Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations.

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.