The consistency of task-relevant and task-irrelevant vocal cues modulates speech judgments during dichotic listening

During speech perception, listeners simultaneously process various vocal cues (such as identity information like the speaker's sex or age, or expression cues like confidence), yet it remains unclear which type of information receives prioritized processing. This study systematically examines how attentional task goals modulate the interaction between task-relevant and task-irrelevant cues, and how this interplay shapes the hierarchical processing of speech-related dimensions such as identity (e.g., sex or age) and expression (e.g., confidence). The current study utilized a dichotic listening paradigm across two experiments to investigate how identity and expression information in vocal cues are processed, focusing on the role of attentional relevance. Participants listened to two vocal stimuli simultaneously in each ear and were instructed to focus on either identity (manipulated by speaker sex in Experiment 1 and age in Experiment 2) or expression (varying levels of confidence). In this study, task-relevant information consistency across ears refers to the consistency of target judgment information (e.g., sex in the sex judgment task) between the left and right ears in dichotic listening, while task-irrelevant information consistency across ears refers to the consistency of non-target judgment information (e.g., confidence in the sex judgment task) between the two ears. When attending to identity, consistent identity cues between ears led to faster responses and higher accuracy. However, when attending to expression, response times showed no significant difference across expression consistency, but accuracy improved when identity cues were consistent-even though identity was task-irrelevant. These findings suggest a functional prioritization of vocal identity over expression during speech processing, highlighting the hierarchical and goal-dependent nature of vocal cue extraction. The asymmetrical effects of processing task-relevant and task-irrelevant information, depending on vocal cues, emerge when identity processing is less demanding than expression evaluation, suggesting the functional priority of vocal identity over vocal expression in multiple displays during speech perception.