You've helped them one at a time. The real understanding is how the ideas CONNECT — teach that next.
Fade (the afterimage — persistence of vision; the visual trace left after a stimulus is removed) ×Loop (the perceptual motion loop — recursive, endless, barber-pole motion the brain sees)
A barber-pole seems to move endlessly upward, and a film looks like smooth motion. How do Fade and Loop explain both?
Fade then says: “The brain sees motion with no lingering trace between images; persistence of vision is not involved.” — is that right?
The link: lingering images blend together into the illusion of endless motion.
Each image lingers, and the brain sees it move.
Stack (the perspective trap — depth cues that mislead size judgments (Muller-Lyer, Ponzo)) ×Notch (the impossible figure — locally coherent but globally impossible (Penrose triangle, Escher staircase))
The Ponzo lines make one bar look bigger, and the Penrose triangle looks solid but cannot be built. What do Stack and Notch share?
Stack then says: “Perspective size-traps and impossible figures work by totally unrelated mechanisms.” — is that right?
The link: both trick the same depth-inference the brain makes from a flat picture.
Fool the depth cues, and size or solidity goes wrong.
Capstone — build one illusion together
Three kinds of illusion. Bring in the cast member for each.
Make a trace linger to fake motion. Who?
Who do you bring in?
Trick size with depth cues. Who?
Who do you bring in?
Draw a figure that cannot exist. Who?
Who do you bring in?
The synthesis: linger an image, fake the depth, and draw the impossible — three ways the brain can be fooled.
