Psychology Blog

Apologies if updates are a little irregular, as I’m currently on my way back to the UK for a three week visit. This is largely because I’ve been asked to speak to the ‘All-Party Parliamentary Group on Scientific Research in Learning and Education’ about the evidence for whether computer games are damaging kids’ brains. I kid you not.

I shall also use the opportunity to catch up with the fantastic research group I’m associated with at the Institute of Psychiatry, but I’ll largely be sleeping on sofas, floors, buses, park benches and the like, so do forgive any irregularity or incoherence (although regular Mind Hacks readers seem quite well accustomed to both by now, and for some of you, I suspect it’s part of the attraction).

More here:
Back to blightly

The San Francisco Exploratorium is the Mind Hacks of science museums - every exhibit is hands on, giving you the chance to experiment with and experience for yourself scientific principles.

Obviously, one of my favourite exhibits was a psychology demonstration, one based on a classic visual illusion known as the “Ames’ Room”. We’ve a small model of this in Sheffield, which I use when teaching PSY101, but the Exploratorium’s “distorted room” is full size demonstration of the effect. Here’s me and a friend in the room:

Notice anything odd? We’re the same size in reality, but I (on the right) look significantly larger.

The illusion takes advantage of the unavoidable principle that size and distance are confounded - known as “Emmert’s Law“. It is Emmert’s Law that means that big things far away can look the same size as small things near by. Our brain makes assumptions about how far away things are and uses these to inform our impression of size. The distorted room is built so that, from one perspective only, the two sides of the room look an equal distance away. In fact, the corner on the right is far closer to the viewer (the camera in this case) than the corner on the left. Because I really am nearer the camera I make a larger image on the retina (take up more pixels on the camera), but because the brain assumes that I am the same distance away as my friend on the left the only conclusion that my visual system can draw is that I must be much larger than him.

Normally your visual system isn’t fooled about depth - clues in the scene, the difference between the image on your two eyes and movements of your head can all help reveal how far away different parts of the scene are. The distorted room removes some of these clues by forcing you took look at the room with one eye from a fixed point, and other clues it deliberately tricks (like the shape of tiles on the floor, which look the same from left to right, but actually get smaller, because the tiles on the right are closer).

The confounding of size and distance is the same principle behind illusions like this:

The effect only works because it is in a photograph (so from one perspective) and because the relatively featureless desert removes other clues to the depth of objects.

So the next time you close one eye and line up someone in the distance between your thumb and forefinger while muttering “I’m crushing your head!“, think of Emmert’s Law. And if you are in San Francisco, visit the Exploratorium!

Here is the original post:
In the Exploratorium’s distorted room

Cannabis smokers often report that when stoned, their thoughts have a free-wheeling quality and concepts seem connected in unusual and playful ways. A study just published online in Psychiatry Research suggests that this effect may be due to the drug causing ‘fast and loose’ patterns of spreading activity in memory, something known as ‘hyper-priming’.

Priming is a well studied effect in psychology where encountering one concept makes related concepts more easily accessible. For example, classic experiments show that if you see the word ‘bird’ you will react more quickly to words like ‘wing’ and ‘fly’ than words like ‘apple’ and ‘can’ because the former words are more closely related in meaning than the latter.

In fact, it has been shown that the more closely related the word, the quicker we react to it, demonstrating a kind of ‘mental distance’ between concepts. Think of it like dropping a stone into a pool of mental concepts. The ripples cause activity that reduces in strength as it moves away from the centre.

‘Hyper-priming’ is an effect where priming happens for concepts at a much greater distance than normal. For example, the word ‘bird’ might speed up reaction times to the the word ‘aeroplane’. To return to our analogy, the ripples are much stronger and spread further than normal.

The effect has been reported, albeit inconsistently, in people with schizophrenia and some have suggested it might explain why affected people can sometimes make false or unlikely connections or have disjointed thoughts.

As cannabis has been linked to a slight increased risk for psychosis, and certainly causes smokers to have freewheeling thoughts, the researchers decided to test whether stoned participants would show the ‘hyper-priming’ effect.

The experiment used a classic ‘lexical decision task‘ where the volunteers are shown an initial word (’time’) and then after a short gap are shown a nonsense word (’yipt’) and a true word (’date’) at the same time and have to indicate as quickly as possible which is the real world.

The experimenters altered how related the initial word and true word were to test for the semantic distance effect, and also varied the gap between the initial word and the test to see how long the priming effect might last.

Volunteers who were under the influence of cannabis showed a definite ‘hyper-priming’ tendency where distant concepts were reacted to more quickly. Interestingly, they also showed some of this tendency when straight and sober .

Cannabis also had the effect of causing temporary psychosis-like distortions as would be expected from a psychedelic drug, but the smokers did not make more errors and were not more likely to report psychosis-like symptoms when sober, suggesting the effect was not due to general mental impairment and couldn’t be explained by underlying tendency to mental distortion.

Although the debate is not completely settled, there is now good evidence that cannabis causes a small increased risk for developing schizophrenia particularly when smokers start young. In fact, additional evidence on this front was published only this week.

