Level-Dependent Hearing Protectors Can Switch the Perception of Sound Direction in a Hazardous Way

Level-dependent hearing protectors enable to perceive soft- to medium-level sounds without processing, while protecting the ear against hazardous high-level signals by active level attenuation. However, the level-dependent behavior can potentially affect naturally occurring binaural cues and, hence, impair localization abilities. This study therefore investigated the influence of two hearing protectors (earplug and earmuff), each in passive and one active setting, on localization of reverse alarms in noise at two signal levels compared to open ears. Localization was measured in 16 normal-hearing subjects inside a horizontal array of 48 loudspeakers. Additionally, the stimuli were recorded with an artificial head in the same measurement setup to investigate the corresponding interaural cues. The results showed that especially the active earmuff at the higher level led to a reversed perception of the target direction. The objective measurements revealed large changes of interaural level differences with earmuffs compared to open ears which were mostly consistent with the subjects’ responses. These findings indicate that it is critical to test electronic hearing protectors with respect to changes in interaural cues to avoid safety risks due to impeded localization. Results also indicate that measured interaural cues can provide an estimate of the perceived sound direction by human listeners.