Estimating Multiple Latencies in the Auditory System from Auditory Steady-State Responses on a Single EEG Channel

Abstract

The latency of the auditory steady-state response (ASSR) may provide valuable information regarding the integrity of the auditory system, as it could potentially reveal the presence of multiple intracerebral sources. To estimate multiple latencies from recorded ASSRs, we propose a novel two-stage procedure that consists of a nonparametric estimation method, called apparent latency from phase coherence (ALPC), followed by a heuristic sequential forward selection algorithm (SFS). Compared with existing methods, ALPC requires few prior assumptions, and is straightforward to implement for higher-order nonlinear responses to multi-cosine sound complexes with their initial phases set to zero. It systematically evaluates the nonlinear components of the ASSRs by estimating multiple latencies, automatically identifies involved ASSR components, and reports a latency consistency index (LCI). To verify the proposed method, we performed simulations for several scenarios: two nonlinear subsystems with different or overlapping outputs. We also recorded the EEG from ten normal-hearing adults by bilaterally presenting superimposed tones with four frequencies that evoke a unique set of ASSRs. From these ASSRs, two major latencies were found to be stable across subjects on repeated measurement days. The two latencies are dominated by low-frequency (LF) (near 40 Hz, at around 41-52 ms) and high-frequency (HF) (>80 Hz, at around 21-27 ms) ASSR components. The frontal-central (FC) brain region showed longer latencies on LF components, but shorter latencies on HF components, when compared with temporal-lobe regions. In conclusion, the proposed nonparametric ALPC-SFS method, applied to zero-phase, multi-cosine sound complexes is more suitable for evaluating embedded nonlinear systems underlying ASSRs than existing methods. It is thus promising as an objective measure of hearing performance and auditory cortex (dis)function.

Towards Real-Time Detection of Auditory Steady-State Responses: A Comparative Study

“…We applied a three-stage preprocessing protocol on the raw EEG recordings as described in our previous study [5]. First, EEG signals were re-referenced to a common average reference (CAR) after excluding the EEG electrodes above the eyes due to eye-blink and eye-movement artifacts.…”

“…It was found that ASSRs show a general strong activation in the frontal-central brain [36], [5]. Therefore, in this study, to illustrate the real-time detectors, we performed the ASSR detection for all subjects on the same frontal-central brain region (near EEG channel FCz).…”

“…to additional ASSRs. The higher-order ASSRs often cover a larger frequency range and have been used to estimate multiple frequency-related apparent latencies of the auditory system [5]. For a nonlinear system with system order R, given two input frequencies (f 1 and f 2 ), a series of combination frequencies is produced at the output, characterized by nf 1 ± mf 2 (> 0), with n and m positive integers, such that n + m ≤ R [5], [39].…”

“…ASSRs are due to nonlinear signal processes that may be generated at different levels within the auditory pathway, ranging from as early as the cochlear nerve and subcortical sources, to the neocortex [3], [4]. Because of their reproducibility and involuntary nature, ASSRs have been considered a valid objective biomarker to assess hearing thresholds for clinical use and auditory system disorders [3], [5]. This characteristic of ASSRs thus allows objective response detection methods to extract the relatively weak AS-SRs from noisy EEG measurements, by analyzing a number of repetitive trials.…”

“…To validate these detectors, we applied the three real-time detectors to the EEG data from nine normalhearing human subjects. From the results of our earlier study [5], we imposed a measurement time of 12.3 s for each EEG trial to ensure a sufficient frequency resolution. The maximum trial number (i.e., 100) was determined from one pilot measurement (on one subject) to ensure the detection for most of target ASSRs.…”