Perception thresholds of continuously approaching sound sources with rhythmic structures specific to biologically significant signals

摘要

Localization of biologically significant moving rhythmic sources with a different pulse-to-pause ratio is practically uninvestigated. The present study addresses the issue of what the perception thresholds of continuously approaching sound sources are. The approaching sound source (its illusion) was modeled by the noise pulse sequences linearly increasing in amplitude and transmitted through a loudspeaker located at the testee's head level, 1.1 m away, in the free field. The sequences consisted of short (5 and 10 ms) and long (70 and 100 ms) pulses. The thresholds of continuous movement were estimated by the interpulse pauses varying from 10 to 150 ms. For the short-pulse sequences the thresholds were 49 and 41 ms, while for the long-pulse sequences they decreased to 21 and 16 ms, respectively. The pause perception threshold of continuous movement was found to decrease consistently with the increasing pulse duration over the whole duration range tested. The period thresholds for the short-pulse sequences were 54 and 51 ms and did not differ significantly, while for the long-pulse sequences they were almost twice as high, 91 and 115 ms. For the structures representing the short (up to 10 ms) pulse sequences, the thresholds were highly variable in magnitude indicative of a probabilistic estimation of movement in the event of insufficient information. For the long (tens ms) pulse sequences, the threshold estimation stabilized. The thresholds of continuous movement and the effective masking time for the sound pulse sequences coincided, suggesting a leading role of consecutive masking in the estimation of movement continuity.