Reading: Multiple Choice: Question 5

Balance depends heavily on the vestibular system, a set of fluid-filled structures buried in the inner ear. Three semicircular canals, each oriented at roughly a right angle to the other two, detect rotational movement of the head in any direction by sensing the fluid inside them lagging slightly behind the skull as it turns. A separate pair of structures, the utricle and saccule, known collectively as the otolith organs, instead detect linear acceleration and the tilt of the head, using tiny crystals of calcium carbonate that shift against a gelatinous membrane studded with sensory hair cells.

Motion sickness is widely explained by what researchers call sensory mismatch theory. When the vestibular system reports that the body is moving, inside a car travelling over a winding road, for instance, but the eyes are fixed on something relatively still, such as the pages of a book or the interior of a cabin with no window, the brain receives two contradictory streams of information about whether the body is in motion. Because this specific pattern of conflicting signals resembles what the nervous system would expect from certain ingested toxins, the brain triggers nausea as a protective reflex, on the evolutionary logic that vomiting would expel a possible poison.

This theory also explains several familiar patterns. Symptoms often ease noticeably once a passenger looks toward the horizon, because a stable, distant visual reference realigns what the eyes report with what the vestibular system is already sensing, resolving the conflict rather than merely distracting from it. It may also explain why drivers report motion sickness far less often than passengers: a driver continuously anticipates the vehicle's next movement, which appears to help the brain reconcile the visual and vestibular signals before any conflict arises.

Susceptibility also varies considerably with age. Children under about two years old are rarely affected, most likely because their vestibular system is still developing and has not yet matured enough to generate a strong mismatch signal; sensitivity then tends to rise sharply, peaking around nine or ten years old, before gradually declining into adulthood. Some researchers have also documented a habituation effect: repeated exposure to the same provocative motion, such as a specific stretch of rough sea, can measurably reduce a person's sensitivity to it over successive trials, although the improvement appears to be specific to that particular motion rather than a general resistance to motion sickness overall.

Choose the correct letter, A, B, C or D.

1. According to the passage, what is the function of the otolith organs? A. They detect rotational movement of the head across three separate planes. B. They detect linear acceleration and the tilt of the head. C. They regulate the ear's sensitivity to loud sound. D. They filter fluid pressure inside the semicircular canals.

2. According to sensory mismatch theory, as described in the passage, motion sickness nausea is triggered because A. the stomach is directly damaged by repeated vibration during travel. B. the eyes become physically strained from tracking a moving scene too quickly. C. the vestibular system temporarily shuts down during unfamiliar motion. D. the brain interprets conflicting motion signals as a possible sign of poisoning.

3. Why does looking at the horizon often relieve motion sickness symptoms, according to the passage? A. It realigns the visual and vestibular signals so that they no longer conflict. B. It blocks the vestibular system's signals to the brain entirely. C. It slows the movement of fluid in the inner ear directly. D. It distracts the brain from processing any sensory input at all.

4. What does the passage say about susceptibility to motion sickness in children under two years old? A. They are more susceptible than any other age group. B. They experience symptoms of identical severity to adults. C. They are rarely susceptible because the vestibular system is still developing. D. Their susceptibility to motion sickness has never been studied.

5. What does the passage say about habituation to motion sickness? A. Habituation makes a person permanently immune to all forms of motion sickness. B. Habituation has been shown not to work under any circumstances. C. Habituation works only for airline passengers, not car passengers. D. Repeated exposure can reduce sensitivity, but the effect is specific to that type of motion rather than general.