In the Ponzo illusion, which factor primarily causes one line to appear longer than the other even though both lines are physically equal in length?

• A. The brightness of the lines makes one appear longer than the other.
• B. The orientation of the lines causes the illusion.
• C. The use of converging lines creates a sense of depth, leading to misperception of size.
• D. The color contrast between the lines alters perceived length.

Answer: (C)

Verified step by step guidance

1. Understand that the Ponzo illusion is a visual illusion where two lines of equal length appear to be different lengths due to the context in which they are presented.
2. Identify the key visual elements involved in the Ponzo illusion, specifically the presence of converging lines (like railway tracks) that create a sense of depth or perspective.
3. Recognize that the converging lines trick the brain into interpreting the upper line as being farther away, and because of size constancy mechanisms, the brain perceives the farther line as longer even though both lines are physically equal.
4. Eliminate other factors such as brightness, orientation, or color contrast, as these do not primarily cause the misperception in the Ponzo illusion.
5. Conclude that the primary cause of the illusion is the use of converging lines creating a depth cue, which leads to the misperception of size and length.