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.

Temporal integration of rising and falling tone glides against a 50-2800-Hz background of noise at a sound pressure level of 60 dB re 20 micronPa was studied in two experiments. Glides were in the frequency ranges 200-700 Hz and 1200-1700 Hz for durations of 5-120 ms. Results indicate an asymmetry in the detectability of rising and falling glides of short duration, with rising glides detected at lower signal intensities in both frequency ranges. These effects are discussed in terms of differences in pattern of frequency analysis of identical, but temporally reversed, waveforms.

Temporal integration of fixed-frequency signals is a well-established phenomenon. However, integration characteristics for speech-like sounds are not known. The present study investigates temporal integration, in a background of noise, for fixed-frequency signals and rising and failing frequency contours in the ranges 200–700 Hz and 1200–1700 Hz. These ranges were chosen because of their correspondence to first-and second-formant regions for speech sounds. Tone glides changed frequency linearly during the burst durations of 5, 10, 35, 50, 90, and 120 msec. Reference fixed-frequency signals were selected at the extremes and arithmetic centers of the glide ranges (i.e., 200, 450, 700, 1200, 1450, and 1700 Hz). The results for fixed-frequency signals are in agreement with previous investigations. The integration rate of the falling higher-frequency tone glide is similar to that of the fixed-frequency signals. However, other tone glides indicate a slower rate of integration than for fixed-frequency signals. The results are interpreted regarding time and frequency limitations on the development of the critical band, and possible relevancy to speech perception. [Work supported in part by NIH.]

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