The homunculus model says that all visual perception factors through an image constructed in the brain. One should be able to reconstruct this image by asking a subject to compare the brightness of pairs of checkerboard squares. A simplistic story about the optical illusion is that the brain detects the shadow and then adjusts the brightness of the squares in the constructed image to exactly compensate for the shadow, so the image depicts the checkerboard’s inferred intrinsic optical properties. Such an image would have no shadow, and since that’s all the homunculus sees, the homunculus wouldn’t perceive a shadow.
That story is not quite right, though. Looking at the picture, the black squares in the shadow do seem darker than the dark squares outside the shadow, and similarly for the white squares. I think if you reconstructed the virtual image using the above procedure you’d get an image with an attenuated shadow. Maybe with some more work you could prove that the subject sees a strong shadow, not an attenuated one, and thereby rescue Abram’s argument.
Edit: Sorry, misread your comment. I think the homunculus theory is that in the real image, the shadow is “plainly visible”, but the reconstructed image in the brain adjusts the squares so that the shadow is no longer present, or is weaker. Of course, this raises the question of what it means to say the shadow is “plainly visible”...
I expect our subjective “darkness ordering” is actively inconsistent, not merely an attenuated shadow (this is why I claim it can’t be depicted by any one image we would imagine the homunculus seeing).
But now I see that an attenuated shadow is consistent with the obvious remarks we might make about subjective brightness. Maybe we need to compare subjective ratios (like “twice as bright”) to illustrate the actual inconsistency.
(My subjective experience seems inconsistent to me, but maybe I’m making that up.)
The shadow looks “pretty dark” to me. When I ask myself whether it is darker or lighter than the difference between light and dark squares, I get confused, and sometimes snap into seeing A and B as the same shade.
Here’s a fun and pointless way one could rescue the homunculus model: There’s an infinite regress of homunculi, each of which sees a reconstructed image. As you pass up the chain of homunculi, the shadow gets increasingly attenuated, approaching but never reaching complete invisibility. Then we identify “you” with a suitable limit of the homunculi, and what you see is the entire sequence of images under some equivalence relation which “forgets” how similar A and B were early in the sequence, but “remembers” the presence of the shadow.
The homunculus model says that all visual perception factors through an image constructed in the brain. One should be able to reconstruct this image by asking a subject to compare the brightness of pairs of checkerboard squares. A simplistic story about the optical illusion is that the brain detects the shadow and then adjusts the brightness of the squares in the constructed image to exactly compensate for the shadow, so the image depicts the checkerboard’s inferred intrinsic optical properties. Such an image would have no shadow, and since that’s all the homunculus sees, the homunculus wouldn’t perceive a shadow.
That story is not quite right, though. Looking at the picture, the black squares in the shadow do seem darker than the dark squares outside the shadow, and similarly for the white squares. I think if you reconstructed the virtual image using the above procedure you’d get an image with an attenuated shadow. Maybe with some more work you could prove that the subject sees a strong shadow, not an attenuated one, and thereby rescue Abram’s argument.
Edit: Sorry, misread your comment. I think the homunculus theory is that in the real image, the shadow is “plainly visible”, but the reconstructed image in the brain adjusts the squares so that the shadow is no longer present, or is weaker. Of course, this raises the question of what it means to say the shadow is “plainly visible”...
Thanks for putting it so well!
I expect our subjective “darkness ordering” is actively inconsistent, not merely an attenuated shadow (this is why I claim it can’t be depicted by any one image we would imagine the homunculus seeing).
But now I see that an attenuated shadow is consistent with the obvious remarks we might make about subjective brightness. Maybe we need to compare subjective ratios (like “twice as bright”) to illustrate the actual inconsistency.
(My subjective experience seems inconsistent to me, but maybe I’m making that up.)
Elaborating:
The shadow looks “pretty dark” to me. When I ask myself whether it is darker or lighter than the difference between light and dark squares, I get confused, and sometimes snap into seeing A and B as the same shade.
Here’s a fun and pointless way one could rescue the homunculus model: There’s an infinite regress of homunculi, each of which sees a reconstructed image. As you pass up the chain of homunculi, the shadow gets increasingly attenuated, approaching but never reaching complete invisibility. Then we identify “you” with a suitable limit of the homunculi, and what you see is the entire sequence of images under some equivalence relation which “forgets” how similar A and B were early in the sequence, but “remembers” the presence of the shadow.