Vision

When you look at this painting, what do you see? A woman looking out a window? How about now?

This famous painting by Salvador Dali is based on something called the ‘Lincoln illusion‘. The effect shows how blurring pixelated images can make it easier to recognise faces. Optical illusions are fun to look at, but, they can also tell us a lot about our sense of sight.

So, how does the eye work exactly, and is it really true that seeing is believing?

The human eye is pretty extraordinary. It has more than 2 million moving parts and can move faster than any other muscle, at less than 1/100th of a second.

But when it comes to your vision, the way you perceive the world is actually thanks to your brain.

• First, light enters the eye through the pupil.
• The muscles behind the iris squeeze and stretch the lens to focus the light onto the back of the eye. This is the retina.
• The retina is covered with sensitive photoreceptors called rods, for dim light, and cones, for bright light.
• The focused light hits the retina at a small pit called the fovea, which has the highest density of cone receptors.

We often compare our eyes to cameras, but they actually work quite differently.

• Our peripheral vision is very low resolution.
  • We only see in full resolution at the small point of our fovea, but we barely notice it because our eyes are constantly refocusing on what we want to see, like a high-resolution spotlight.
• Pixels, or picture elements, are the tiny, illuminated squares that make up a digital display.
  • If two pixels are close to your eye, the retina sends two signals for the brain to interpret.
  • Farther away, two pixels prompt one signal. That’s why a TV screen can have a lower pixel density than a smartphone, but seen from farther away, it still appears seamless.
• When stimulated, the rods and cones send signals to the optic nerve and back to the brain.
  • Then, all of that visual information is processed to create the picture you see of the world.
• Unlike a camera, your brain can actually “fill in” missing information.
  • For example, your eyes automatically blink every 3 to 4 seconds.
  • In fact, that means your eyes are technically closed for roughly 10% of your waking hours.
  • Thankfully, your brain fills in those gaps, so you don’t feel like the lights are flickering on and off all day long.

There’s a lot we still don’t understand about the complexities of our visual system.

As technologies continue to innovate, the line between illusion and reality could start to blur. And when it comes to how we see the world, there might be more than meets the eye.

Watch the centre of this disk. You are getting sleepy. No, just kidding. I’m not going to hypnotize you. But are you starting to see colours in the rings? If so, your eyes are playing tricks on you. The disk was only ever black and white.

You see, your eyes don’t always capture the world as a video camera would. In fact, there are quite a few differences, owing to the anatomy of your eye and the processing that takes place in your brain and its outgrowth, the retina.

Let’s start with some similarities.

• Both have lenses to focus light and sensors to capture it, but even those things behave differently.
  • The lens in a camera moves to stay focused on an object hurtling towards it, while the one in your eye responds by changing shape.
• Most camera lenses are also achromatic, meaning they focus both red and blue light to the same point.
  • Your eye is different – when red light from an object is in focus, the blue light is out of focus.

So why don’t things look partially out of focus all the time?

To answer that question, we first need to look at how your eye and the camera capture light: photoreceptors.

• The light-sensitive surface in a camera only has one kind of photoreceptor that is evenly distributed throughout the focusing surface.
  • An array of red, green and blue filters on top of these photoreceptors causes them to respond selectively to long, medium and short wavelength light.
• Your eye’s retinas, on the other hand, have several types of photoreceptors, usually three for normal light conditions, and only one type for lowlight, which is why we’re colourblind in the dark.
  • In normal light, unlike the camera, we have no need for a colour filter because our photoreceptors already respond selectively to different wavelengths of light.
• Also in contrast to a camera, your photoreceptors are unevenly distributed, with no receptors for dim light in the very centre.
  • This is why faint stars seem to disappear when you look directly at them.
• The centre also has very few receptors that can detect blue light, which is why you don’t notice the blurred blue image from earlier.
  • However, you still perceive blue there because your brain fills it in from context.
• Also, the edges of our retinas have relatively few receptors for any wavelength light.
  • So our visual acuity and ability to see colour falls off rapidly from the centre of our vision.
• There is also an area in our eyes called the ‘blind spot‘ where there are no photoreceptors of any kind.
  • We don’t notice a lack of vision there because once again, our brain fills in the gaps.

In a very real sense, we see with our brains, not our eyes. And because our brains, including the retinas, are so involved in the process, we are susceptible to visual illusions.

Here’s another illusion caused by the eye itself.

• Does the centre of this image look like it’s jittering around?
• That’s because your eye actually jiggles most of the time.
• If it didn’t, your vision would eventually shut down because the nerves on the retina stop responding to a stationary image of constant intensity.
• And unlike a camera, you briefly stop seeing whenever you make a larger movement with your eyes.
  • That’s why you can’t see your own eyes shift as you look from one to the other in a mirror.
• Video cameras can capture details our eyes miss, magnify distant objects and accurately record what they see.
  • But our eyes are remarkably efficient adaptations, the result of hundreds of millions of years of coevolution with our brains.

And so what if we don’t always see the world exactly as it is?

There’s a certain joy to be found watching stationary leaves waving on an illusive breeze, and maybe even an evolutionary advantage. But that’s a lesson for another day.

How long to look

• There’s no set duration – observe for as long as feels comfortable
• Beginners might start with 3-5 minutes
• Changing perspectives or closing your eyes briefly can help maintain focus
• In guided experiences, this can extend to 10-60 minutes

What to look at

• Anything!
• Slow looking can happen anywhere – museums, outdoors, or even with mundane items like stamps or grass
• Look with fresh eyes and continually discovering new details

Solo vs. group ‘slow looking’

• Both solo and group slow looking have benefits.
• Solo observation improves focus and memory, while group observation allows participants to build on each other’s insights.
• Sharing observations fosters deeper understanding and sparks new ideas.

Beyond looking and thinking

• Slow looking can be done through creative practices like sketching, drawing, or even observing through microscopes.

• You can also sketch or use drawing activities to enhance observation, as well as writing your observations down.