The Effect of Head Movements on Front-Back Discrimination and Sound Externalization With Hearing Aids

Head movements are intuitive, often spontaneous, behaviours that help us localize the origin of a sound source. In normal-hearing listeners, head movements during sound presentation are known to improve localization performance in both horizontal and vertical dimensions, as well as front-back discrimination. The perceived externalization of sound sources also improves with head motion. Hearing-aid users, especially users with behind-the-ear microphone positioning, exhibit diminished front-back localization abilities as well as degraded externalization under static conditions. The extent to which active head movements can overcome the spatial degradations introduced by hearing aids remains unclear. The current study aimed to provide quantitative data on this issue. Participants with normal hearing were fitted with low-gain hearing aids and presented with speech stimuli from a loudspeaker directly in front or behind. They performed front-back discrimination, rated perceived externalization, and did so with or without head movements. We hypothesized that head movements would fully resolve front-back confusions and restore externalization ratings to unaided levels. Instead, head movements were more effective in resolving front-back confusions than externalization breakdowns. We conclude that hearing-aid related spatial distortions may not be fully overcome by active head movements and note large inter-individual differences in the relationship between externalization and front-back discrimination.