The study of illusions provides unique insights into how our brains construct normal, everyday perceptual experience. Illusions are studied at different levels of analysis, from psychophysical perspectives (i.e., quantifying what we see) to neuroanatomical perspectives (i.e., describing and quantifying how we see). The Müller-Lyer illusion falls into the class of distortion illusions. Specifically, this illusion will distort your perception of size. To learn more, follow the link below.
ON TO MÜLLER-LYER ILLUSION