Pitch of Nonuniformly Spaced Pulses in Periodic Trains

Abstract

The stimulus under study had a waveform consisting of 2 equal-amplitude pulses per fundamental peiod. Subjects signified the pitch of this challenge stimulus by matching it with a training of uniformly spaced pulses. Independent variables of the challenge were period duration T, intraperiod pulse spacing τ, and pulse polarity (++ or +−). Signal sensation level was 30 dB at 100 pps. All pulse durations were 25 μsec. The acoustic transducers were PDR-8 earphones connected binaurally in phase. Results for the ++ stimulus show: Challenge rates less than about 100 pps produce, with respect to the challenge, pitch matches which change gradually from pps/2 to pps as τ increases from 0 to 5–8 msec; for these same rates and for all other τ, the match is pps; challenge rates greater than about 165 pps exhibit sharp pps/2-to-pps transitions at the constant ratio τ/T=0.47. For the +− case, pps/2-to-pps transitions occur with increasing τ at challenge rates as high as about 265 pps; for a 420-pps challenge, as τ ranges from near 0 to T/2, the matches shift from pps/2, to approximately pps, and back to pps/2. These results provide further insight concerning the relative potencies of harmonic and pulsive components of auditory signals.