Perceived continuity and pitch perception

Three experiments investigated the importance of perceived stimulus continu ity For the perception of the fundamental frequency (F0) of an unresolved c omplex tone. The F0 of the complex was 250 Hz and the harmonics were bandpa ss filtered between 5500 and 7500 Hz. In the first experiment, F0 discrimin ation was measured for single-burst tones with durations of 20, 40, and 80 ms, and for stimuli containing two 20- or 40-ms tone bursts separated by an 8- or 16-ms gap. For the single-burst conditions, there was a large decrea se in threshold as the duration was increased from 20 to 40 ms. However, pe rformance in the gapped conditions was much worse than that for the single- burst condition with the same cumulative duration (e.g., two 20-ms bursts s eparated by 8 ms produced higher thresholds than one 40-ms burst). Adding a bandpass noise (with the same spectral envelope as the tone) in the gap be tween the two tone bursts improved performance to the level of the single-b urst condition. When the noise was added, the two discrete tone bursts were perceived as one single tone burst interrupted by the noise, and this seem ed to facilitate discrimination. Tn a second experiment, the effects on pit ch of an envelope delay (phase shift) of 0.75 periods between two tone burs ts separated by an 8-ms gap were investigated. If the gap was silent, the p itch of the pair was unaffected by the phase shift. However, if the gap con tained the bandpass noise, the phase shift between the bursts did produce a significant downward shift in the pitch of the pair. Finally, the third ex periment showed that presenting a noise before a single 20-ms burst may imp rove discrimination performance in some listeners, but not sufficiently to account for the results of the first experiment purely in terms of an impro vement in the discriminability of the second tone burst in the pair. The ex periments suggest that a level decrease between two tone bursts may disrupt or reset a long integration mechanism, decreasing performance. When there is no level decrease between the bursts, the auditory system may assume tha t the two bursts belong to the same single tone and analyze them together i n order to derive F0. (C) 2000 Acoustical Society of America. [S0001-4966(0 0)00209-5].