Interaural Correlation and Earphones
Jerry V. Tobias, Lloyd A. Jeffress · The Journal of the Acoustical Society of America · 1960
In a recent paper, J. V. Tobias and E. D. Schubert [J. Acoust. Soc. Am. 31, 1595–1605 (1959)] suggested an “effective onset-duration” of 1–3 msec which they related to the “on-effect” and to the minimum refractory period of fibers of the VIIIth nerve. In the present experiments, an attempt was made to measure the critical duration by playing pairs of binaural stimuli with interaural correlations of +1 and −1 (or −1 and +1) and determining the duration below which the two conditions could not be recognized as different. For both noise-burst and click stimuli through PDR-8 earphones, stimulus durations were varied down to 0.09 msec. Judgments were 100% correct for all conditions. Acoustic measurements showed that, although waveform varied with varying duration of electrical input, the acoustic period remained at least 1 msec long. Indeed, for a given short-duration (less than a millisecond or so) burst of electrical noise, the acoustical waveform was surprisingly constant. The same sort of experiment, done with a comparison of +1 and 0 (uncorrelated) stimuli, produced similar results. The basic finding, then, is that stimuli delivered via PDR-8's cannot be changed enough electrically to produce acoustically an “unsolvable” interaural-correlation problem. It is apparent that the binaural system can solve any duration-sensitive transform that is transduced through standard earphones. (This work was partially supported by the Bureau of Ships.)