What is synaesthesia?

Mathieu Ranger
23 January 2012

If you think these questions are a little bit silly, then your brain is functioning normally. If, on the other hand, you have an answer to some or all of these questions then you’re likely afflicted with a neurological condition called “synaesthesia”.

Say what!?

OK, please don’t panic. Synaesthesia is in no way dangerous and, in fact, synaesthetes — people with synaesthesia — often perceive their condition as a positive thing.

Fast Fact: Synaesthesia is much more common among poets, artists and novelists than in the general population.

Synaesthesia is a condition in which the stimulation of one sense or cognitive pathway involuntarily leads to the stimulation of another unrelated sense or cognitive pathway.


Well, for some synaesthetes, that can mean that when a C-sharp note is heard, they sense the taste of chocolate. For other synaesthetes, the letters of the alphabet or days of the week may seem to have a colour. Some synaesthetes might also “see” time as having specific locations relative to their bodies. For example, they perceive the year 1994 as being literally “behind them”.

Fast Fact: Most people with synaesthesia are “associators” (e.g. think a letter is blue when it looks black). Others are “projectors” - they actually see the letter as being coloured blue.

So what’s behind synaesthesia? While no one quite knows what causes synaesthesia, the current prevailing idea is that it’s caused by a failure of the early developing brain to properly sever the connections between areas responsible for different perceptions. As a result, synaesthetes “see smells”, and “taste colours", among other things. Interestingly enough, synaesthesia tends to run in families, meaning that it’s probably caused by a mutation in some gene and that if you have it, you’re likely to find another family member that also has it.

Fast Fact: More than 60 types of synaesthesia have been reported!

One final thing. A big question that some of you newly-discovered synaesthetes might have is, “Doesn’t everybody think like this?” The answer is no, but because it’s not easy to test for synaesthesia, it’s difficult to determine how many people have this condition. Estimations as to the prevalence of synaesthesia range from one in 25,000 to one in 20. It’s more likely that the number falls somewhere in between.

Learn More!

To see a list of all the different types of synaesthesia that have been identified, click here.

The names for the various types of synaesthesia can help you understand what they are. The left part of the name indicates the trigger of the synaesthetic experience (e.g. sound) while the right part of the name indicates which totally unrelated sense or cognitive pathway is activated by the trigger (e.g. smell).

Article first published on December 29, 2010.

Mathieu Ranger

I am a graduate student in the Department of Molecular Genetics at the University of Toronto. By day I study yeast and by night...well I don't. I have joined CurioCity to put my communication skills to the test. Let's see how I do!

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