Abstract

The Irrelevant Sound Effect (ISE) commonly refers to the disruption of short-term memory tasks by task-irrelevant background sound. Although the ISE is known to be particularly strong with unpredictable and acoustically complex speech, the role of prosodic properties remains underexplored. This paper reports online experiments investigating how two pitch dimensions—acoustic regularity related to pitch change (regular vs irregular) and directional movement (rises vs falls)—influence the ISE. The regular stimuli were deemed more acoustically complex than the irregular stimuli, although this characterisation is debatable. Participants completed short-term memory tasks while they were exposed to manipulated speech strings. The results showed that irregular pitch variation was more disruptive than regular patterns, but no difference was found between rises and falls. Traditionally, recall performance was assumed to be directly determined by the acoustic parameters of background sound. However, our results suggest that an unpredictable distribution of perceptually salient acoustic events captures attention and disrupts short-term memory performance. We propose a functional approach grounded in predictability and perceptual grouping rather than spectral change for advancing our understanding of the ISE.