What function is primarily assessed by testing cranial nerve VIII?

Cranial nerve VIII, also known as the vestibulocochlear nerve, is primarily responsible for two key functions: hearing and balance. The cochlear component of this nerve is involved in transmitting sound information from the inner ear to the brain, enabling the perception of sounds. Meanwhile, the vestibular component plays a crucial role in maintaining balance and spatial orientation by providing information about head position and motion.

When assessing cranial nerve VIII, healthcare providers typically conduct various tests to evaluate both hearing and balance. Audiometric tests can be performed to assess hearing capability, while balance assessments might include tests such as the Romberg test or evaluating the body's response to changes in position.

The other functions mentioned in the options pertain to different cranial nerves: vision is assessed by cranial nerve II, taste sensation is associated with cranial nerves VII and IX, and facial sensation is primarily evaluated through cranial nerve V. Therefore, testing cranial nerve VIII specifically focuses on hearing and balance, making it the correct choice.