Category: Illusions

Audio Technique Makes People Feel That Their Doppelganger Is In The Room With Them

By Emma L. Barratt

Hallucinatory experiences are pretty common, despite widespread beliefs to the contrary. Researchers estimate that around 40% of the population regularly experience hallucinations to some degree, whether that be feeling your phone vibrate only to find no notifications, or a full-on out of body experience.

Though hallucinations are common, some are harder to study than others. One of the trickiest has been autoscopic hallucinations, during which people experience a doppelganger of all or part of their body in the space around them.

Though this hallucination has been reported to clinicians, its rarity has made it difficult to observe in an experimental setting — so researchers have instead attempted to induce the phenomenon in the lab. Now, Marte Roel Lesur and team at the University of Zurich have developed a way to experimentally induce it in people who have no history of hallucinations using only auditory cues.

Continue reading “Audio Technique Makes People Feel That Their Doppelganger Is In The Room With Them”

We Think We’ve Changed More In The Past Than We Will Change In The Future — And Americans Seem Particularly Susceptible To This Illusion

By Emma Young

Think about what you were like 10 years ago. How have you changed, in terms of values, life satisfaction and personality? Now picture yourself 10 years in the future. Do you think you’ll be just as different then as you were a decade in the past?

When asked about past vs future change, most people — no matter what their age — report more change over a period of time in the past than they predict for the same period into the future. This “End of History Illusion” has been well-documented, at least, among WEIRD populations. Now Brian W. Haas at the University of Georgia, US, and Kazufumi Omura at Yamagata University, Japan, report some cultural differences in susceptibility to it. Their paper, in Personality and Social Psychology Bulletin, also provides some intriguing hints as to why those differences exist.

Continue reading “We Think We’ve Changed More In The Past Than We Will Change In The Future — And Americans Seem Particularly Susceptible To This Illusion”

Cats Like To Sit In Squares — Even Ones That Are Really Optical Illusions

By Emma Young

The world is not exactly short of videos of cute cats up to strange antics. But one particular set of videos collected by cat owners during a COVID-19 lockdown reveals something genuinely interesting: a famous optical illusion that fools us also gets cats. The citizen science project, in which cats were experimented on in their own homes, shows that they, too, are tricked by “Kanizsa squares”, an illusion that suggests the presence of a square that doesn’t in fact exist.

Continue reading “Cats Like To Sit In Squares — Even Ones That Are Really Optical Illusions”

This Weird, Sound-Induced Illusion Makes You Feel That Your Finger Has Grown Longer

By Emma Young

Adults are vulnerable to all kinds of body illusions. We can be made to feel that a fake hand, or even a fake body, is our own; that we’ve left our body; even that we’re the size of a doll. These illusions work because our brains use information from various senses to create mental representations of our bodies. Mess with some of these sensory signals, and you can alter those representations, sometimes drastically.

Work to date suggests that young children don’t show the same susceptibilities to body illusions, presumably because the systems that underpin them are still developing. Now a new study, published in Scientific Reports, has found that a bizarre auditory-induced illusion that affects adults doesn’t work in quite the same way in young kids, either.

Continue reading “This Weird, Sound-Induced Illusion Makes You Feel That Your Finger Has Grown Longer”

Here’s The First Evidence That Even Lizards Succumb To Optical Illusions

Central bearded dragon on the rock

By Emma Young

It’s been known for centuries that we experience all kinds of optical illusions, and in the past few decades, researchers have shown that some animals, including monkeys, pigeons, and dogs, do too. Now the first ever study of this kind in reptiles has found that even the bearded dragon falls for an optical illusion that we humans succumb to.

Perceptual illusions — subjective interpretations of physical information — are interesting to psychologists because they reveal important insights into how we construct our representations of the world. This new work, published in the Journal of Comparative Psychology, provides evidence that at least one reptile can be counted among the animals don’t simply passively process retinal signals, but actively interpret visual data, too.

Continue reading “Here’s The First Evidence That Even Lizards Succumb To Optical Illusions”

A psychologist noticed this cool chair illusion in his office

10.1177_2041669517752372-fig1.gifBy Alex Fradera

A short paper in the journal i-Perception presents a disconcerting visual illusion spotted “in the wild”: how stackable chairs, viewed from a certain angle, mess with your head. This is an unedited image, but your mind resists accepting it could be real. The illusion was first noticed in the office of lead author Nick Scott-Samuel at the University of Bristol, who notes in the paper that “it obtains in real life as well as in images, even when sober”.

The cause of the trick appears to be the two “edges” seen coming up from the near-base of the stack – marked AD and BC in the annotated version of the image below – which “suggests a change in depth along those lines which does not actually exist” and makes it seem as if the bars that run from one “edge” to another compose an outward face.


160px-Penrose-dreieck.svg.pngIt misleads us a little like the Penrose triangle (see right), but whereas the triangle is actually impossible, the chairs only appear to be so – as demonstrated in this video where you can see the effect dip in and out. Scott-Samuel and his colleagues experimented with the chair stack and it appears that you need at least four chairs to create the effect.

