Impacts of ITD-based training on auditory-spatial illusion with aging: a combined MMN and behavioral study

Abstract Background The Franssen illusion (FE) is an auditory spatial illusion whose mechanisms are not fully understood. According to the Plausibility Hypothesis, the FE arises from abnormal Interaural Time Difference (ITD) cues. This study investigated the effects of ITD-based spatial hearing training and aging on FE occurrence, using both behavioral and Mismatch Negativity (MMN) measures. Method Fifty participants were included: 24 older adults (≥ 60 years; mean age 68.42 ± 1.38 years; 54.2% male) and 26 young adults (19–28 years; mean age 21.69 ± 0.42 years; 30.8% male). Behavioral experiments and oddball paradigms assessed FE occurrence and ITD scores across age groups. Among older adults, 19 underwent ITD-based training, with pre- and post-training assessments. Results A three-way mixed ANOVA revealed a significant reduction in ITD errors following training ( p = 0.002). However, training did not significantly influence FE occurrence ( p > 0.3). A significant age effect was observed, with younger participants experiencing fewer FE occurrences than older participants ( p < 0.001). Conclusion Combining behavioral and MMN measures, this study demonstrates that younger adults experienced the illusion less frequently than older individuals, likely due to age-related challenges in processing sounds in reverberant environments. Although ITD-based training enhanced binaural temporal resolution, it did not affect FE occurrence, suggesting that the illusion is not determined solely by ITD cues and that the training may have influenced both transient and sustained stimulus components equally.