Detection of linear frequency glides as a function of frequency and duration

This article compares frequency discrimination thresholds for four conditions, using a two-interval forced-choice task: (1) discrimination of a difference in center frequency for two pulsed tones (DLF); (2) discrimination of a steady tone from an up-frequency glide with the same mean frequency (UP-DL); (3) discrimination of a steady tone from a down-frequency glide with the same mean frequency (DOWN-DL); (4) discrimination of an up-frequency glide from a down-frequency glide with the same mean frequency (UPVSDOWN-DL). All glides were linear in Hz/s. Experiment 1 measured thresholds as a function of center frequency over the range 500–8000 Hz in 1-oct steps, for a fixed duration of 500 ms. The variation of glide thresholds with frequency was similar to that for the DLFs. Experiment 2 measured thresholds as a function of duration over the range 50–750 ms, for a fixed center frequency of 2000 Hz. The DLFs decreased monotonically with increasing duration. The glide thresholds decreased as duration increased from 50 to 100 ms, but did not change markedly beyond that. In both experiments, DLFs and UPVSDOWN-DLs were similar. UP-DLs and DOWN-DLs were typically two to three times greater than DLFs and UPVSDOWN-DLs, and UP-DLs tended to be larger than DOWN-DLs at center frequencies up to 2000 Hz. Experiments 3 and 4 measured thresholds for detecting glides in frequency when fixed glides in level were superimposed on all stimuli. The glides in level had only a small effect on the frequency-glide thresholds. The results are discussed in terms of their compatibility with Zwicker’s [Acustica 6, 365–381 (1956)] excitation-pattern model of modulation detection and in terms of their implications for sampling theories of glide detection.