You know the angles, you know the number: turn up to the meeting room early next time and use that recipe to astound even the most jaded eyes.

Stacking Chairs: Local Sense and Global Nonsense

Alex Fradera (@alexfradera) is Staff Writer at BPS Research Digest

Believers in conspiracy theories and the paranormal are more likely to see “illusory patterns”

GettyImages-177765632.jpgBy Emma Young

Democratic bankers caused the global financial crisis to get Barack Obama elected. 

Horoscopes are right too often for it to be a coincidence. 

Irrational beliefs – unfounded, unscientific and illogical assumptions about the world – are widespread among “the population of normal, mentally sane adults” note the authors of a new study in European Journal of Social Psychology. It’s been proposed that they arise from a mistaken perception of patterns in the world. But though this idea is popular among psychologists, there’s been surprisingly little direct evidence in favour of it. The new work, led by Jan-Willem van Prooijen at the Free University of Amsterdam, helps to fill the void.

Continue reading “Believers in conspiracy theories and the paranormal are more likely to see “illusory patterns””

Investigating the weird effects treadmills have on our perception

Treadmill workoutBy Christian Jarrett

Anyone who’s been on a treadmill at the gym has probably had that strange perceptual experience afterwards – once you start to walk on stable ground again, it feels for a time as though you’re moving forward more quickly than you really are. The illusion, which is especially striking for treadmill newbies, was first documented scientifically in a Nature paper 20 years ago. Since then psychologists have come to better understand what’s going on and the ways the effects can manifest. Continue reading “Investigating the weird effects treadmills have on our perception”

First brain scan study to feature THAT dress

Figure and caption from Schlaffke et al., 2015.

Earlier this year a dress nearly broke the internet. A photo of the striped frock (which is actually blue and black) was posted on Tumblr and it quickly became apparent that it looked very different to different people, spawning furious arguments and lively scientific commentary.

Specifically, people disagreed vehemently over whether it was white and gold (that’s my perception) or blue and black. Now, writing in the journal Cortex, researchers in Germany have published the first study to scan people’s brains while they look at the dress, and the neural findings appear to support earlier, psychological explanations of the phenomenon.

When the dress story went viral, psychologists were quick to explain that this dress provided a striking example of how our perception of the world arises from a combination of incoming sensory information and our interpretation of that information. In the case of colour perception, when light bounces off an object and hits your retina, its mix of wavelengths is determined by the colour of the object and the nature of the light source illuminating it. Your brain has to disentangle the two. Usually it does this very well allowing for something called “colour constancy” – the way that objects of the same colour are perceived the same even under different illumination conditions. However, the mental processing involved in colour perception does leave room for interpretation and ambiguity, especially when the nature of the background illumination is unclear as is the case with the photo of the dress (another illusion that hacks the limitations of this aspect of our visual system is the checker shadow illusion).

For the new study, Lara Schlaffke and her colleagues scanned the brains of 28 people with normal vision while they looked at the photo of the dress. Fourteen of the participants see the dress as white and gold and 14 see it as blue and black. The key finding is that the people who see the dress as white and gold showed extra activation in a raft of brain areas, including in frontal, parietal (near the crown of the head) and temporal (near the ears) regions. Yet, no group differences emerged in a control condition when the participants simply looked at large coloured squares that matched two of the colours that feature in the dress, but without any contextual information also visible (see figure, above).

These results are broadly consistent with the idea that the white/gold perceivers were engaged in more interpretative mental processing when looking at the dress. To oversimplify, their perceptual experience of the dress is based less purely on the “bottom up”, raw sensory information arriving at their eyes, and is distorted more by their own assumptions and expectations about the background illumination. The extra activity in their brains during the dress viewing is likely, at least in part, a neural correlate of all this interpretative, “top down” processing.

What the new study can’t answer is whether this extra neural processing (or which aspects of it) in the white/gold group is the cause of their perceptual experience of the dress, or the consequence. However, the researchers describe some future approaches that could help address this quasi-philosophical conundrum: for example, by using transcranial magnetic stimulation (TMS) to temporarily disrupt the extra localised neural activity seen in the people who experience the dress as white and gold, we could ask: will they still experience the illusion?

Meanwhile, as someone who’s firmly in the white/gold camp, I take satisfaction from this study: I might see the dress as the “wrong” colours, but at least this isn’t due to simple-mindedness, but rather it’s because my brain’s working overtime, doing clever tricks in the background. I’m pretty sure that must be an advantage in at least some situations.


Schlaffke, L., Golisch, A., Haag, L., Lenz, M., Heba, S., Lissek, S., Schmidt-Wilcke, T., Eysel, U., & Tegenthoff, M. (2015). The brain’s dress code: How The Dress allows to decode the neuronal pathway of an optical illusion Cortex, 73, 271-275 DOI: 10.1016/j.cortex.2015.08.017

further reading

Visual illusions foster open-mindedness

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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