Science & Tech · Science & Environment · 1 hr ago
Study Finds Inner and Spoken Speech Affect Pupils Differently
Researchers in Japan found that speaking aloud and talking silently in your head affect pupils differently.
They tested 80 healthy university students as they counted aloud or silently while researchers measured their pupil size.
Speaking aloud consistently made pupils grow larger, a change that can offer clues about brain arousal.
Silent counting had mixed effects: pupils narrowed during simple counting, showed no significant change when students counted objects, and grew larger during harder step counting.
The silent response changed with the mental effort required, unlike the consistent response to speaking aloud.
The findings suggest that vocalizing is linked to pupil-related arousal, while inner speech usually involves a different response.
A study in iScience found that speaking aloud and speaking silently in one’s head produce different pupil responses.
Researchers monitored the pupils of 80 healthy university students during three counting experiments.
Speaking aloud consistently caused pupils to dilate, while silent inner speech produced mixed responses.
During silent counting, pupils constricted in the simplest task, showed no significant change in the second task and dilated during the most difficult task.
The researchers said the findings suggest vocalization is an important factor in pupil-linked arousal.
- Who
- Researchers in Japan, led by neuroscientist Ryuta Kuwamizu and developmental psychologist Ryoichi Watanabe, studied 80 healthy university students.
- What
- The study examined pupil responses during spoken and silent counting.
- When
- Published on 2026-10-25. The study date is not stated.
- Where
- Japan; the researchers were from the University of Tsukuba and Ritsumeikan University.
- Why
- To investigate how inner speech relates to the brain’s arousal systems.
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- Participants
- 80 healthy university students
- Experiments
- 3 counting tasks
- Simple task
- Counted upward using consecutive integers
- Most difficult task
- Counted in randomized increments of 2, 3, or 4
- Publication
- iScience
1 source
What people are saying
The presence of vocalization is an important factor shaping pupil-linked arousal.
This dilation likely reflects the integrated pupil-linked arousal recruitment associated with motor execution, respiratory variation, sensorimotor feedback, and attention, each of which is presumed to engage brainstem arousal systems and cortical network states, potentially contributing to efficient speech production.