What colour is your breast-stroke? Or why synaesthesia is more about ideas than crossed-senses

People with synaesthesia experience odd sensations that make it seem as though their neural wires are crossed. A certain word might always come served with the same particular taste, or a letter or numeral might reliably evoke the same particular colour. But an emerging view among experts is that synaesthesia is grounded in concepts, not crossed senses. By this account, it's certain ideas, regardless of which sense perceives them, that trigger a particular concurrent experience. The latest evidence for this comes from Danko Nikolic and his colleagues at the Max-Planck Institute for Brain Research. They've documented two synaesthetes, HT and UJ, who experience different swimming strokes, whether performing them, watching them or merely thinking about them, as always being a certain colour.

HT and UJ, both now aged 24, began swimming competitively at an early age and the sport continues to be an important part of their lives. The first test that Nikolic's team performed was to present the pair with four black and white close-up photos of different swimming strokes and have them say which colour the strokes triggered using a book of 5500 colour shades. This was repeated four weeks later for HT and three weeks later for UJ. Three non-synaesthete control participants, all swimmers, were recruited for comparison. They similarly reported which colours the photos made them think of and they repeated the exercise after just a two-week gap.

The clear finding was that the difference from the first test to the second test in the precise colours chosen for each stroke by the synaesthetes was eight times smaller than the test-retest difference shown by the controls, thus supporting the synaesthetes' claim that different strokes always provoke the same colours.

Next the researchers administered a version of the Stroop test: the synaesthetes and controls were presented with the same swimming stroke photos as before, but this time they were shown with different coloured tones, for example in blue or yellow. The participants' task was to name the colour. If certain swimming strokes really do evoke particular colours for the synaesthetes then their colour naming ought to have been affected by the precise stroke/colour pairing on any given trial, such that you'd expect them to be quicker if the photo's colour matched the colour evoked by the stroke shown in the image. That's exactly what was found - UJ, for example, was 101ms slower when naming incongruent colours versus congruent ones. No such effect was observed for two control participants.

According to the classic view of synaesthesia as cross-wiring between senses, you'd think that swimming-style synaesthesia would require the act of swimming (via proprioception) to evoke a concurrent experience, but this study suggested it was enough to merely activate the concept of the different swim strokes by looking at pictures. This is consonant with past research showing, for example, that letter/number-colour synaesthesia can be triggered merely by imagining the necessary letter or number. Other research has documented synaeshetic experiences devoid of any particular sensory element, including so-called time-unit-space synaesthesia, in which units of time are experienced as existing in particular locations relative to the body.

"Hence, the original name of the presently investigated phenomenon syn + aesthesia (Greek for union of senses) may turn out to be misleading in respect of its true nature," the researchers said. "The term ideaesthesia (Greek for sensing concepts) may describe the phenomenon much more accurately." For more detailed discussion of how, when and why synaesthetic triggers and their concurrent experiences are acquired, it's worth checking out the full-text of the article.
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Nikolić, D., Jürgens, U., Rothen, N., Meier, B., and Mroczko, A. (2011). Swimming-style synesthesia. Cortex, 47 (7), 874-879 DOI: 10.1016/j.cortex.2011.02.008

This post was written by Christian Jarrett for the BPS Research Digest.

Stroke cures man of life-long stammer

The cerebellum is coloured green in this model

Thanks to the success of the King's Speech movie, most of us are familiar with the 'developmental' kind of stammering that begins in childhood. However, more rarely, stammering can also have a sudden onset, triggered by illness or injury to the brain. Far rarer still are cases where a person with a pre-existing, developmental stammer suffers from brain injury or disease and is subsequently cured. In fact, a team led by Magid Bakheit at Mosley Hall Hospital in Birmingham, who have newly reported such a patient, are aware of just two prior adult cases in the literature.

Bakheit's patient, a 54-year-old bilingual man, suffered a stroke that caused damage to the left side of his brain stem and both hemispheres of his cerebellum - that's the cauliflower-shaped structure, associated with motor control and other functions, which hangs off the back of the brain. The man's brain damage left him unsteady on his feet, gave him difficulty with swallowing and his speech was slightly slurred. But remarkably, his life-long stammer, characterised by repetitions of sounds, and which caused him social anxiety and avoidance, was entirely gone - an account corroborated by his wife. By the time of his discharge from hospital, the slowing of his speech was much improved and yet thankfully his stammer remained absent.

