Which illusion stems from a pilot's misjudgment of their altitude due to a lack of visual references?

The height-depth illusion occurs when a pilot misjudges their altitude chiefly due to the absence of visual references, particularly during nighttime or in low visibility conditions. This situation can lead to a perception that the aircraft is either higher or lower than it actually is, which can have serious implications for flight safety. The lack of distinct ground features or lighting that typically provide reference points makes it difficult for a pilot to accurately gauge their altitude.

In contrast, the other options relate to different visual perceptions that do not specifically address the misjudgment of altitude due to absent references. Structural illusions are more about how structures may appear differently depending on context. Size constancy is the perception of an object's size remaining constant despite changes in distance, while size-distance illusions involve the distortion of perceived size based on context, not altitude interpretation. Understanding the height-depth illusion is crucial for pilots to mitigate the risks associated with flying in conditions where visual reference points are minimal.