The authors used magnetoencephalography (MEG) to assess how spatial novelty affects transient auditory evoked fields and the 40-Hz auditory steady-state response (ASSR). Recordings were obtained from 23 healthy participants while they listened to binaural auditory stimuli presented at 40 Hz. Stimuli were lateralized to the left or right using interaural time differences and presented in a pseudo-random sequence.
Binaural stimuli at 40 Hz were delivered such that each trial was perceived as lateralized to one side by manipulating interaural timing. The pseudo-random presentation allowed the authors to create conditions in which a given stimulus either followed a stimulus on the same side or followed one on the opposite side, enabling explicit comparison of responses to spatially novel versus repeated-side stimuli.
Trials were classified by whether the preceding stimulus had been presented on the same side or on a different side. The authors further stratified trials based on the number of consecutive preceding stimuli that had been on the different side, permitting assessment of graded novelty effects. Outcome measures included amplitude of transient auditory evoked components (notably the N100m) and metrics of the 40-Hz ASSR such as spectral power and phase synchronization.
Spatial novelty consistently modulated the transient auditory evoked response indexed by the N100m. Specifically, N100m amplitudes were larger following a stimulus that appeared on a different side compared with when the preceding stimulus had been on the same side. Moreover, the N100m exhibited a graded increase in amplitude as the number of preceding different-side stimuli increased, indicating sensitivity of this transient evoked component to the recent spatial history of stimulation.
In contrast to the N100m, the 40-Hz ASSR showed no measurable modulation by spatial novelty in this study. Both ASSR power and phase synchronization remained unchanged by whether the current stimulus followed a same-side or different-side stimulus, and they did not display the graded response seen in the N100m with increasing numbers of preceding different-side stimuli.
The dissociation between novelty effects on the N100m and the lack of effect on the 40-Hz ASSR suggests that novelty sensitivity of gamma-band steady-state oscillations depends on the stimulus dimension that changes. Prior work had indicated that novelty tied to temporal and physical stimulus features can modulate the 40-Hz ASSR; however, spatial novelty produced by interaural time differences in this paradigm did not alter ASSR magnitude or synchronization.
These results imply that novelty-related activity captured by transient evoked fields (for example, N100m) does not necessarily have a direct counterpart in steady-state gamma-band responses. Therefore, the 40-Hz ASSR may not serve as a universal proxy for novelty detection across all stimulus dimensions. The authors frame this outcome in the context of seeking reliable biomarkers—particularly those based on gamma-band activity—for psychiatric or neurological conditions: sensitivity of ASSR measures to novelty may be conditional on how novelty is defined and implemented.
The abstract and article summary report the principal experimental design and group-level outcomes but do not provide detailed methodological parameters in this summary (for example, exact stimulus timing values, preprocessing steps, or statistical thresholds). The study used healthy adult participants; any extension to clinical populations or younger age groups would require further investigation. The authors also note prior evidence that other novelty types can influence the 40-Hz ASSR, indicating that the relationship between novelty and ASSR may be stimulus-dimension dependent.
In 23 healthy adults, spatial novelty produced by interaural time differences enhanced the amplitude of the N100m in a graded fashion but did not affect the 40-Hz ASSR in terms of power or phase synchronization. The findings support a dissociation between transient auditory evoked fields and gamma-band steady-state responses in their sensitivity to spatial novelty. Clinically, this suggests caution when interpreting 40-Hz ASSR measures as general indices of novelty detection: their sensitivity may be limited to particular types of stimulus change and may not parallel evoked-field markers like the N100m.
Conflict of interest
The authors declared no known competing financial interests or personal relationships that could have influenced the reported work.
Keywords
Auditory evoked field; 40-Hz ASSR; interaural time difference; magnetoencephalography; neural oscillation; novelty detection.
References and publication details
This study appears as a free article in Neuroscience (2026), PMID 42229828, DOI 10.1016/j.neuroscience.2026.05.042. The abstract and article metadata are the source of the summarized facts above.