Probing Spectral Masking With Auditory Steady-State Responses

Behavioral measurements of auditory masking have been fundamental in developing models of hearing. However, their clinical utility-their feasibility and usefulness in routine patient assessment-is limited because they are attention-dependent and rely on active participation. Moreover, the behavioral masking paradigm requires a large number of stimulus combinations (multiple masker and probe configurations) and can be time-consuming for participants compared to standard audiometry. Auditory steady-state responses (ASSRs) provide an objective alternative and are already widely used to estimate auditory thresholds in quiet. Unlike behavioral methods, ASSRs can be recorded from individuals who cannot provide reliable behavioral responses, such as infants or patients with cognitive or communication difficulties. However, the relationship between ASSRs and behavioral masking thresholds remains unclear. This study investigated how spectral masking affects ASSRs and how these effects relate to behavioral masking thresholds. We hypothesized that, when probes are presented at equal levels above individual behavioral masking thresholds, the resulting ASSR masking effect would remain constant, regardless of probe frequency or masker level.

This study examined masking effects on ASSRs in 25 normal-hearing adults. Behavioral masking thresholds were first obtained using a low-pass noise masker with a 707 Hz cutoff presented at 65 and 85 dB SPL. Probe signals were one-third-octave-wide noise centered at 891 and 1414 Hz. ASSRs were then recorded to 40-Hz amplitude-modulated probes presented at 20 and 30 dB above individual behavioral masking thresholds. ASSRs were recorded in both masker-present and masker-absent conditions, using scalp- and ear-EEG. ASSR amplitudes were compared across conditions using permutation tests and linear mixed-effects modeling.

ASSR amplitudes were consistently reduced in masker-present compared to masker-absent conditions, confirming that the presence of the masker affects electrophysiological responses. However, the magnitude of the masking effect varied with experimental parameters. At 65 dB SPL, ASSR amplitudes remained relatively stable across probe frequencies, whereas at 85 dB SPL, amplitudes at 1414 Hz were significantly lower than at 891 Hz across all recording configurations. Contrary to our hypothesis, equal probe levels relative to the behavioral masking thresholds did not yield constant masking effects. The data support a model in which electrophysiological responses integrate activity across multiple auditory filters, whereas behavioral detection is dominated by the internal filter with the highest signal to noise ratio.

ASSRs are systematically influenced by spectral masking, with effects depending on masker intensity, probe frequency, and presentation level. Results of the study demonstrate that ASSRs can be used to probe auditory masking and highlight ASSR's potential as an objective tool for assessing individual masking thresholds.