Spatial auditory masking between sound objects positioned vertically on the listener’s median and sagittal planes has been investigated. Previous studies showed that the masking threshold exhibits symmetry with respect to the frontal plane of the listener—meaning that signals at the front center mask signals at the back center just as effectively as those at the front. In this study, we confirmed that not only signals at the front center but also those at various elevations along the median plane can mask other signals at different elevations on the same plane, regardless of their specific elevation. In other words, the masking threshold remains nearly constant, independent of the elevations of both the masker and the maskee, as long as they lie on the median plane or the same sagittal plane. This was confirmed using masker signals not only near 400 Hz but also near 1 kHz, which is also an important frequency band for human hearing. These results support the hypothesis that differences in interaural time differences (ITDs) between the masker and maskee signals influence the masking threshold.
Araseki et al. (2025) studied this question.