Dual temporal pitch percepts from acoustic and electric amplitude-modulated pulse trains

Two experiments examined the perception of unmodulated and amplitude-modula ted pulse trains by normally hearing Listeners and cochlear implantees. Fou r normally hearing subjects listened to acoustic pulse trains, which were b and-pass filtered between 3.9 and 5.3 kHz. Four cochlear implantees, all po stlinguistically deaf users of the Mini System 22 implant, listened to curr ent pulse trains produced at a single electrode position. In the first expe riment, a set of nine loudness-balanced unmodulated stimuli with rates betw een 60 and 300 Hz were presented in a multidimensional scaling task. The re sultant stimulus spaces for both subject groups showed a single dimension a ssociated with the rate of the stimuli. In the second experiment, a set of ten loudness-balanced modulated stimuli was constructed, with carrier rates between 140 and 300 Hz, and modulation rates between 60 and 150 Hz. The mo dulation rates were integer submultiples of the carrier rates, and each mod ulation period consisted of one higher-intensity pulse and one or mon ident ical lower-intensity pulses. The modulation depth of each stimulus was adju sted so that its pitch was judged to be higher or lower 50% of the time tha n that of an unmodulated pulse train having a rate equal to the geometric m ean of the carrier and modulation rates. A multidimensional scaling task wi th these ten stimuli resulted in two-dimensional stimulus spaces, with dime nsions corresponding to carrier and modulation rates. A further investigati on with one normally hearing subject showed that the perceptual weighting o f the two dimensions varied systematically with modulation depth. It was co ncluded that, when filtered appropriately, acoustic pulse trains can be use d to produce percepts in normal Listeners that share common features with t hose experienced by subjects listening through one channel of a cochlear im plant, and that the central auditory system can extract two temporal patter ns arising from the same cochlear location. (C) 1999 Acoustical Society of America. [S0001-4966(99)05501-0].