What is one effect of -Gz on the body?

The correct response addresses one of the significant physiological impacts of -Gz, or negative gravitational forces, particularly during maneuvers in aviation that involve rapid descent or negative "G" forces. When experiencing -Gz, the body is subjected to forces that push blood away from the brain, leading to a condition known as G-induced Loss Of Consciousness (GLOC) or visual disturbances.

Under these negative acceleration forces, blood can pool in the upper body, reducing cerebral perfusion pressure and resulting in visual impairment or loss. Pilots may experience tunnel vision or even a complete blackout due to the reduced blood flow and oxygen delivery to the brain.

The other options describe situations that do not occur under -Gz conditions. For example, clarity of thought and focus, as well as stability in vision, would be adversely affected rather than enhanced in negative G situations. Blood pooling in the upper body does occur, but it is not a direct effect of the -Gz force itself on the brain, making it less accurate in this context.