The researchers can't be sure, but they think the remission of the man's stammer is likely related to his cerebellum damage, which may have had the effect of inhibiting excessive neural activation in that structure. This would be consistent with previous research showing that people who stammer have exaggerated activation in the cerebellum compared with controls, and with the finding that successful speech therapy is associated with reductions to cerebellum activation compared with pre-treatment. A second, related possibility is that, pre-stroke, the man's cerebellum was somehow having a detrimental effect on his basal ganglia (a group of sub-cortical structures involved in motor control and other functions) and that this adverse effect was ameliorated by the stroke-induced damage. This would be consistent with reports of stammers developing in patients with diseases, such as Parkinson's, that affect the basal ganglia.

A third and final possibility, the researchers said, is simply that the slowing of the man's speech somehow aided his stammer. Indeed, reducing the rate of speech is a therapeutic approach. However, this certainly wasn't a conscious strategy employed by the patient, and as we've seen, his stammer remained in remission even as his speech rate improved.

'The complete remission of stammering following a posterior circulation stroke in our patient suggests that the cerebellum and/or its connections with brain structures has an important role in maintaining developmental stammering,' the researchers concluded.
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Bakheit AM, Frost J, and Ackroyd E (2011). Remission of life-long stammering after posterior circulation stroke. Neurocase : case studies in neuropsychology, neuropsychiatry, and behavioural neurology, 17 (1), 41-5 PMID: 20799135

The woman whose new memories are erased each night

Psychologists have documented what they believe to be a clinical first - the case of an amnesic woman whose memory for new material is erased each night that she goes to sleep (movie fans will recognise this as a plot device in the 2004 film 50 First Dates). Referred to as case FL, the woman developed these symptoms after she hit her head in a car accident in 2005, aged 48. Brain scans and neurological exams revealed no signs of brain damage, thus suggesting the woman is exhibiting what's known as psychogenic or functional amnesia - that is, symptoms in the absence of any detectable organic cause.

FL claims that on any given day her memory for newly acquired material is fine until she has a night's sleep, during which the new memories are erased (unlike standard cases of psychogenic amnesia, she says her memories from before her accident are preserved). FL's performance on lab-based memory tests was largely in keeping with her claims, with one key exception. Christine Smith and her team deployed some trickery, intermingling test items (scenes) from earlier in the day with items from previous days. FL's memory for items that she thought were from earlier in the day, but were actually seen on earlier days, was intact and comparable to the memory performance of healthy controls.

So was FL faking it, perhaps in pursuit of a compensation claim? Smith's team don't think so. Although healthy controls who were asked to fake FL's symptoms performed similarly on the memory tests, there were also differences. For example, unlike the healthy fakers, FL showed deficits in motor learning, and her confidence for test items dropped with repeated testing whereas theirs increased.

The researchers' theory is that FL truly believes she has the memory deficit that she describes and that unconscious processes may be involved in its manifestation. FL denied having seen the film 50 First Dates, which was released a year before her accident. However, she admitted that the film's female lead, Drew Barrymore, was her favourite actress, so she may have been aware of its plot. The film 'may have influenced FL's concept of how memory could fail after a car accident', the researchers said. 'The brain uses preexisting concepts of memory and through altered brain function creates a particular constellation of symptoms.'

What about treatment? Reassuring FL that evidence had been found for the intact functioning of her overnight memory proved unsuccessful. What did work was testing the limits of FL's memory-washing system. Thirty-six hours without sleep and her memories were okay. An hour's nap during the day and they were okay. In the end, it was established that FL can sleep at night for up to four to six hours at a time without experiencing the sense that she's lost the day's memories. By setting an alarm each night to wake her after bouts of three and a half hours sleep, FL has managed to overcome her strange condition. 'At our most recent contact (March 2010), she and her husband reported that she continues to use this regimen successfully,' the researchers said.
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Smith, C., Frascino, J., Kripke, D., McHugh, P., Treisman, G., & Squire, L. (2010). Losing memories overnight: A unique form of human amnesia. Neuropsychologia, 48 (10), 2833-2840 DOI: 10.1016/j.neuropsychologia.2010.05.025

Further reading: Amnesia at the movies.