Study: Pupil Size Changes with Breathing, Revealing Its Impact on How We Perceive the World
A recent study conducted by researchers at Karolinska Institutet in Sweden has uncovered a direct connection between breathing and pupil size. The findings show that the pupil contracts during inhalation and expands during exhalation, suggesting that respiration plays an active role in regulating how we take in and process visual information. This newly identified physiological mechanism provides fresh insight into the relationship between breathing and sensory adaptation.
The Study: How Scientists Uncovered This Phenomenon
As Neuroscience News reports, the study was led by Artin Arshamian, an associate professor at the Department of Clinical Neuroscience at Karolinska Institutet (Sweden). The findings were published in The Journal of Physiology.
The researchers conducted five meticulously designed experiments involving 200 participants. They measured pupil size changes using high-resolution eye-tracking technology while monitoring breathing patterns under various conditions. Participants engaged in both free and controlled breathing, with variations in breathing rate, mouth vs. nasal breathing, and exposure to different lighting conditions.
To ensure the robustness of their findings, the researchers conducted the experiments in different scenarios:
- Experiment 1 & 2: Participants were observed in dim lighting while maintaining a fixed gaze, first to establish the effect and then to replicate it.
- Experiment 3: The study expanded to include active visual tasks to determine whether the effect persisted during cognitive engagement.
- Experiment 4: Researchers tested controlled breathing at different paces under ambient lighting to measure variability.
- Experiment 5: To rule out the involvement of the olfactory bulb, participants with congenital anosmia (absence of an olfactory bulb) were included, confirming the mechanism’s independence from the sense of smell (people born without an olfactory bulb were included in the experiment to determine whether the influence of breathing on pupil size depends on olfactory pathways or is controlled by more fundamental neural mechanisms in the brainstem).
Across all conditions, the results consistently demonstrated that pupil size fluctuated in sync with breathing, revealing a fundamental and previously unknown regulatory mechanism of vision.
While prior research has suggested links between respiration and brain activity, this study is the first to definitively establish a connection between breathing and pupil size. Unlike the previously known factors affecting pupil size — light, focus, and cognitive factors —t his newly discovered mechanism is cyclical and does not require any external stimulus.
Key Findings of the Study
1. Pupil Size Fluctuates with Breathing
Pupils are at their smallest during inhalation and largest during exhalation. This suggests that natural breathing patterns influence visual perception.
Example: When performing activities that require fine detail, such as reading small print, breathing in can help improve perceptual clarity. Conversely, when performing a wide visual scan, such as when searching for an object in a dark room, exhaling can help improve detection.
2. Breathing Can Help Optimize Vision
The study suggests that inhalation sharpens focus on fine details, while exhalation improves the ability to detect objects in a wider field of view.
Example: An artist may benefit from inhalation when painting intricate details and exhalation when assessing the overall composition of their work.
3. The Brainstem Likely Controls This Mechanism
The discovery that the effect persists in individuals born without an olfactory bulb suggests that the brainstem, rather than olfactory-related brain structures, controls the pupil-breathing link.
Example: This insight helps neuroscientists better understand how breathing influences attention and perception beyond just olfactory-driven processes.
4. Consistent Across Different Conditions
The effect remained consistent across various breathing rates, mouth vs. nasal breathing, different lighting conditions, and visual tasks. This indicates that the phenomenon is a fundamental biological mechanism rather than a situational response.
Example: Whether someone is meditating, exercising, or performing a mental task, their pupil size will still fluctuate in sync with their breath.
5. Potential for Medical and Clinical Applications
Changes in pupil size could serve as a new diagnostic tool for neurological conditions, particularly disorders that affect pupil function, such as Parkinson’s disease.
Example: Early diagnosis of neurodegenerative diseases could be improved by monitoring how pupil size responds to breathing patterns.
Breathing’s Role in Attention and Mental Processing
Pupil size is closely linked to cognitive functions such as attention, alertness, and mental effort. Since breathing affects brain activity, this study suggests that breathing patterns might also influence attention regulation.
How Breathing Shapes Mental Focus
Pupil size has long been associated with cognitive load—expanding during intense concentration and contracting during relaxation. The new findings suggest that inhalation sharpens detail-focused vision, while exhalation broadens perception, which could help the brain switch between different modes of processing information.
For instance:
- Focused Attention: During tasks requiring precision, such as reading or threading a needle, inhalation may naturally enhance visual clarity.
- Broad Awareness: When scanning a crowd or navigating a dimly lit environment, exhalation may support the detection of peripheral or low-contrast objects.
Breathing Techniques and Cognitive Performance
These findings align with mindfulness and breathing exercises used in cognitive training. Controlled breathing techniques, such as deep nasal inhalation and extended exhalation, may help regulate attention and optimize cognitive performance. This could have implications for stress management, meditation practices, and even professional settings requiring sustained concentration.
From Research to Application: The Scientific and Medical Potential of the Findings
Scientific Significance
This discovery introduces breathing as the fourth fundamental factor influencing pupil size, alongside light exposure, near-focus adjustment, and cognitive or emotional responses, expanding our understanding of physiological and neurological processes. It highlights how subconscious biological rhythms, such as breathing, directly impact sensory processing and cognition.
Medical and Therapeutic Applications
- Neurological Disorders: Pupil response to breathing could serve as a biomarker for conditions such as Parkinson’s and other neurodegenerative diseases, aiding early diagnosis and monitoring.
- Attention and Focus Disorders: The connection between breathing and attention regulation suggests potential applications in managing ADHD and anxiety disorders through controlled breathing techniques.
- Visual Rehabilitation: Understanding how pupil size fluctuates with respiration could inform therapies for individuals with vision impairments or difficulties in focus adaptation.
Practical Recommendations
- Education & Work Environments: Incorporating structured breathing techniques into study sessions or work routines may improve focus and reduce cognitive fatigue.
- Athletic & Tactical Professions: Training athletes, pilots, and military personnel to control their breathing patterns may enhance situational awareness and response times.
- Mindfulness & Mental Well-being: Breathing exercises can be optimized for specific tasks—deep inhalation for focused tasks, extended exhalation for relaxation and situational awareness.
Conclusion
This study from Karolinska Institutet reveals a previously unknown link between breathing and pupil size, adding a new dimension to our understanding of vision and brain function. By uncovering this cyclical and ever-present mechanism, researchers have opened new possibilities for applications in neuroscience, medicine, and cognitive enhancement.
Future research may explore how this mechanism functions under various conditions, such as stress, fatigue, or altered states of consciousness. Understanding how breathing shapes perception and cognition could lead to practical applications in clinical treatments, cognitive training, and performance optimization across multiple fields.
