Estimation of auditory steady-state responses based on the averaging of independent EEG epochs

Abstract

The amplitude of auditory steady-state responses (ASSRs) generated in the brainstem of rats exponentially decreases over the sequential averaging of EEG epochs. This behavior is partially due to the adaptation of the ASSR induced by the continuous and monotonous stimulation. In this study, we analyzed the potential clinical relevance of the ASSR adaptation. ASSR were elicited in eight anesthetized adult rats by 8-kHz tones, modulated in amplitude at 115 Hz. We called independent epochs to those EEG epochs acquired with sufficiently long inter-stimulus interval, so the ASSR contained in any given epoch is not affected by the previous stimulation. We tested whether the detection of ASSRs is improved when the response is computed by averaging independent EEG epochs, containing only unadapted auditory responses. The improvements in the ASSR detection obtained with standard, weighted and sorted averaging were compared. In the absence of artifacts, when the ASSR was elicited by continuous acoustic stimulation, the computation of the ASSR amplitude relied upon the averaging method. While the adaptive behavior of the ASSR was still evident after the weighting of epochs, the sorted averaging resulted in under-estimations of the ASSR amplitude. In the absence of artifacts, the ASSR amplitudes computed by averaging independent epochs did not depend on the averaging procedure. Averaging independent epochs resulted in higher ASSR amplitudes and halved the number of EEG epochs needed to be acquired to achieve the maximum detection rate of the ASSR. Acquisition protocols based on averaging independent EEG epochs, in combination with appropriate averaging methods for artifact reduction might contribute to develop more accurate hearing assessments based on ASSRs.

Estimating multiple latencies in the auditory system from auditory steady-state responses on a single EEG channel

“…The accuracy of the extracted phases of the frequency components is important for estimating latency. Previous studies often average the EEG signals across a number of trials to reduce the background noise, so that ASSRs have a higher SNR 37 . Here, we employed two different methods, ‘AVG EEG’ and ‘AVG phase’ to extract the phase of a target frequency.…”

A High-Resolution LED Stimulator for Steady-State Visual Stimulation: Customizable, Affordable, and Open Source

“…A threshold SNR is defined to determine if the steady-state response is elicited. Alternatively, the steady-state response and mean RNL are statistically compared using Hotelling’s T2 multivariate test, which considers both the amplitude and phase of the oscillation [ 38 , 39 , 40 , 41 ].…”

“…Evidence suggests that changes in the amplitude of the SSVEP cannot be systematically observed when stimulus differences are limited to 500 milliseconds. Studies of the adaptation of steady-state responses conducted in other sensory modalities [ 38 , 39 ] illustrate that while the steady-state response adapts to long-lasting continuous stimulation [ 38 ], adaptation is negligible when using intermittent, repetitive stimulation [ 39 ], as employed in the acquisition of the SSVEP (stimulus of 3–5 s in length, with an inter-stimulus interval of approximately the same duration).…”

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

“…The EEG epoch of interest will hence follow: The stimulus complex consisted of a superposition of four cosine pure tones, at 461, 500, 504 and 537 Hz, starting at t=0 with initial phase 0. Here, the six distortion frequencies (i.e., the 2 nd order system products) in the top panel at [4,33,37,39,43,76] Hz, are shown and time-scaled by a factor 0.1, for illustrative purposes. Note that all six distortions also start with zero phase at t=0 (because of the good property of cosine; see Appendix C in Supplemental Material).…”