Sound localization. The interaction of aging, hearing loss and hearing protection.

The effect of conventional ear plugs and ear muffs, and muffs with limited dichotic amplification on the ability to localize one-third octave noise bands was investigated under semi-reverberant listening conditions. Forty-eight normal-hearing subjects, half over 40 years of age, and 23 subjects with bilateral sensorineural hearing loss participated. Sound localization was assessed using an array of six loudspeakers surrounding the subject at azimuth angles 60 degrees apart. One block of 120 forced-choice speaker identification trials was presented for each of 16 listening conditions defined by ear condition (unoccluded, E-A-R plug, E-A-R muff, and Bilsom 2392 muff), stimulus frequency (500 Hz and 4000 Hz), and background (quiet and continuous 65 dB SPL-white noise). Plugs and muffs, particularly active muffs, resulted in decrements in right/left judgments based on interaural intensity but not time-of-arrival differences. High-frequency front/back discrimination was affected more by muffs than by plugs. Error patterns for the conventional and active muffs were dissimilar. Aging resulted in a decrement in unoccluded front/back discrimination. Trends for the impaired subjects were the same as those for normal subjects at 500 Hz. Many could not hear 4000 Hz with conventional protectors. Their performance was no different from normal with the active muffs.