What visual cue informs aviators about aircraft speed and direction of movement?

Motion parallax is the correct response because it refers to the way objects appear to move relative to one another as the observer's position changes—primarily in relation to depth and speed. In an aviation context, as an aircraft maneuvers, elements in the cockpit or external terrain will move relative to the speed and direction of the aircraft. For instance, objects closer to the aircraft will seem to move faster across the field of view than those that are farther away. This visual cue helps aviators gauge their aircraft's speed and direction during flight, improving their situational awareness.

Other options, while relevant in specific contexts, do not directly assist in accurately determining the speed and direction of movement of an aircraft. False horizon can lead to misinterpretation of the aircraft's orientation, autokinesis might cause a pilot to misjudge the position of external lights or objects, and fascination/fixation can lead to distraction from important peripheral cues. Thus, motion parallax stands out as the most effective visual cue for assessing movement.