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Science

Binocular Rivalry Experiment

Can aphantasia be objectively measured?

For most of us, visualizing thoughts, past memories, or images of the future is a ubiquitous part of our human experience. For a small group of people, the experience of mental imagery is entirely unknown. Otherwise healthy people can completely lack the experience of visual or other sensory imagery, a condition now referred to as aphantasia.

To determine whether someone is aphantasic or not, many researchers will conduct an initial evaluation using the Vividness of Visual Imagery Quiz (VVIQ), which asks you to rate the vividness of different scenarios to test the strength of your visual imagery. VVIQ is a proven psychometric for measuring individual differences in visual imagination and is considered a reliable self-assessment for identifying aphantasia.

Until recently, however, it was unclear to scientists whether people were unable to imagine visually, or if they have images in their mind but are simply blind to them. To objectively address this question, a team of researchers from UNSW lead by Dr. Joel Pearson conducted studies using the Binocular Rivalry (BR) experiment and a technique called perceptual priming.

What did they discover? Aphantasics show almost no imagery-based rivalry priming. These results confirm that aphantasia is a lack of sensory imagery and not a lack of metacognition.

Binocular Rivalry and How it Works

When our eyesight is blurry, it seems obvious that we would go get our eyes tested. When we suspect that the mental image inside our mind’s eye is hazy, it isn’t so easy. Without an objective measurement, it can be difficult to say for sure what is actually going on.

How can a doctor possibly see what is happening in someone else’s mind to the degree of accuracy needed to make a diagnosis? As far as aphantasia goes, scientists have actually found one way to test whether someone cannot visualize people, objects and settings in their mind’s eye. The technique is called perceptual priming, and it uses a phenomenon known as binocular rivalry.

When light enters our eyes, it sends information to our brain about what is happening in the world around us. The brain collects visual data from both eyes and essentially overlaps the information to show us one combined image of the world. When both eyes receive completely different sensory information, however, the brain can get confused. At this point, rather than overlap the images from both eyes, only one image will take dominance over the other, and that is the image that you will see.

This is known as binocular rivalry – literally, two eyes competing. It is a phenomenon of visual perception in which perception alternates between different images presented to each eye.

For example, see the red and blue image of a horse below. If you look at the image through glasses where one lens is red and one lens is blue (like the old-school 3D glasses) the red horse will only be seen through the red lens and the blue through the blue lens. The eyes will then compete as to which colour will be seen.

Some people will only see blue while some people will only see the red horse.

Binocular Rivalry
Illustration by Holly-Anne Drowne. Red and Blue Horse (3D Effect): Behance

Interestingly, if you visualize the colour blue in your head before the picture is shown to you, it becomes more likely that that is the picture and colour you will see. This is known as ‘perceptual priming’ because it prepares or primes the brain to see that image or colour. As you can probably guess, perceptual priming doesn’t work for aphantasics – they can’t visualize the colour in their mind, so their brain won’t be primed, and they won’t be any more likely to see one image than the other.

To test for aphantasia, you can induce binocular rivalry at home and see if there is any correlation between perceptual priming and what you actually perceive.  If you do have aphantasia, then thinking about the colour will not make it any more likely that you will see it. If you do not have aphantasia, you will be able to visualize the colour and should find that you’re more likely to physically see the image of the colour you’re imagining.

How to Conduct Binocular Rivalry Experiment at Home

Part One

You will need a pair of red-blue glasses. Old-school 3D theatre glasses should work! This will make sure that the red image will only make it through the red lens, and the blue image will only make it through the blue lens. This sends different sensory input to each eye and stimulates binocular rivalry.

Review the images in this article, where two images are superimposed over each other. One image is red and the other is blue. Stabilize your head by resting your chin on something sturdy – a stack of books on your table works perfectly! Put on the glasses and scroll through the three images in this article. Then answer the following question: Which image is more dominant red or blue? Record your answers.

Once you have gone through all three images on this page answer: How many times did you see the red image, how many times did you see the blue image, and how many times was it unclear? Record your results.

Binocular Rivalry
Illustration by Helmo. Kangaroo-Zebra: Brad Wilson/Getty Images.

Part Two

Now, conduct the same experiment again. Only this time try specifically thinking about the colour red. Try to imagine it in your mind, if you can. Repeat the exercise while thinking about the colour red. Record your results. Compare results and share them in the comments below.

Binocular Rivalry
Illustration by Helmo. Rabbit-Leopard: Brad Wilson/Getty Images.

What the Results Could Mean

Compare the results from part one with the results from part two. If you found that you saw the red image much more frequently than the blue one in part two,  then it is unlikely that you have aphantasia. This is because you have primed your brain to see the red image most of the time, a phenomenon that tends not to work on those with aphantasia.

Did you find it difficult, if not impossible, to visualize the colour red in your mind in part two? If you couldn’t visualize the colour in your mind, your brain was not expecting to see the red image in the same way than it would if you were able to visualize it. This means you saw results in part two that were pretty similar to part one. If that is the case, then this could mean you have aphantasia.

This is a simple experiment that can often provide you with more insight into your unique experiment, but like any experiment, it is not perfect. The more times you do try it with different images, the more accurate your results will be. Try it again and again, see more images here. Did your results change or not change? 7 or 8/10 times is usually a good indicator. Report your findings in the comments below.

Quantifying human imagination

Mental imagery is just one of several key dimensions of human imagination, and the binocular rivalry technique is just one of many possible objective measures for evaluating mental imagery strength, and whether someone has aphantasia or not.

Our dedicated team at the Aphantasia Network is currently collaborating with world-leading scientists and experts in mental imagery to develop new digital tools for quantifying human imagination. Want to be among the first to test out new products, features and measurements to gain a greater understanding of your unique imaginative experience? Sign-up for our newsletter!

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