What change occurs in the vestibular system due to prolonged weightlessness?

In a state of prolonged weightlessness, such as experienced by astronauts in outer space, the vestibular system—responsible for maintaining balance and spatial orientation—undergoes significant changes. The correct answer, altered perception of motion, reflects how the absence of gravity affects the body's usual cues for balance and orientation.

In normal conditions, the vestibular system relies heavily on gravitational forces to interpret motion and position. When these forces are removed, the body can become disoriented because the usual reference points that help in determining movement and stability are no longer present. This can lead to a condition known as space adaptation syndrome, where astronauts may experience dizziness, nausea, and a distorted sense of motion as their brains struggle to reconcile the unfamiliar sensation of weightlessness with the expected cues from the vestibular system.

The other choices do not accurately reflect the physiological changes encountered in microgravity. While coordination and balance might initially be affected negatively, leading to decreased performance in those areas, the perception of motion becomes particularly altered as the brain seeks to adapt to a lack of gravitational stimuli. Decreased sensitivity to sound is unrelated to the function of the vestibular system, as it is primarily responsible for balance and spatial orientation rather than auditory processing.