Which effect does severe vibration have on crewmembers?

Severe vibration can significantly impact the sensory and physiological functions of crewmembers, particularly their vision. When subjected to intense vibrations, the visual system can be destabilized, leading to difficulties in focusing properly and resulting in blurred vision. This occurs because the vibrations can disrupt the alignment and movement of the eyes, making it challenging for individuals to maintain clear eyesight, especially during critical tasks that require visual acuity.

In contrast, the other options suggest effects that are generally not associated with severe vibrations. For instance, concentration is likely to decrease rather than improve under such conditions due to the distraction and discomfort caused by vibrations. Similarly, severe vibrations tend to impair, rather than enhance, audio perception because sounds can become distorted and harder to hear clearly amidst the noise generated by vibrations. Additionally, endurance is often decreased when experiencing severe vibration, as the physical toll on the body can lead to fatigue and decreased performance over time. Thus, the correct understanding of severe vibration's effects aligns with how it contributes to blurred vision among crewmembers.