Binaural processing of filtered transients

Binaural processing of transient stimuli plays an important role in our ability to localize sound in reverberant environments. We were interested in determining the spectral region in which binaural processing of transients takes place. The experiments examined thresholds for reporting two clicks, detecting interaural time differences, and detecting clicks masked binaurally, as a function of four filtering conditions: low-pass filtering at 10,000 Hz and band-pass filtering between 125-500, 500-2000, and 2000-8000 Hz. As the center frequency of the filters increased, the interaural two-click thresholds decreased from approximately 3.2 to 1.0 msec and the interaural time difference thresholds increased from approximately 20 to 90 μsec. Masking level differences (MLDs) were computed for masked clicks presented with an interaural time delay, with an interaural phrase reversal, or to only one ear; noise was presented the same to both ears. The MLDs were maximal when the clicks were presented with interaural delays of 1.0 to 2.2 msec and with interaural phase reversal, under all filtering conditions except for 2000-8000 Hz, in which the MLD was never greater than 2 db. With an interaural delay of approximately 15 msec, MLDs for the interaural delay conditions were within 1 db of MLDs obtained in the one-ear condition. The data indicate that all three procedures reflect the same aspects of binaural processing and that binaural processing of acoustic transients is due primarily to energy at low frequencies.