William S. Woods
Andrew R. Brughera
H. Steven Colburn
Dept. of Biomed. Eng., Boston Univ., 44 Cummington St., Boston, MA 02215
The work reported here investigated whether across-frequency comparisons can be made when the only relevant information is contained in binaural comparisons. Subjects were required to detect a difference in interaural correlation (IC) between a target band and surrounding fringe bands. Noise stimuli of 500-ms duration and 115-, 354-, 1000-, and 4000-Hz bandwidth, centered on 500 Hz, were used in an adaptive 2I,2AFC task. In each interval, the reference IC was roved between 0.7 and 1.0. In the target interval, the IC was additionally reduced in the 115-Hz target band centered on 500 Hz. Results indicate that the threshold reduction-in-IC is lowest for the 115- and 4000-Hz bandwidth conditions, and highest for the 354-Hz bandwidth condition, consistent with subjects' use of across-frequency comparisons of binaural information. For the 1000- and 4000-Hz conditions, subjects reported using the presence of a perceived narrow-band object in the target interval as the basis for decision. This basis was eliminated by delaying the onset of the 115-Hz target band 500 ms relative to the fringe band. Resulting thresholds were unchanged or smaller than in the corresponding synchronous condition, possibly due to the subjects' use of image-width cues.