Improvable,yes; insoluble,no: A reply to Flock

The relationship between apparent size and apparent depth in certain forms of the Müller-Lyer illusion is explored both Experimentally and theoretically. The Experimental results show that the apparent Sizes and apparent distances of the Müller-Lyer shafts in the normal and in the “reverse” illusions are related to each other. They also contradict specific predictions About the apparent depth location of Müller-Lyer shafts derived from the Misapplied size-constancy theory and Emmert’s Law. These results are interpreted In terms of the operation of the size-distance Principle, and this interpretation is supported by observations of other illusions.