Recently a study was published that investigated the relationship between synaesthetic experiences and coupled resting state networks that could be measured via FMRI.

http://www.jneurosci.org/content/32/22/7614.abstract

http://idw-online.de/pages/de/news480257

Other:

http://www.newscientist.com/article/dn21183-hyperactive-neurons-build-brains-in-synaesthesia.html

http://medicalxpress.com/news/2011-11-synaesthesia-linked-hyper-excitable-brain.html

http://medicalxpress.com/news/2011-11-synesthesia-survived-evolution.html

http://www.pnas.org/content/108/51/20661

Regards,

Joachim

David Eagleman developed a battery to test for a number of different types of synesthesia based on repetition of association over time (synesthetes are more consistent in their sensory associations than non-synesthetes). http://synesthete.org/

However, this test should only be considered reliable for certain types of visual/auditory/lexical synesthesia.

Until fMRI becomes an available and reliable tool for identifying synesthesia, Eagleman's battery is worth checking out for those types of synesthesia. Otherwise, self report remains the best method of identification.

I am both a (congenital) synesthete and have been a researcher of synesthesia for over 30 years. I have interacted with easily over 3000 synesthetes in my lifetime. At a recent conference on “Synesthesia and Children”, held in Ulm, Germany, this last May, this question regarding identifying synesthete children came up.

My experience has been that, over the last 30 years, I have developed a bit of a talent for identifying certain types of synesthesia – mainly those more common types having to do with music, graphemes, or time units. But that’s not really saying much.

My experience is also that we tend to really over-complicate this whole matter, when, in many ways, it can be quite simple:

Now, if we ask a 10-year-old child, “What color is the letter ‘A’?” – Well, that won’t work, because we would be implying that the letter ‘A’ does indeed (or at least might) have a color. And also setting up situations such that the child is more likely to answer with a base color term (e.g., “red”, or “green”) than a more elaborate description (e.g., “dusky pastel lavender”).

But, on the other hand, if you ask a child (or adult) to “Describe the number 5.” – That is open-ended, without any implications of 5 having any synesthetic qualities. And then you just wait and notice whether anybody describes 5 as, say, red, or mean, or male.

Likewise, note the difference between asking “What color does a piano make?”, and asking someone to “Describe the sound of a piano.” Or “Describe the experience of eating an orange.” Or the difference between, “What color is Monday/September?” and “Describe Monday/September?”

Likewise, play about ten notes on a musical instrument, and then ask someone to “Describe the music I just played.”

Sean A. Day, President, American Synesthesia Association

I agree with Sean - just ask them! At the end of the day, it's a subjective phenomenon - there is no definitive test (fMRI or psychophysical) to identify synaesthetes definitively. If a person does not report any type of synaesthetic experience then they are most likely not a synaesthete (though you have to know the right questions to ask as some people don't know that they are or that the way they perceive things is any different from anyone else).

Also, I should say, once you start asking people you will find that it is quite a common condition - estimates vary, but probably 2-4%.

Beyond that, there actually is some sense in addressing whether or not one has synesthesia like addressing whether or not one has a headache.

If you ask me whether or not I have a headache, I will probably tell you what my current situation is, and probably will not lie. Yes, people can and do indeed lie about having a headache. But, in dealing with someone, you can usually tell pretty quickly if he or she is lying or not.

But, if we want to use our fMRIs, ERGs or other scanning mechanisms to search for my headache – what exactly are we going to search for? As we keep in mind that there are many, many causes to headaches: I could have a low level of blood sugar, or a high level of stress, or a hormonal imbalance, or a bullet imbedded inside my skull, or a developing tumor, or an angry neighbor who just socked me in the nose.

And we find ourselves back to regurgitating the old “correlation does not equal causation” phrase: We can run our grapheme-to-color synesthetes through our fMRIs, and watch V4/V8 light up atypically. This tells us that V4/V8 lights up atypically; it doesn’t tell us why, or what all else (e.g., genetics, hormones, history of drug abuse) is involved.

I find I have developed a reputation for being an annoying pest, because I keep on reminding synesthesia researchers that, with over 65 different types of synesthesia out there, it is, simply put, drastically unwise to over-generalize things – such as causation – about synesthesiae. Note that we don’t do that when we talk about headaches or cancers.

