Effectiveness of changing stimulus frequency and intensity of sound for evaluating hearing by monitoring pupil responses

Assessing hearing through the pupil dilation response (PDR) to sound offers a non-invasive alternative to traditional audiometry, particularly useful in individuals unable to provide behavioral responses. However, reliable detection of sound-evoked PDRs is limited by variability in pupil size and the risk of false positives (Type I Errors). This study investigated whether pseudo-random variation of sound frequency and amplitude enhances the correspondence between PDR detection and sound perception in normal-hearing subjects. To improve reliability, epochs with different pre-stimulus pupil sizes were analyzed separately, as baseline pupil diameter affects PDR amplitude. Pupil responses to auditory stimuli were recorded, averaged, and compared with baseline data obtained in silence. Additional averages were computed for specific frequencies, amplitudes, and pre-stimulus pupil size ranges. Sub-threshold PDR traces were further processed by averaging all possible differences between sound and baseline frames. The probability of Type I Errors was estimated using randomly sampled baseline data. Results show that using stimuli with varying frequency and amplitude markedly increased PDR retrieval compared with standard constant-tone paradigms. Restricting analysis to defined pre-stimulus pupil size ranges or specific stimulus parameters further improved detection rates. The difference-averaging method confirmed several low-amplitude PDRs as genuine responses, though some may still occur by chance. Overall, significant PDRs were observed in 80% of participants, indicating that while this approach enhances sensitivity, further refinement is needed before clinical application. More efficient paradigms are required to establish reliable, objective hearing assessment “by looking into the eyes.”