Experimental investigations of auditory externalization and the application of head-movement information to hearing-aid signal processing

Head movements have been shown to be crucial to the perception of internalization and externalization. Head-movement information can also provide improvements to hearing-aid signal processing. Instantaneous head-motion information measured from a head-mounted gyroscope has been utilized to control the directionality of hearing-aid microphone arrays, based on user behaviour and assumed listening intent. Simulations show gain improvements over fixed and adaptive arrays during head turns in specific listener-source configurations. Tests show improved localization ability over simulated fixed arrays for the majority of listeners. The head-mounted gyroscope output was used to compensate for head movements during estimates of source direction of arrival (DOA). Estimates of DOA for sound sources were compensated for head movement detected by the gyroscope. This resulted in improved DOA estimates during head movements in comparison to the same system without head movement compensation. An improved head-motion detection system (combined gyroscope, accelerometer and magnetometer) was used to resolve sources into the front or rear hemifield biomimetically. Estimates of source DOA were shifted clockwise or anti-clockwise with head movement and aggregated in two DOA estimate histograms. The histogram with the largest peak robustly determined the hemifield in which the source was located. The acoustic scene has also been stabilized during head movements, resulting in increased timescales for direction of arrival (DOA) estimates to be aggregated and hence more robust DOA detection during head movements. The limits of DOA estimation using two microphones have been extended from a single front or rear hemifield to 360À using head movements biomimetically to resolve front-back confusions by comparing differentially rotated histogramsAn externalized sound is one that is perceived outside the head, whereas an internalized sound is perceived inside the head. The effect of hearing aids on these phenomena was investigated through psychoacoustic experiments, a novel questionnaire and offline analyses. The importance of high-frequency pinna cues for externalization in normal-hearing and hearing-impaired listeners was investigated using open-ear simulations of different microphone placements, frequency responses, and the number of talkers. It was found that hearing-impaired listeners experienced a compressed or "flattened" perception of externalization in relation to pinna cues. The role of changes in the stimulus and source direction on the perception of externalization by hearing-impaired listeners with and without their hearing aids was also investigated. An effect of angle but no effect of hearing aids was found for hearing-impaired listeners. The effect of short-term acclimatization to hearing aids by normal-hearing listeners performing the same task was investigated; an effect of acclimatization was found. A questionnaire was developed to determine the prevalence of internalization in several situations. The prevalence of internalization increased with the number of hearing aids worn. The overall prevalence for any experience of internalization was 25% of the sample population. The effect of dynamic-range compression, signal type and listening environment on a potential indicator for internalization, the shape of the interaural-level-difference distribution, was analyzed. The analyses only indicated potential internalization under particular constraints related to listening environment and temporal resolution, not dynamic range compression.An externalized sound is one that is perceived outside the head, whereas an internalized sound is perceived inside the head. The effect of hearing aids on these phenomena was investigated through psychoacoustic experiments, a novel questionnaire and offline analyses. The importance of high-frequency pinna cues for externalization in normal-hearing and hearing-impaired listeners was investigated using open-ear simulations of different microphone placements, frequency responses, and the number of talkers. It was found that hearing-impaired listeners experienced a compressed or "flattened" perception of externalization in relation to pinna cues. The role of changes in the stimulus and source direction on the perception of externalization by hearing-impaired listeners with and without their hearing aids was also investigated. An effect of angle but no effect of hearing aids was found for hearing-impaired listeners. The effect of short-term acclimatization to hearing aids by normal-hearing listeners performing the same task was investigated; an effect of acclimatization was found. A questionnaire was developed to determine the prevalence of internalization in several situations. The prevalence of internalization increased with the number of hearing aids worn. The overall prevalence for any experience of internalization was 25% of the sample population. The effect of dynamic-range compression, signal type and listening environment on a potential indicator for internalization, the shape of the interaural-level-difference distribution, was analyzed. The analyses only indicated potential internalization under particular constraints related to listening environment and temporal resolution, not dynamic range compression