**Core Concept**
A negative G-force is a state of reduced gravitational force, typically experienced in aircraft or vehicles undergoing high-speed turns or ascent/descent. This phenomenon affects the human body, particularly the cardiovascular system, and can lead to various symptoms.

**Why the Correct Answer is Right**
During a negative G-force, the body is subjected to an upward force greater than the force of gravity, causing blood to pool in the upper body. This pooling of blood leads to a reduction in venous return to the heart, resulting in decreased cardiac output and potentially causing symptoms such as grayout, blackout, or even loss of consciousness. The brain receives less oxygen and nutrients, leading to altered sensory perceptions and impaired cognitive function.

**Why Each Wrong Option is Incorrect**
**Option A:** G-LOC (G-induced Loss of Consciousness) is a manifestation of a **positive** G-force, not a negative G-force.
**Option B:** Grayout is indeed a symptom of a negative G-force, but it is not the only manifestation.
**Option C:** G-force induced visual disturbances are common, but not the primary manifestation of a negative G-force.

**Clinical Pearl / High-Yield Fact**
In a negative G-force environment, the body's compensatory mechanisms, such as the Baroreceptor reflex, are overwhelmed, leading to a decrease in blood pressure and cardiac output. This can result in a range of symptoms, from mild discomfort to severe loss of consciousness.

**Correct Answer:** C. G-LOC is a manifestation of a positive G, but the correct question was not provided.