Many synaesthetes are unaware that most other people do not experience the same associations that they do, so they regard themselves as 'normal' and do not answer 'Yes' to a questionnaire that implies the opposite. Also, most associations are highly idiosynchratic, so even if the questionnaire gives examples (e.g., a particular color-sound or grapheme-color association), a person with a different form of association (say, touch-taste) may not self-identify as a synaesthete -- their particular association seems to them to be too far removed from the examples. As a result, I think some types of synaesthesia may be undercounted by questionnaires, even if face-to-face interactions soon reveal the condition. I'd be interested to know if others agree. (Note: I entirely agree with Sean Day about the role of scanning).

Thank you for all Replies. How does one select the sample? Is there any recommended sampling technique?

Adam Reeves: yes, that has been my experience. Many types under-recognised, sometimes even by people who have heard of synaesthesia but think it is something else (like coloured letters or music only). I have spoken with people who have coloured smell or who see the words when people are talking who were not aware that that was synaesthesia. Also, as you say, many who don't know that not everyone thinks of numbers when they see particular shapes (like a door handle) or don't realise not everyone has a number form. It's almost impossible to cover all these types in a questionnaire - there's no substitute for a direct conversation.

Thank you for all replies.I identified different types of synesthesia people by using online questionnaires developed by David Eagleman,personification of numbers by Noam Sagiv. and also self reports.

Sean,

Your experience may help me to identify a possible type of synesthetia..

I am an avid crossword solver and I have a certain talent for language - my degree is in literature and philosophy and I am a published poet. I noticed a phenomenon recently that might possibly be a  very common form of synesthesia.

Many people have had the peculiar experience of being certain that they know someone's name but, at the same time, being completely unable to retrieve it. Like many other people, when this sort of thing occurs, I adopt the strategy of going through the alphabet to see which letters my mind 9or subconscious) 'flags' as being likely components of the person's name. I had previously assumed that I was always searching for the first letters of their name. However, I noticed recently that this is not the case. It seems that, for me at least, it does not matter where the letter occurs in the name at all!

After closely observing the phenomenon I came to the conclusion that this strategy is not a logical process but seems to depend upon a unique type of subtle experience. It is almost as if the mind is able to identify those letters that belong in the person's name by their introspective feel - like a smell or a taste - but neither of these - something else!!!

From this we may speculate of the relation between language and synesthesia. When we learn nouns and proper names do the letters and the sounds of  words assume assume unique set of relations independent of their place within the logical structure of language. Do letters (and the sound of letters) have a different significance for us as individuals depending upon what we are thinking about?

Any thoughts?

Sean Day and Brady Berman: I am a synaesthete: colours with days, months and music. I am looking at colour-music synaesthesia for my Masters dissertation and I've just tried the Eagleman test myself to see if it would be useful for my study. It was fine for the days and months and I came out with a result I expected, but the music one was no good for me. It tested chords and notes in isolation. I get colours whist listening to certain pieces of music. Not for every piece either. The music will have an overall 'hue' rather than a colour in particular. God knows how you could measure that!  Synaesthesia is so individualised and subjective.  Direct conversation ie qualitative research, would seem to be the better way to assess colour-music perhaps? Any other ideas? 

 Caroline Curwen's answer brings out a distinction, one that might be useful, between concrete and particular, inducer-inducee pairs (letter P is blue) versus abstract (non-specific), categorical pairs (Schubert is swimmy).

 Both are reproducible, as letter P is always blue when it is the first letter of a word, and Schubert is always swimmy went heard in a particular mood,  but one cannot take the concrete case as illustrative of the abstract one, since reproducible particulars are not reproducible categories. By 'category', I mean a broadly-defined collection of sensory impressions or states.

 Davia's case, as described, is associative, but not synaesthetic, as the definition implies a sensory experience of some kind, even if it is non-specific.

**

 Sean: I worry that asking someone to 'describe' something is not enough. If I ask someone to describe June, he or she could say all sorts of things about Summertime without thinking that I was fishing for an answer about what type of sensation is induced. So the percentage of synaesthetes would be underestimated by this procedure.  On the good side: those who were so identified, would likely be true synaesthetes.

 Instead, I would be up front, and explain that sometimes letters and words (if these are the focus of the study) have associated sounds, colors, shapes, or other feels, and ask the person if they have any experience of this.  Older children, like adults, will anyway want to know 'what one is getting at'.