New Optical Illusion – The “Expanding Hole” – How does it work?

This one is both fun and yet also interesting. The source is a newly published scientific paper, hence the scope here is not simply entertainment but rather it is being used as a tool to explore what is going on inside our brains.

First the illusion itself.

Look at the image below (You can find an even bigger version here) …

Most people, roughly about 86% of those that look at this, will see the black hole expanding as they look at it.

I’m in the 86% … so yes, wow.

But what is going on here, why do our eyes get tricked like that, and for that matter, where exactly did this new illusion come from?

Source is a new Scientific Paper

Published within the journal “Frontiers in Human Neuroscience” on May 30, 2022 and titled “The Eye Pupil Adjusts to Illusorily Expanding Holes“, the paper also comes with a press release that explains a bit of background to it.

There they quote the lead author, Dr Bruno Laeng, a professor at the Department of Psychology of the University of Oslo as follows …

“The ‘expanding hole’ is a highly dynamic illusion: The circular smear or shadow gradient of the central black hole evokes a marked impression of optic flow, as if the observer were heading forward into a hole or tunnel.”

“Here we show based on the new ‘expanding hole’ illusion that that the pupil reacts to how we perceive light – even if this ‘light’ is imaginary like in the illusion – and not just to the amount of light energy that actually enters the eye. The illusion of the expanding hole prompts a corresponding dilation of the pupil, as it would happen if darkness really increased,”

“Our results show that pupils’ dilation or contraction reflex is not a closed-loop mechanism, like a photocell opening a door, impervious to any other information than the actual amount of light stimulating the photoreceptor. Rather, the eye adjusts to perceived and even imagined light, not simply to physical energy. Future studies could reveal other types of physiological or bodily changes that can ‘throw light’ onto how illusions work,”

This is not just entertainment – there is some serious research going on here

At the root of this illusion is the observation that, in general, the perception of light is not straightforwardly related to physical parameters. Your brain constructs a model and also fills in gaps by interpreting the information it is receiving.

For example, you don’t have rods in your eyes to see color at the edges of what you see, your brain is filling in that gap.

The model within your brain will also result in physical responses to what that model is telling the brian. Within this illusion your brain is interpreting the illusion as an approaching darkness. The pupils in your eye expand to handle that coming darkness.

This is truly fascinating.

It basically tricks the response of your eye pupils … and so we learn our eye pupil response is managed, not by the actual lowering of light, but instead via the model that our brain creates in response to the data it receives.

Why is it like this?

It is a trait that we have been naturally selected for. Having eye pupils that respond in anticipation gives us a bit of an advantage.

Your brain is via the illusion looking ahead and anticipating that you are entering a dark area and so it preparing your visual system for that. Being plunged into darkness brings risk. Our ancestors have been naturally selected to have a visual system that anticipate darkness, adjusts, and so enabled them to see potential hazards.

The fact that it works like this means we pay a price. If we are not actually moving forward into a darker space, then our pupils have adjusted for no reason. Obviously the benefit here is far better than the cost, hence it gave us a survival advantage, so our vision works like this.

Some people in the study can’t see the illusion – why?

They speculate that this might be down to the model within their brain interpreting the image as an ink splash, hence their pupils did not respond by expanding.

Is it just us?

Would animals that have a similar visual system to ours also be susceptible to the same illusion?

We can only speculate. Personally I think they might.

Bottom Line

Our visual system is not simply like a photometer device that receives photons and reacts directly to that as it sends that data to your brain, there are layers of complexity here. Illusions are proving to be a truly fascinating tool to dig into all of that.

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