Slide 1: the areas within the two red circles are the same shade of grey

Slide 2: the circle on the right will gradually disappear as progressively lighter rings appear around it 2

Slide 3: as slide 2, but the grey background appears only at the end of the sequence

Slide 4: as slide 2, but the rings converge inwards instead of spreading outwards

Slide 5: the chessboard illusion; the small circles are all the same shade, although they look very different

Slide 6: the chessboard illusion; a small chunk migrates from one circle to another, to demonstrate that they are the same shade

Slide 7: another chessboard illusion; the black square in light and the white square in shadow are the same shade; this is demonstrated by a bar that extends from one to the other