Dissociable pupil-linked arousal during overt and inner speech

Inner (covert) speech, the silent production of language in one's mind, plays a central role in human cognition and engages speech-related cortical networks partly overlapping with those for overt speech. Because cortical language processing unfolds within arousal states set by the ascending systems, we asked whether inner and overt speech are accompanied by similar pupil-linked arousal patterns. Using pupillometry across three counting-task experiments, we found a dissociation between inner and overt speech. While overt speech consistently elicited pupil dilation across conditions, inner speech produced a variable dilation profile relative to baseline: pupil constriction (simple counting), no deviation (noun-phrase counting), and clear dilation (step counting; high cognitive load). Importantly, pupil size during inner speech remained smaller than that during overt speech despite task-dependent dynamics. These findings suggest that task-elicited inner speech is accompanied by lower pupil-linked arousal than overt speech, adding a state-level physiological dimension to cortical accounts of verbal processing.