Influence of speech characteristics on working memory and perceived workload: Findings from experimental listening experiments

Journal article, 2027

Exposure to background speech is known to impair working memory performance, a concern particularly relevant in open-plan office environments. This study aimed to examine how specific characteristics of speech, including semantic content and sound pressure level, affect cognitive performance and perceived workload. Controlled laboratory listening experiments were conducted within a common experimental framework, allowing different acoustic characteristics of speech to be compared directly. Participants completed Operation Span tasks (OSPAN) while being exposed to binaural speech signals. Perceived workload was assessed using the NASA Task Load Index (NASA-TLX). In Listening Experiment A, the role of semantic content was investigated using conditions consisting of intelligible speech, locally time-reversed speech, continuous noise, and silence. Listening Experiments B1 and B2 focused on the effects of varying sound pressure levels in speech conditions. Overall, exposure to speech resulted in decreased cognitive performance relative to silence, whereas continuous noise and low-level speech yielded performance outcomes comparable to silent conditions. No significant effect of semantic content was observed in Listening Experiment A. In Listening Experiments B1 and B2, performance declined as sound levels increased, with diminishing effects observed at lower levels. Subjective workload ratings varied across conditions, even where objective performance differences were not detected. These findings suggest that background speech introduces a cognitive cost that may be compensated for in short term through increased mental effort, potentially contributing to long-term fatigue.