William S. Woods
Univ. Oldenburg, FB8/Medizinische Physik, D-26111 Oldenburg, Germany
The discrimination of the ITD of a 600-Hz tone was measured in the presence of other tones, with levels of 75 and 45 dB SPL/tone, spacings of 200 and 400 Hz, and in the presence of noisebands. Noiseband levels were such that excitation patterns with tonal and noise interferers were equal in a region around the target. Tonal interferers were presented with simultaneous onsets and offsets, 250-ms onset asynchrony, or continuously. Noisebands were presented continuously. At the lowest presentation level with the widest spacing and continuous tonal interferers, jnds showed no increase over the target-alone jnd, i.e., no interference. Decreased spacing or increased level caused increased jnds (i.e., interference). Lesser-experienced subjects showed more interference in the asynchronous-onset condition than in the continuous-tone condition. Measurements of intensity jnds in a subset of conditions yielded similar results. These results are consistent with interference caused by spread of excitation and pulsing of interferers being as significant as interference expected from auditory grouping. A filter-based cross-correlation model for ITD processing is shown to be consistent with past and present ITD jnd results. [Work supported by NIDCD (Grant DC00100).]