Temporal pitch perception and the binaural system

Two experiments examined the relationship between temporal pitch (and, more generally, rate) perception and auditory lateralization. Both used dichotic pulse trains that were filtered into the same high (3,900-5,400-Hz) frequency region in order to eliminate place-of-excitation cues. In experiment 1, a 1-s periodic pulse train of rate Fr was presented to one ear, and a pulse train of rate 2Fr was presented to the other. In the "synchronous" condition, every other pulse in the 2Fr train was simultaneous with a pulse in the opposite ear. In each trial, subjects concentrated on one of the two binaural images produced by this mixture: they matched its perceived location by adjusting the interaural level difference (ILD) of a bandpass noise, and its rate/pitch was then matched by adjusting the rate of a regular pulse train. The results showed that at low Fr (e.g., 2 Hz), subjects heard two pulse trains of rate Fr, one in the "higher rate" ear, and one in the middle of the head. At higher Fr (>25 Hz) subjects heard two pulse trains on opposite sides of the midline, with the image on the higher rate side having a higher pitch than that on the "lower rate" side. The results were compared to those in a control condition, in which the pulses in the two ears were asynchronous. This comparison revealed a duplex region at Fr > 25 Hz, where across-ear synchrony still affected the perceived locations of the pulse trains, but did not affect their pitches. Experiment 2 used a 1.4-s 200-Hz dichotic pulse train, whose first 0.7 s contained a constant interaural time difference (ITD), after which the sign of the ITD alternated between subsequent pulses. Subjects matched the location and then the pitch of the "new" sound that started halfway through the pulse train. The matched location became more lateralized with increasing ITD, but subjects always matched a pitch near 200 Hz, even though the rate of pulses sharing the new ITD was only 100 Hz. It is concluded from both experiments that temporal pitch perception is not driven by the output of binaural mechanisms.