Sound source identification with ANR earmuffs

The effect of hearing protective earmuffs which incorporate active noise reduction (ANR) on sound source identification was studied. The purpose was determine whether ANR interfered with the encoding of cues normally used for directional hearing. Right/left, front/back and within quadrant confusions were assessed in quiet using a circular array of eight loudspeakers. Three stimuli, one-third octave bands centred at 0.5 kHz and 4 kHz and broadband noise, were presented. These enabled an assessment of the utilization of mainly interaural time-of-arrival and level differences, and binaural and spectral cues in combination, respectively. Two groups of normal hearing subjects aged 18-30 and 40-55 years, half male and half female, participated. Overall, age, gender, and ANR were not significant determinants of outcome. The probably of correctly discriminating among the eight speakers decreased significantly with the muffs worn, relative to unoccluded listening by 10%, 35% and 40% for the 0.5 kHz, 4 kHz and broadband stimuli, respectively. The pattern of errors indicated that the earmuffs interfered with the encoding of both binaural (interaural level differences) and spectral cues. With ANR small additional right/left confusions were observed for the low-frequency stimulus (time-of arrival cue) for speakers close to the midline axis. The results provide further evidence that earmuffs should not be used in situations where the perception of the direction of hazard is a concern. ANR technology does not appear to increase the handicap.