Experiments were performed on the discrimination of interaural time for lateralization images on the midline, using filtered 10 microsec. duration pulse with repetition rate 100 PPS as stimulus sound. Employing simplified AB method, interaural time DLs (ITDL) were investigated as a function of sensation level of stimuli, cut-off frequency of presentation filter (hi-pass, low-pass, and band pass), and aging of subjects.
1) ITDLs in 0. 7 and 2 kHz (fo) half octave bands decreased rapidly until the stimulus level reached to 40 dB SL, beyond which they were approximately constant.
2) When half octave band filters were used at 50 dB SL presentation level, ITDLs gave approximately same value in 0. 5, 0. 7 and 1 kHz bands, but they rapidly increased in 2 and 4. 6kHz bands.
Employing wider frequency band filtering, ranging from 1/2 to 3 1/2 octaves, every of which contained 0.7 kHz 1/2 octave band, it was found that cutting off higher frequency rather than lower frequency seemed to improve ITDL. ITDL curves cut-off frequency of high pass and low pass filters crossed at around 800 Hz.
These findings suggest that the frequency range of 0.7 kHz in terms of 1/2 octave band plays an important role in sound lateralization.
3) ITDLs in 0.7 kHz 1/2 octave band at 50 dB SL were measgred in 54 subjects including every decade of age. Average ITDL increased with advance of age, being the smallest ITDL(28 microsec.) in twenties and the largest in sixties or more
