Effect of spatial discontinuity on short-term memory for melodic sequences

We investigated whether spatially separating segments of a tone sequence split the sequence into separate perceptual streams, and whether it affected how pitch information was stored in memory. Listeners heard a sequence of six 300-ms complex tones presented either to a single ear, or with the first three and last three tones presented to different ears. They reported whether a subsequent monaural probe tone matched a tone in the original sequence, based solely on pitch (disregarding the ear to which the probe was played). Overall, performance was higher when the probe tone matched either the first or one of the last two tones in a target compared to when the probe matched more interior target elements. For single-ear target sequences, presentation of the probe in the opposite ear diminished performance compared to when it was presented in the same ear as the target. Spatially splitting the target sequence had very little effect. The results suggest that the tone sequences were perceived as a single stream, irrespective of whether there was spatial discontinuity. However, a probe in an unexpected location confused listeners, perhaps causing a spatial attention shift that diminished the already-weak memory representation of the interior tones' pitches.