Bone-conducted sound lateralization of interaural time difference and interaural intensity difference in children and a young adult with bilateral microtia and atresia of the ears

Bone-conducted sound lateralization tests to determine interaural time difference (ITD) and interaural intensity difference (IID) were conducted by means of a self-recording apparatus in 20 children and a young adult with bilateral microtia and atresia of the ear. This apparatus changes ITD automatically from 0 to 2,000 micros at 50 micros/s and IID from 1 to 40 dB at 1 dB's. When ITD exceeds approximately 200 micros/s and IID exceeds 5 dB in normal subjects the sounds are recognized separately. The test stimulus was a continuous narrow-band noise at 500 Hz and 30 dB SL applied to the right and left mastoids through bone vibrators. In the patients with bilateral atresia of the ears, ITD results revealed approximately normal thresholds of discrimination in half the patients and IID results revealed threshold elevation in only 10%. It is noted that bone-conducted sound lateralization abilities of ITD or IID are maintained in many of these patients.