Abstract
The auditory steady-state response (ASSR) is one of the main approaches in clinic for health screening and frequency-specific hearing assessment. However, its generation mechanism is still of much controversy. In the present study, the linear superposition hypothesis for the generation of ASSRs was investigated by comparing the relationships between the classical 40 Hz ASSR and three synthetic ASSRs obtained from three different templates for transient auditory evoked potential (AEP). These three AEPs are the traditional AEP at 5 Hz and two 40 Hz AEPs derived from two deconvolution algorithms using stimulus sequences, i.e., continuous loop averaging deconvolution (CLAD) and multi-rate steady-state average deconvolution (MSAD). CLAD requires irregular inter-stimulus intervals (ISIs) in the sequence while MSAD uses the same ISIs but evenly-spaced stimulus sequences which mimics the classical 40 Hz ASSR. It has been reported that these reconstructed templates show similar patterns but significant difference in morphology and distinct frequency characteristics in synthetic ASSRs. The prediction accuracies of ASSR using these templates show significant differences (p < 0.05) in 45.95, 36.28, and 10.84% of total time points within four cycles of ASSR for the traditional, CLAD, and MSAD templates, respectively, as compared with the classical 40 Hz ASSR, and the ASSR synthesized from the MSAD transient AEP suggests the best similarity. And such a similarity is also demonstrated at individuals only in MSAD showing no statistically significant difference (Hotelling's T2 test, T2 = 6.96, F = 0.80, p = 0.592) as compared with the classical 40 Hz ASSR. The present results indicate that both stimulation rate and sequencing factor (ISI variation) affect transient AEP reconstructions from steady-state stimulation protocols. Furthermore, both auditory brainstem response (ABR) and middle latency response (MLR) are observed in contributing to the composition of ASSR but with variable weights in three templates. The significantly improved prediction accuracy of ASSR achieved by MSAD strongly supports the linear superposition mechanism of ASSR if an accurate template of transient AEPs can be reconstructed. The capacity in obtaining both ASSR and its underlying transient components accurately and simultaneously has the potential to contribute significantly to diagnosis of patients with neuropsychiatric disorders.
Highlights
The auditory steady-state response (ASSR) elicited by periodical auditory stimulation is a major approach in clinic for hearing screening and frequency-specific hearing assessment (e.g., Silva et al, 2013; Francois et al, 2016)
The major middle latency response (MLR) components follow tightly, such as Pa occurring at ∼25 ms, behind the early response components usually termed as auditory brainstem responses (ABRs) (Galambos et al, 1981; Stapells et al, 1984)
The theory describes that ASSR is the linear mixing of multiple underlying transient auditory evoked potential (AEP) each evoked by a stimulus periodically presented in a sequence
Summary
The auditory steady-state response (ASSR) elicited by periodical auditory stimulation is a major approach in clinic for hearing screening and frequency-specific hearing assessment (e.g., Silva et al, 2013; Francois et al, 2016). ASSRs, recorded from the human scalp, have been found remarkably pronounced at 40 Hz as compared with other stimulus rates (Picton et al, 2003) Such an enhancement can be explained by the in-phase superimposition of a sequence of transient auditory evoked potentials (AEPs) elicited by individual stimuli. The major middle latency response (MLR) components follow tightly, such as Pa occurring at ∼25 ms, behind the early response components usually termed as auditory brainstem responses (ABRs) (Galambos et al, 1981; Stapells et al, 1984) Proximity of these components and matching time intervals (25 ms equal to time interval among individual stimuli at 40 Hz stimulus rate) strongly support the linear superposition theory accounting for the generation mechanism of ASSR. Based on the theory, if assuming each transient AEP is same, it can be used as a template for the transient response of each stimulus to reconstruct ASSR, together with the timing of individual stimuli in the stimulus sequence
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