Localization accuracy of phantom sound sources on the horizontal plane by bilateral hearing aid users in aided free-field and non–free-field conditions

This study investigates the use of amplitude panning in a localization accuracy test and the influence of a non-ideal environment on its feasibility as a clinical tool. The horizontal localization accuracy of 16 normal-hearing participants and ten bilateral hearing aid users was assessed for real and amplitude panned sound sources produced over loudspeakers. Localization accuracy was measured with speech-shaped noise in both an anechoic chamber (free-field) and an acoustically treated listening room (non-free-field). The root mean square error between the response angle and the target angle was calculated for each participant. Thus, the root mean square error for the two sound source types for each test environment could be calculated and compared, and also contrasted against existing literature. Statistical analysis of the control group results revealed an effect of the target angle, method used (real vs amplitude panning) and environment (free-field vs non-free-field). An interaction between target angle and environment was also found. For the hearing aid user group, however, only an effect of target angle was found, which may lend support to simpler setups with fewer loudspeakers in non-free-field environments. However, the effect of the room varied between individuals within this group, thereby warranting further exploration.