Context dependence of fundamental-frequency discrimination: lateralized temporal fringes

In a two-interval, two-alternative, forced-choice: (2I-2AFC) adaptive proce dure, listeners discriminated between the fundamental frequencies:(F0s) Of two 100-ms harmonic target complexes. This ability can be impaired substant ially by the presence of another complex (the "fringe") immediately before and after each target complex. It has been shown that for the impairment to occur (i) target and fringes have to be in:the same frequency region; (ii) if all harmonics of target and fringes are unresolved then they may differ in F0; otherwise, they have to be. similar [C. Micheyl and R. P. Carlyon, J. Acoust. Sec. Am. 104, 3006-3018 (1998)]. These findings have been discus sed in terms of information about the fringe's F0 being included in the est imate of the F0 of the target, and in terms of auditory streaming. The pres ent study investigated the rule of perceived location and ipsilateral versu s contralateral presentation of the fringes on F0 discrimination of the tar get. Experiment 1 used interaural level differences (ILDs), and experiment 2 used interaural time differences (ITDs) to create a range of lateralized perceptions of the 200-ms harmonic fringes. Difference limens for the F0 of the monaural target complex were measured in the presence and absence of t he fringes. The nominal F0 was 88 or 250 Hz and could be the same or:differ ent for target and fringes. Stimuli were bandpass filtered between 125-625 , 1375-1875, or 3900-5400 Hz. In both experiments, the effect of the fringe s was reduced when their subjective location differed from that of the targ et. This reduction depended on the resolvability of both the fringes and th e target, The effect of the fringes was reduced most (but still present), w hen fringes were presented purely contralaterally to the target. The result s are consistent with the idea that the fringes produce interference when t he listeners have difficulty segregating the target from the i:fringes, and that a difference in perceived location enhances segregation of the sequen tially resented stimuli. (C) 1999 Acoustical Society of America. [S0001-496 6(99)05712-4].