EXPRESS: Investigating Amplitude Envelope’s Role in Auditory Alarm Masking

Auditory alarms conveying hospital patient information face extensive criticism regarding their effectiveness. Previous research indicates that changing the amplitude envelope of alarms from temporally invariant flat to decaying percussive improves detectability and lowers annoyance. Here we complement and extend this research by exploring masking - when simultaneous signals obscure one another. The experiment consists of a three-alternative forced choice task in which participants decide which of 3 presented white-noise 'masker' tones contain a target tone. We manipulated masker amplitude envelope and the target timing (relative to the masker) within-subjects. We determined masking thresholds (the volume at which the masker completely obscures the target through a 2-down 1-up adaptive staircase. We find percussive maskers produce substantially lower thresholds than flat maskers, regardless of target timing. These may reflect (1) the asymmetrical energy distribution of percussive sounds creating opportunities for detecting overlapping alarms, and (2) a reduction in synaptic inhibition for percussive relative to flat sounds. This offers foundational evidence in favour of percussive envelopes reducing alarm tone masking - findings with implications both for our theoretical understanding of masking, and as potential direct application in auditory alarms.