Effects of temporal grouping on the memory representation of inter-tone relationships

The length of silence between successive sounds is a dominant cue for temporal grouping of sounds. The present study tested whether the sensory memory representation of inter-tone relationships is dependent on the grouping of tones within a single stream of sound. Subjects were presented with sequences of two alternating tones that differed from each other in frequency. Perception of a sequence made up of tone-pairs was promoted by alternating a short and a long inter-tone interval. Occasional tone repetitions fell either within one tone-pair or across two pairs. We found that detecting tone repetitions was slower for across- than within-pair repetitions (Experiment 1). Also the amplitude of the mismatch negativity (MMN) event-related potential was lower for across-pair repetitions compared with that measured in the control isochronous sequences (Experiment 2). This attenuation of the MMN-amplitude could not be explained by the inter-tone interval differences that existed between the paired and the isochronous conditions (Experiment 3). These results demonstrate that temporal grouping affects the sensory memory representation of inter-tone relationships within a single sound stream.