Your pupils constrict when you count silently in your head, revealing the presence of 'inner speech'.
April 1, 2026
Original Paper
Dissociable pupil-linked arousal during overt and inner speech
bioRxiv · 10.64898/2026.03.29.715074
The Takeaway
While speaking out loud consistently dilates the pupils, thinking silently produces a strikingly different physical reaction: constriction. This reveals that the brain enters a fundamentally different arousal state during silent thought, providing a non-invasive way to 'see' when someone is talking to themselves.
From the abstract
Inner (covert) speech, the silent production of language in one's mind, plays a central role in human cognition and is known to activate speech-related cortical regions while also requiring executive and attentional resources. However, the conventional focus on cortical similarity or dissimilarity between inner and overt speech leaves unaddressed the question of whether arousal systems sustain cortical language processing. Here, using pupillometry across three controlled counting experiments, we