Abstract:

The irrelevant speech effect (ISE)—performance disruption caused by task-unrelated speech—is well established in simple language processing tasks. Far less consensus exists for complex language processing, where multiple operations (e.g., lexical recognition, syntactic parsing, semantic integration, inferential reasoning) are jointly engaged. Clarifying whether the ISE generalizes to such tasks, how large it is under realistic cognitive load, what sources and pathways of interference drive it, and which conditions modulate it is essential for theory building across attention, working memory, and language comprehension, as well as for applied domains where background speech is pervasive (classrooms, open-plan offices, and multimedia learning environments).
This study had three aims: to estimate the overall magnitude of the irrelevant-speech effect (ISE) in complex language-processing tasks; to assess the strength of evidence for the phonological- and semantic-interference hypotheses (sources of interference) as well as for the process-interference hypothesis (pathway of interference); and to identify moderators, individually and jointly, that account for discrepant findings in the literature. To address these aims, a random-effects meta-analysis was conducted in which 30 studies contributing 113 independent effect sizes on complex language processing under irrelevant speech were synthesized. The random-effects framework accommodated between-study heterogeneity arising from differences in populations, task characteristics, and speech properties. Heterogeneity was interrogated via subgroup analyses for categorical moderators and meta-regressions for continuous moderators, followed by tests of moderator interactions.
The results revealed four main findings. First, at the broadest level, irrelevant speech yielded a small but reliable decrement in performance on complex language tasks, indicating that the effect generalized beyond simple language processing. Second, semantic interference produced greater disruption than phonological interference, providing stronger quantitative support for the semantic-interference account and pointing to competition at the level of meaning. The evidence also provided moderate support for a process-interference mechanism. Third, effect sizes were systematically modulated by key conditions: participant age group (children and young adults were more susceptible than older adults), intelligibility of the irrelevant speech (meaningful speech produced significantly greater interference than meaningless speech), loudness (loud irrelevant speech significantly impaired performance), predictability (interference decreased from halfalogues to monologues to dialogues), type of “meaningless” speech (phonotactically well-formed nonsense yielded greater interference than other sounds), and task type (greater in memory than in comprehension or recognition). Finally, consistent with the central role of intelligibility, robust interactions emerged: intelligibility interacted with age group (children and young adults showed a significant difference between meaningful and meaningless speech; older adults did not), with task type (a difference appeared only in comprehension, not in memory or recognition), with the linguistic unit targeted (a difference appeared only at the sentence and discourse levels, not at the word level), and with the writing system (greater interference for meaningful than meaningless in logographic scripts; the same pattern held but was smaller in phonographic/alphabetic scripts).
Theoretically, this study advances the literature by delineating “complex language-processing tasks.” It provides a comprehensive assessment of how irrelevant speech interferes with them and tests, in complex settings, the applicability of theoretical models originally proposed for simple language-processing tasks. Moreover, results demonstrate a clear quantitative advantage for semantic-interference accounts over phonological accounts and provide moderate support for process-interference mechanisms. Furthermore, the rationale for selecting moderator variables is detailed in this study, their moderating effects and the interactions among key variables are analyzed in depth, and the sources of inconsistency in prior findings on the ISE are identified (e.g., variation in the materials used for “meaningless” background speech). Finally, this study indicates that logographic scripts likewise exhibit an irrelevant speech effect comparable in magnitude to that observed for phonographic scripts.
Practically, these findings can inform implementation by offering guidance on the use of audio, video, and other modern educational technologies to support language learning in contemporary multimedia instruction; proposing approaches to design and optimize learning environments that mitigate interference from background noise; and providing theoretical guidance and support for developing more effective interventions and treatments for individuals with cognitive impairments.

Key words: Irrelevant Speech Effect, language processing, interference mechanisms, meta-analysis