[Thresholds of continuously approaching sound sources with rhythmic structures typical for biologically significant...

Localization of biologically significant moving rhythmic sources with different pulse/pause ratio has been practically not investigated. The issue of the perception thresholds of continuously approaching sound sources is addressed in the present study. The illusion of approaching sound courses was created by noise pulse sequences linearly increasing in amplitude and emitted by a loudspeaker placed at the level of the subject's head, 1.1 m away, under free field conditions. The sequences were formed by short (5 and 10 ms) or long (70 and 100 ms) pulses. The continuous movement thresholds were evaluated by the pauses between noise pulses varying from 10 to 150 ms. For the short pulse sequences the thresholds were 49 and 41 ms, while for the long ones they decreased to 21 and 16 ms, respectively. A progressive decay of the continuous movement perception threshold in pausing between noise pulses with increasing width over the whole pulse-width range studied was observed. The thresholds for the short noise pulse sequences were 54 and 51 ms did not differ significantly, while for the long noise pulse sequences they were almost twice as long, 91 and 115 ms. For the structures representing the short (up to 10 ms) pulse sequences, the thresholds were highly variable in magnitude that is indicative of a probabilistic evaluation of movement in case of insufficient information. For the long (tens of ms) pulse sequences, the threshold evaluation was stabilized. The continuous movement thresholds and the effective masking time for sound pulse sequences coincided suggesting critical role of non-simultaneous masking for the evaluation of movement continuity.