The Checker-Shadow "illusion" Part 2.

Around 15-20 years ago I had this sudden insight, a sudden understanding. It was pertaining to so-called perceptual illusions.  I suddenly realised that many so-called perceptual illusions are not in fact illusions at all. Close to ten years ago I wrote a blog post regarding the checker-shadow illusion where I explained that, in my opinion, properly speaking, this is not in fact an illusion at all. Before reading further I recommend that people read that blog post. I would also recommend that people read another blog post by me on perceptual illusions here.   And, although not necessary to read, this blog post too might be of interest.  

On searching on the net I've only ever been able to find one person who holds the same opinion as I do that this shadow-checker "illusion" is not in fact an illusion at all.  And that was merely on a discussion forum.  Indeed, I have been vehemently attacked on this issue by many people (although it is clear to me they simply completely fail to understand my argument). Anyway, just a couple of days ago, I discovered a very interesting review of a book regarding colours and which talks about the checker-shadow illusion.  It says:

“Illusion” implies that our system is fooled, but as far as useful information goes, the checkerboard interpretation is probably better. Try as they might, mathematicians can’t make the computers see the checkerboard. Rather than a demonstration of how easily fooled we are, optical illusions like this one are examples of the brain’s mysterious and irreplicable abilities. It interprets its environment with a sophistication that exceeds our ability to measure and reconstruct physical phenomena. The usual framing has it wrong: Despite A and B having the same SSR, humans are still able to see the checkerboard.

First of all, it's gratifying to at last find someone else that agrees with me.  Two other people actually, both the author of the book and the reviewer.

But, anyway, this underscores the fact that in certain respects computers, at least if merely using visual information, cannot see as well as we do.  The fact that computers cannot see the checkerboard implies that they cannot see their environment very well at all.  This is why autonomous cars can't just rely on cameras but require other sensing methods such as LIDAR.  It also partially explains why fully autonomous cars might still be decades away.  Back in 2014 I predicted 2060, which at that time was vastly later than all the predictions of the various pundits.  Almost to the man they thought that fully autonomous cars would be widespread within 5-20 years.

So, despite using highly sophisticated algorithms, computers still cannot see as well as we do.  An interesting question is why can't they?  Why can't they see the checkerboard?  If it is merely the brain that enables us to see, then whatever physical processes are involved, they surely should be able to be matched by suitably sophisticated algorithms.  To me their failure in this regard suggests that something else is required, that consciousness in and of itself  is playing a pivotal role that is enabling us to see proficiently.

Are Perceptual illusions always necessarily illusions?

I'm sure that all of us are astounded that the squares A and B are actually the same colour. It is the shadow cast over B by the cylinder which makes us think otherwise. What this suggests is a quite incredible illusion.

However I think there is a pervasive naivety about the nature of perception. Most of us doubtless feel that we see the external world directly. But we emphatically do not.

Consider a red rose. We think of a red rose as being the same colour throughout the day. However the light from the Sun reaching the Earth varies throughout the day. When the Sun is low in the sky, lots of blue light gets scattered away since the sunlight has to travel through a greater quantity of air. So if we were to passively see colours "as they really are", then the colour of our red rose would change throughout the day. Indeed the colour of all objects would change throughout the day. But in fact our rose seems to stay pretty much the same colour throughout the daylight hours. Why is this?

The answer lies in the fact that we do not in fact simply passively see what is out there. Rather the brain performs certain operations on the data coming through our senses and presents it to our consciousness in a form that we can make sense of. Everything we ever see is in fact a hypothesis about how the world is. Thus we have an implicit theory about the external world that it contains objects which have specific intrinsic colours. Hence the brain will perform those operations which ensure that objects do indeed appear to be the same colour throughout daylight hours.

This applies not just to colours, but everything we perceive through our 5 senses. In a way then everything we ever perceive is an illusion. But I think this is misleading.

Let's consider the "illusion" above again. If this were a real 3D object and we were to approach it and view it from various angles, then we would see that squares A and B are very different colours. Indeed their intrinsic colours would be precisely as we perceive them in the illusion above.

But in that case what justifies us in labelling it as an illusion? If this were a real object that we are seeing, then squares A and B are very different colours. Our senses are not deceiving us. Indeed if someone claimed to see the squares as being precisely the same colour, then it is doubtful that he could proficiently visually apprehend his environment.

This is not to say we never perceive illusions. Sometimes we seem to see something, but which on closer inspection turns out to be something else entirely. Or sometimes what we seem to visually see is not consistent with our other senses.

Edited to add:  I have a follow up to this post written many years later:  The Checker-Shadow "illusion" Part 2.