Upper/lower asymmetricity and inter-individual variability in summing localization in the median plane

Previous studies reported that, when two identical sounds are presented from different directions in the median plane, the sound image perception differs from that in the horizontal plane. The current study performed a psychoacoustical experiment to explore the summing localization occurring in the median plane. The results coincide with the literature, showing weaker summing localization in the median plane than in the horizontal plane. Furthermore, the results indicate an upper-lower asymmetricity and inter-individual variability in the summing localization in the median plane. These results also hold for the case without time delay between the two sounds, namely, the amplitude panning.