PP503 - Comparison of 90Hz and 40Hz New-Generation ASSR Thresholds to Behavioral Thresholds

Abstract:
This study examined the relationship between new-generation multiple ASSR thresholds obtained using 90Hz and 40Hz protocol across frequencies and compared them to behavioral thresholds in normal-hearing adults. The preliminary analysis indicated that the 40Hz ASSR exhibited lower thresholds compared to 90Hz ASSR at 500Hz and 1000Hz and the 40 Hz ASSR protocol resulted in a lower difference when compared to behavioral thresholds over the 90Hz protocol, particularly at 500Hz and 1000Hz frequencies. The study highlights a need for a large-scale study to measure the effectiveness 40Hz protocol in assessing infants.

Summary:

Background:
The auditory steady-state response (ASSR) is a sustained phase-locked electrophysiological response evoked by a repetitive stimulus. ASSR provides a quick, accurate, and objective estimation of behavioral hearing thresholds. The new generation ASSR, which uses NB-CE Chirp stimuli, has demonstrated superior amplitude, shorter testing time, consistency across tested frequencies, resistance to sleep-state interference, and a reduced mean difference when compared to behavioral thresholds (Mühler et al., 2012; Mühler et al., 2014; Maeda et al., 2017; Sininger et al., 2018; Dabbous et al., 2017; Christensen et al., 2022). There is a gap in the literature regarding comparing 40Hz and 90Hz new-generation ASSR protocols with behavioral thresholds. Although Kinoshita et al. (2021) conducted a study in Japan comparing the two, no manuscript is available in English. This study will evaluate the relationship between new-generation ASSR thresholds obtained with 40 Hz and 90 Hz protocols and compare them to behavioral thresholds. We hypothesized that the 40Hz and 90Hz ASSR thresholds would strongly correlate with behavioral thresholds.

Methods:
The study recruited normal-hearing participants from the Department of Communication Disorders, California State University, and the local population. A two-channel recording montage was utilized. The non-inverting electrode was placed at the forehead at the hairline, two inverting electrodes were placed on each mastoid, and the ground electrode was placed on the mid-forehead. ASSR recordings were completed while the subject relaxed or, in most cases, slept on a recliner. Multiple-Stimuli ASSR were recorded for 40Hz and 90Hz protocols via insert earphones. ASSR thresholds were determined using the modified Michel and Jorgensen (2017) procedure. Behavioral thresholds were obtained through a modified Hughson and Westlake procedure and were then compared with ASSR thresholds obtained using the 40Hz and 90Hz protocols.

Results:
The preliminary analysis indicates that the 40Hz ASSR exhibited lower thresholds than 90Hz ASSR at 500Hz and 1000Hz, averaging 15 dB and 10 dB lower, respectively. However, at 2000Hz and 4000Hz, the 40Hz and 90Hz ASSR protocols displayed comparable thresholds. The difference between ASSR and behavioral thresholds is reduced for 40Hz compared to 90Hz ASSR protocols at 500Hz and 1000Hz, but similar results were obtained for 2000Hz and 4000Hz. In summary, these findings suggest the superiority of the 40Hz ASSR protocol over the 90Hz protocol, particularly at 500Hz and 1000Hz frequencies.

Conclusions:
This study affirms the stability and precision of the new-generation 40Hz ASSR protocol, mainly when applied in an asleep protocol. The 40 Hz ASSR thresholds closely align with behavioral thresholds, maintaining consistency within a 5dB range across 500Hz to 4000Hz. These robust outcomes stem from generating larger amplitude responses using the 40Hz protocol. These findings advocate for incorporating a dedicated 40Hz protocol or a hybrid strategy, incorporating 40Hz for lower frequencies and 90Hz for higher frequencies in clinical assessments. Additionally, these research results highlight the urgent need for a comprehensive large-scale assessment to gauge the effectiveness of the new-generation 40Hz protocol in assessing infants' ASSR.