmonics. The magnitude of steady-state responses were measured at repetition rates from 0.75 to 80 Hz, using trains of repeated tone-burst stimuli. STUDY SAMPLE: Twenty-five normal-hearing adults. RESULTS: Results show that the magnitudes of the response across repetition rates are largest at the two lowest rates, following trends expected from the transient AEP literature. Good reliability overall was observed for the harmonic sum. CONCLUSIONS: The analysis methods used in this paper may give information that will have application for clinical testing. Of pragmatic importance is that the rate profile could be determined without subjective wave identification and/or interpretation, and thus by a method that is inherently more objective than conventional AEP tests.

Meta-analysis of variables that affect accuracy of threshold estimation via measurement of the auditory steady-state response (ASSR).

Reported are the results of meta-analyses of data derived collectively from a sample of 56 published research studies on electric response audiometry (ERA) using auditory steady-state responses (ASSRs). Several specific methodological issues were examined and hypotheses were posited to rigorously test common conclusions drawn from the ASSR literature on the accuracy of ASSR-ERA. Explanatory variables for analyses were type of population (normally hearing and hearing-impaired), type of modulation, number of sweeps acquired during response analysis, electrode montage, and modulation rate (80 vs. 40 Hz). No explanatory variables were found to be significantly related to the degree of disparity between thresholds obtained by ASSR-ERA versus behavioral audiometry in the normally hearing population. Conversely, all but one explanatory variable (i.e. electrode montage) was found to be significantly related to mean threshold differences in the hearing-impaired and combined populations. Results both substantiate some of common conclusions drawn from the literature but call others into question, helping to identify those methodological issues which appear to, or not to, significantly affect the accuracy of estimating threshold using ASSR measurement. In addition to these findings, another practical outcome of this study was the development of various summary tables of the data analysed from the literature sampled.

80 Hz auditory steady-state responses (ASSR) at 250 Hz and 12,000 Hz.

Although measurement of the detection limits of the 80 Hz auditory steady-state response (ASSR) has proven to be a reasonably reliable tool in estimating hearing sensitivity in the mid-conventional audiometric frequencies (e.g. 1000 and 2000 Hz), results in the literature suggest potentially diminishing performance at 500 Hz and above 4000 Hz. The primary goal of this work was to examine the accuracy of threshold estimation via ASSR measurement for carriers more toward the audiometric extremes. At the same time, different stimulus and recording protocols than those commonly employed in ASSR testing were examined. Using a two-channel recording system, ASSRs were obtained from 15 normal-hearing young adults for an amplitude-modulated carrier of 250 Hz and repeated tone bursts of 10,000-16,000 Hz, gated using a Blackman window. Results attest to the ability to record ASSRs to a wide range of carrier frequencies but also suggest that accuracy of threshold estimation suffers toward the audiometric extremes. Feasibility of ASSR-based high-frequency audiometry is demonstrated in principle, but it is not clear that this method will permit adequate sensitivity and accuracy to support such applications as ototoxicity monitoring.