THE EFFECT OF DISTRACTOR FREQUENCY ON JUDGMENTS OF TARGET LATERALITY BASED ON INTERAURAL DELAYS

A two-dimensional stimulus-classification paradigm was used to examine the ability of listeners to judge the laterality of an interaurally d elayed low-frequency target component presented concurrently with a di stracter component. Of primary interest was the effect on performance of the frequency difference (Delta f) between the target and distracte r. In one set of conditions, the target was fixed at 753 Hz and the di stracter was 353, 553, 653, 703, 803, 853, 953, or 1153 Hz (fixed with in a block of trials). In a second set of conditions, the distracter w as fixed at 753 Hz and the target frequency was 353, 553, 653, 703, 80 3, 853, 953, or 1153 Hz. The listeners were presented with a target co mponent with an interaural delay that varied from trial to trial, taki ng on one of ten values, five leading to the left ear and five leading to the right. A distracter component was simultaneously presented wit h an interaural delay that also took on one of the same ten values. De lays ranged from -90 to +90 mu s in 20-mu s steps. During a block of 1 00 trials, each of the possible combinations of target and distracter delay was presented once and only once in a random order. Listeners we re instructed to make left-right judgments based on the target delay. Each condition was repeated ten times, and the slopes of the best line ar boundaries between left and right responses were used to derive the relative weights given to the target and distracter. The duration of the signals was 200 ms. Two of the eight listeners weighted the target heavily when the target and distracter were spectrally remote but gav e the two components equal weight when the difference in frequency was small. These two listeners yielded similar target weights regardless of which component was designated as the target. One listener gave nea rly equal weight to the target and the distracter regardless of Delta f. Five of the listeners gave greater weight to the higher of the two frequencies regardless of which was assigned as the target. This high- frequency dominance is explained in terms of cross-correlation functio ns based on the composite two-tone waveforms. (C) 1996 Acoustical Soci ety of America.