Answer:
Illusions indicate that the brain does not totally rely on the eye to make visual perceptions of reality. It sometimes generates perceptions of reality based on assumptions of how it should be.
Step-by-step explanation:
Our brains and eyes together with the optical nerves linking them together, form part of the complex visual system of the body.
An illusion occurs when there is a mismatch between the perceived reality by the brain and the actual reality of what exists. Whenever this happens, it shows that some of the time, the brain does not always rely on a complete optical signal/information from the eye in order to make a perception. The brain at times tends to "complete the image" using the little information available alongside personal experiences and this often leads to misperception.