Feeling nauseated when attempting to read a book or look at a phone screen in a moving vehicle stems from motion sickness. This discomfort is a physical manifestation of confusion within the central nervous system. The root cause is a fundamental disagreement between the body’s sensory systems, which send contradictory information to the brain about whether the body is moving or stationary. This internal conflict triggers the uncomfortable symptoms associated with car sickness.
Sensory Conflict: The Brain’s Interpretation
The explanation for motion sickness is the sensory conflict theory, which posits that the brain receives mismatched signals from the systems responsible for spatial orientation. When these inputs do not align with the brain’s expected pattern of movement, it registers a state of confusion. One set of signals indicates movement, while another insists the body is still, creating a perceptual mismatch.
This confusion triggers an ancient, protective mechanism within the brain. Evolutionary theory suggests that, historically, sensory conflict was often the result of ingesting neurotoxins that caused visual or balance hallucinations. To protect the body, the brain’s automatic response is to induce nausea and vomiting to expel the perceived poison. This defense mechanism causes the feeling of queasiness when reading in a car.
The Vestibular System’s Role in Detecting Motion
The primary source of the “we are moving” signal is the vestibular system, a sensory organ located deep within the inner ear. This system is composed of the semicircular canals and the otolith organs, which detect motion and changes in head position. The three semicircular canals are filled with fluid and tiny hair cells, or cilia, that sense rotational movement, such as turning corners or tilting the head.
The otolith organs, the utricle and saccule, contain small, calcium carbonate crystals that rest on a gelatinous membrane. When the vehicle accelerates, decelerates, or changes vertical position, the inertia causes these crystals to shift. This movement bends the sensory hairs beneath them, sending a distinct signal to the brain that the body is in motion, even though the passenger may be sitting still.
Why Focusing on a Stationary Object Causes Problems
The visual system works in harmony with the vestibular system to provide a complete picture of the body’s spatial orientation. When a person is reading, their eyes are fixed closely on a stationary object, whether it is a physical book or a digital screen. The visual field, therefore, does not register the external movement of the car.
The eyes send a “we are still” signal to the brain because the text on the page remains stable relative to the head. This visual input directly contradicts the strong, persistent “we are moving” message coming from the inner ear. The brain attempts to reconcile these two opposing reports—movement perceived by the vestibular system and stillness perceived by the visual system—resulting in the sensory conflict that manifests as motion sickness.
Strategies to Reduce Motion Sickness While Traveling
The most effective way to prevent motion sickness is to minimize the sensory conflict by aligning the visual and vestibular inputs.
- Stop reading and focus your gaze on a distant, fixed point outside the vehicle, such as the horizon. This allows the visual system to confirm the motion sensed by the inner ear, reducing the mismatch.
- Sit in the front passenger seat, which provides a broader view of the road ahead, enabling the eyes to anticipate and track the vehicle’s movement.
- Keep the vehicle cool by opening a window to allow for fresh airflow, which can alleviate symptoms of nausea.
- If symptoms begin, closing your eyes or taking a short nap can eliminate the conflicting visual input, often providing immediate relief.