Your pupils change size depending on how you are thinking

Researchers at the University of Tsukuba in Japan wanted to compare inner speech, the voice in your head, with overt speech, talking out loud. Volunteers did simple counting tasks: counting in order (1, 2, 3), counting with objects (one dog, two dogs), and counting in intervals (1, 3, 5). They did each task both silently and aloud while the team measured their pupil dilation. Pupils dilated during every out-loud task. During silent tasks, though, the response depended on the task: pupils constricted for simple counting, dilated for interval counting, and did not change for others. The study, published in iScience, could help scientists understand how children's language develops.