Final answer:
The term for losing peripheral vision during high G maneuvers is 'tunnel vision,' which describes the narrowing of the visual field to only what is directly ahead, resembling the view through a tunnel.
Step-by-step explanation:
The loss of peripheral vision during high G maneuvers is commonly referred to as tunnel vision. When a pilot or an individual is subjected to high gravitational forces, blood flow is affected, which can lead to a decrease in the visual field. The vision narrows so that the individual may seem as if they are looking through a tunnel, mainly seeing what is directly in front of them while losing the peripheral parts of their visual field. While bilateral hemianopia is a condition associated with the loss of lateral peripheral vision due to a growth on the pituitary gland pressing against the optic chiasm, tunnel vision in the context of high G maneuvers is caused by the body's physiological response to the G forces, not a growth or other physical condition.