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原文摘要

Selective attention enhances cortical tracking of attended speech, but the role of ignored speech remains less clear. In particular, it is unknown whether attended and ignored speech contribute to cortical tracking in a fixed balance or whether this balance changes with listening conditions. We addressed this question across six electroencephalography (EEG) datasets spanning acoustic and attentional challenges, hearing impairment, and hearing-aid processing. We systematically varied the relative weighting of attended and competing speech and studied how their combined contribution affected cortical speech tracking. Across most listening conditions, cortical tracking was improved when we included competing speech, compared with attended speech alone. Importantly, the balance between attended and competing speech changed across conditions. Increasing acoustic difficulty increased both the benefit and the optimal contribution of competing speech, with the same general pattern observed in normal-hearing and hearing-impaired listeners. In the hearing-aid datasets examining noise-reduction conditions, the contribution of competing speech was more limited. Attentional challenges also changed the contribution of competing speech, but differently from acoustic challenges. These findings show that attended and competing speech do not contribute to cortical tracking in a fixed balance. Rather, their balance depends on the listening challenge. Although these results do not define a single optimal ratio, they provide a step toward hearing devices that adapt not only to the attended talker, but also to how competing speech is balanced in complex listening environments.