Earmuffs, exploratory head movements, and horizontal and vertical sound localization

In a semi-anechoic room, normal-hearing adults judged the position of that loudspeaker emitting a narrow-band noise centered at 1 kc/s, from a vertical array of 10 loudspeakers in 18 degrees steps, or a similar horizontal-arc array intersecting at 0 degrees azimuth and 0 degrees vertical. Stimuli were narrow-band noise bursts terminated by S when judgment was made. Ss (N:17) were free to move their heads, or were asked to restrict such movement. In the horizontal plane, Ss without earmuffs and with free head movement performed with 95% absolute accuracy but, with earmuffs, accuracy fell off to 50%, and when head movements were restricted accuracy fell off further to 24%. The results of Fisher and Freeman (J. Aud. Res., 1968, 8, 15-26) were generally confirmed, but free head movements did not, as in their study, totally "wash out" functional pinna removal. In the vertical plane, Ss with earmuffs even with free head movements yielded only 19% absolute accuracy, though without earmuffs accuracy rose to 72%. A postulate arising from this study is that listeners are unable to recruit remaining (interaural) cues when these are generated under different bodily orientations. The potential practical hazard suggested by the results is noted.