Gretchen was walking through the park and noticed a large hole in the sidewalk ahead of her. As she approached the hole, she realized it was just a chalk drawing creating the illusion of a three-dimensional hole. The hole appeared to show a river (colored with blue chalk) flowing far below some jagged rocks (colored with grey chalk).

Gretchen stopped to take a picture with the drawing, where it looked like she was falling down the hole. The artist saw Gretchen taking photos and introduced herself. The artist explained that her optical illusion was created using monocular perception cues.

Part A Explain how the artist might have used each of the following to create the illusion. Linear perspective

Interposition Relative

size Texture

gradient

Part B Explain how each of the following concepts helped Gretchen see the artwork. Trichromatic theory

Occipital lobe

Accommodation