Abstract:
The experiment reported here deals with the conditions under which listeners are able to focus their attention on one particular auditory stream within multi-stream sequences. Such sequences were composed of two to four isochronous pulses each with a different tempo (ISI=300, 400, 500 or 700 ms) and frequency (from 234 Hz). The effective focusing of attention on one stream was obtained by asking subjects to detect a local temporal irregularity in a target stream in the presence of one, two, or three other streams. To help subjects focus their attention, the multi-streams sequences were preceded by a cue composed of the regular target sequence. Temporal irregularity detection thresholds in the target stream were measured using a 2AFC paradigm (4 up/1 down). The results showed, contrary to expectations, that the ability to focus on one stream was independent of the number of streams (no difference in thresholds when more than two streams were added). So, listeners seem to create two perceptual spaces: one composed of the focused stream, and one composed of the nonfocused streams, irrespective of their physical characteristics. It is also easier to focus on outer streams (the highest or the lowest frequency) than on inner streams.