In search of invisible violence

NPR Radio covers an amazing inattentional blindness experiment that investigated how easy it is to miss a vicious beating in the street – after a policemen was convicted of ignoring an attack during a pursuit.

Inattentional blindness is the phenomenon where we don’t notice something seemingly obvious because we are paying attention to some other details.

It was most famously demonstrated by the ‘gorillas in our midst’ experiment where observers asked to count the number of passes between basketball players fail to notice a man in a monkey suit walking though the action.

Following a policeman’s conviction for supposedly ‘keeping quiet’ about a beating that he ran past while in pursuit of someone else, the same researchers wanted to know whether people asked to follow a jogger and monitor their behaviour would miss a simulated attack in the street.

Then about a minute in the run, slightly off to the side, [researchers] Chabris and Simons had three students stage a fight.

“We had two students beating up a third, punching him and kicking him and throwing him to the ground,” Chabris says.

The question was whether the students would see the fight, and under the conditions — nighttime — that most closely resembled [policemen] Conley’s experience. The numbers were shockingly low.

“Only about a third of the subjects reported seeing the fight that we had staged,” says Chabris.

It’s a brilliant piece of applied research, a great report with an amazing backstory, and the full text of the study is available online if you want more details.
 

Link to NPR report.
Link to full text of study.

Alice through the crooked glass

Not Exactly Rocket Science covers a fascinating study where participants felt they were the size of a doll or had expanded to giant proportions simply by using a headset, a camera and a bit of foot stroking.

In a typical experiment, a volunteer is being stroked while wearing a virtual reality headset. She’s lyng down and looking at her feet, but she doesn’t see them. Instead, the headset shows her the legs of a mannequin lying next to her.

As she watches, Bjorn van der Hoort, one of Ehrsson’s former interns, uses two rods to stroke her leg, and the leg of the mannequin, at the same time. This simple trick creates an overwhelming feeling that the mannequin’s legs are her own. If the legs belong to a Barbie, she feels like she’s the size of a doll. If the legs are huge, she feels like a 13-foot giant.

Van der Hoort performed this illusion on almost 200 people. Questionnaires revealed that they did indeed think of the mannequins as their own body parts. Familiar objects didn’t break the spell. When van der Hoort threatened the mannequins’ legs with a knife, the volunteers’ skin broke into a worried sweat, as if their real bodies were in danger. If he touched the doll’s legs with a pencil or his finger, the recruits thought they were being prodded by giant objects. Rather than feeling like dolls in a normal world, they felt like normal people in a giant world.

The researchers Not Exactly Rocket Science dub this the ‘Alice illusion’ after the changes in size experienced by the heroine in Alice in Wonderland.

These experiences can also be experienced as part of ‘Alice in Wonderland Syndrome’ which is usually associated with migraines or epilepsy (although they can occur without any brain disorder) likely due to them affecting the brain’s system for understanding the body’s relation to the surrounding space.

Temporary body-warping experiences are being created in the lab, however, in healthy normal folks and with surprisingly simple tricks.

The Not Exactly Rocket Science piece covers the latest delightful example.
 

Link to NERS on the ‘Alice illusion’.
Link to full text of scientific study.

Hearing the voices of colours

A spectacular case of psychosis, rather oddly described as ‘Methamphetamine Induced Synesthesia’, in a case report just published in The American Journal on Addictions.

The report concerns a 30-year-old gentleman from the Iranian city of Shiraz with a long-standing history of drug use who recently started smoking crystal:

Six months PTA [prior to admission] (October 2009), he started smoking methamphetamine once a day, and gradually increased the frequency to three times a day.

Two months PTA (January 2010), he developed symptoms of auditory and visual hallucinations (seeing fairies around him that talked to him and forced him to conduct aggressive behavior), self-injury, and suicidal attempts.

He developed odd behaviors such as boiling animal statues. He was hearing the voices of colors, which were in the carpet. Colors moved around and talked to each other about the patient. He also saw the heads of different kinds of animals gathering on a board, and they talked to him.

Finally, his mother brought him to the emergency room of Ebnecina Psychiatric Hospital in Shiraz.

The authors are using the term ‘synaesthesia‘ very liberally as it usually refers to an experience in one sense automatically triggering sensations in another – such as numbers having specific colours or tastes.

I’m not sure that ‘hearing the voices of colours’ necessarily qualifies as this could as much a delusion (a distorted belief) or a hallucination (that isn’t specifically tied to seeing the colours) rather than a genuine synaesthetic experience.

As the authors didn’t investigate any further and only have the gentleman’s word for his experiences, it’s a little hard to say.

However, it’s also worth noting that our concept of synaesthesia is no longer tied to ‘crossing of the senses’ as synaesthesia for increasingly meaningful things is being discovered.

Only recently, two confirmed and tested cases of ‘swimming-style synesthesia’ were reported in the journal Cortex where different colours were reliably triggered by the sight of people doing different swimming strokes.
 

Link to locked case report of ‘meth-induced synaesthesia’.

Poetic sensitivities

Perceptual psychologists have long been interested in limen – the threshold at which a stimulus becomes detectable. The following limen for the different senses, expressed in everyday terms rather than in terms of physical quantities, have a certain poetry to them. I got this information via email as a scan of an (unknown to me) textbook. I reproduce them here for your enjoyment:

Approximate absolute sensitivities, expressed in everyday terms:

Vision – A candle flame seen at 30 miles on a dark, clear night
Hearing – The tick of a watch under quiet conditions at 20 feet
Taste – One teaspoon of sugar in two gallons of water
Smell – One drop of perfume diffused into the entire volume of a three-room apartment
Touch – The wing of a bee falling on your cheek from a distance of one centimeter

Exact values vary between individuals and even from moment to moment with the same individual. Source: Galanter, E. (1962). Contemporary psychophysics. Holt, Rinehart, Winston.

A misperceptive critic

It’s not often that hallucinations indulge in media criticism, but this case of Charles Bonnet syndrome recently published in the journal Optometry is a delightful exception.

Everyone, it seems, is a critic, including perceptual distortions generated by, in this case, macular degeneration.

A 79-year-old man presented to the clinic with intermittent hallucinations of 6 months’ duration before this visit. He reported it occurred mostly in the evening, when he saw visions of road maps, Christmas wreaths, and faces that blocked his television screen. The faces were not of people known to him and often had elaborate hats or headdresses. When he rode in a car, he often saw houses that he knew were not truly present, and when he watched his favorite celebrity television dancing show, he saw multiple dancers rather than the 2 actually dancing. He was not disturbed or frightened by these hallucinations; he knew that they were not real. On the contrary, he felt they were amusing and reported they were often more entertaining than what was actually on television.

 

Link to PubMed entry for case report.
Link to DOI entry for same.

An illusory tribute

Richard Gregory was a much loved and hugely influential perceptual psychologist who passed away earlier this year.

Tom just alerted me to a wonderfully appropriate visual palindrome on his page of remembrance where his name reads perfectly well when either the ‘right way up’ on when ‘turned on its head’.

If you can’t see it or don’t believe it, go to the site and click the corner to see the image rotate.

A small but charming tribute to a man who used visual illusions to demystify perception.
 

Link to Richard Gregory tribute site.