The researchers discuss the possibility that long-term smokers who spend a lot of time in a chronic ‘hyper-primed’ state might make psychosis more likely by loosening the boundaries of well-grounded thought, although exactly how cannabis raises the risk of psychosis, and indeed, how exactly it affects the brain, is still not understood well-enough to make a firm judgement.

Link to PubMed entry for cannabis ‘hyper-priming’ study.

Originally posted here:
How cannabis makes thoughts tumble

Neuroskeptic covers a fascinating case of a man born with a genetic mutation meaning he had a severe lifelong deficiency of both serotonin and dopamine.

The case report concerns a gentleman with sepiapterin reductase deficiency, a genetic condition which prevents the production of the enzyme sepiapterin reductase which is essential in the synthesis of both dopamine and serotonin.

The most widely recognised symptoms of the condition, linked to the deficiency in dopamine which has an important role in controlling movement, are problems coordinating both conscious movements and the unconscious control of muscles that allows simple actions. Unconscious control requires that the brain signals one muscle to contract while releasing the complementary muscle, and problems with this process cause spasticity.

The effects the condition on serotonin, often stereotyped as the ‘happy chemical’, are less well known, but in this case it was clear that the patient wasn’t depressed but did some other difficulties:

These included increased appetite - he ate constantly, and was moderately obese - mild cognitive impairment, and disrupted sleep:

“The patient reported sleep problems since childhood. He would sleep 1 or 2 times every day since childhood and was awake during more than 2 hours most nights since adolescence. At the time of the first interview, the night sleep was irregular with a sleep onset at 22:00 and offset between 02:00 and 03:00. He often needed 1 or 2 spontaneous, long (2- to 5-h) naps during the daytime.”

After doctors did a genetic test and diagnosed SRD, they treated him with 5HTP, a precursor to serotonin. The patient’s sleep cycle immediately normalized, his appetite was reduced and his concentration and cognitive function improved (although that may have been because he was less tired)…

Overall, though, the biggest finding here was a non-finding: this patient wasn’t depressed, despite having much reduced serotonin levels. This is further evidence that serotonin isn’t the “happy chemical” in any simple sense.

This is another piece of evidence against the common myth that depression is “caused by low serotonin” although Neuroskeptic speculates whether the link between disrupted sleep and depression may indicate an effect of serotonin dysfnction.

Link to Neuroskeptic on ‘Life Without Serotonin’.
Link to summary of scientific paper.

Excerpted from:
A man with virtually no serotonin or dopamine

There are numerous forms of body distortions and out-of-body experiences reported in the neurological literature but this is the first case I’ve found of someone who experienced tics that seemed to occur in external objects.

The report was published in the journal Neurology in 1997 and concerns a man with Tourette’s syndrome, a condition of persistent tics.

These more commonly appear as almost irresistible repetitive movements that the person feels compelled to complete, but occasionally they can appear as what are known as ’sensory tics’ which are repetitive sensations such as feelings of pressure, tickle, warmth, cold, or other abnormal sensation in skin, bones, muscles, and joints.

In this case, however, the sensations felt as if they were appearing in external objects:

A 34-year-old man dated the onset of his symptoms to age 5 when he developed a compulsion to bite down on cups and glasses. The drive was so irresistible that he once shattered a glass in his mouth. He later began having painful repetitive neck extension and shoulder shrugging. During childhood, he first noticed itchy or pressure sensations, usually deep in a joint, but sometimes on the skin, in his hands, feet, and arms. The sensations eventually spread. For a period of time, the inside of his knees and ankles were particularly affected and the sensation could only be relieved by banging his ankles together. Noises including grunts, sniffs, and loud shouts began during early adolescence. A period of coprolalia was present briefly. The tics came to involve the entire body. He had associated difficulty concentrating, compulsions, and obsessions. He was given a trial of clonidine without relief. He was never tried on other medications.

The patient characterizes his motor tics as voluntary movements performed in response to the “itchy” feeling. Although he can partially suppress tics in any given location, suppression enhances the feeling that he must move another body area. He frequently has the urge to repeat what others say to him but can usually suppress it. Beginning during childhood and persisting through adulthood, the patient noticed that the itchy sensations preceding motor tics could arise in other people or in objects.

The extracorporeal sensations are associated with the need to scratch or touch the itchy item in a particular way. External sensations most frequently arise in angles, corners, and points of objects such as elbows, the edges of tables, or the edge of his computer screen. Out-of-body sensations are more likely if the patient is touching an object but can also arise without direct contact. When younger, the patient would act on the accompanying urge and would scratch his sister’s elbow. He is able to resist touching other people.

Disembodied sensations are not uncommon after neurological difficulties (for example, a recent case study of a person with epilepsy reported a feeling of complete disembodiment) and can even be induced in you and me, as the ‘rubber hand illusion‘ demonstrates.

In this case, however, it isn’t clear exactly how the Tourette’s syndrome is triggering the feeling that the sensations appear in other objects, although it does suggest that our self-other boundary is not as iron-clad as we sometimes like to believe.

Link to PubMed entry for case study.

Read the original here:
The disembodied tic