In brief...
In general, the types of synesthesia with a non-visual concurrent (olfactory, gustatory, tactile, etc.) are much less common than those with a concurrent of colour.
No specific type/subtype/manifestation of synesthesia can be called “the
rarest type” because there are so
many that only a few people have (and it’s impossible to calculate exactly how
many people have them), and there are also types that logically exist but have
never been reported by anyone.
Also, there is no universal system for determining what actually constitutes “a type of synesthesia”.
What are some candidates for the rarest type?
Here are some types or sub-types
that are very uncommon (with links to the page containing information on them
and reports by people who have them):
Grapheme-smell/taste (each letter
and/or number has a smell or taste. This type shouldn’t be confused with
lexical-gustatory synesthesia, which is word-taste and is much more common as probably
around 3% or more of synesthetes have it. Lexical-olfactory,
where words have smells, is rarer than lexical-gustatory.)
Tactile-olfactory and
tactile-gustatory (on touching different surfaces, the synesthete consistently
perceives a particular smell or taste)
Perceived emotion-touch sensations
(the perception of different emotions in other people creates a specific,
consistent tactile sensation in a particular part of the body)
Conceptual-auditory synesthesia is a very uncommon type, and an excellent example of a very rare or perhaps unique manifestation is hairstyles-sound.
However, we cannot really say that
the above types of synesthesia are the least common, as cases have been
described and confirmed.
The ones that really would be the rarest are those
for which no case has ever been reported. Some
examples of types that probably exist but which as far as I know no-one has reported yet are:
Kinetics-smell and kinetics-taste
(different movements of one’s own body create the consistent perception of a
smell or taste)
Grapheme-tactile (the concept of each letter or number produces
a specific, consistent tactile sensation in a particular part of the body)
A problem with calculating the
rarest types: the sample size
It is difficult to estimate the
frequency of the most uncommon types of synesthesia because not enough people
have them to provide a sufficiently sized sample population for testing. Quite
reliable prevalence figures exist for the more common types of synesthesia,
because rigorous scientific methods have been used to assess many hundreds of
people after verifying the genuineness of their synesthetic experiences using
techniques such as the Battery Test. But for
the more uncommon types the reliable samples are very small, and in the case of
the very rare types they are practically zero and there are simply no figures
available: all we can do is guess.
But what does a “type of
synesthesia” consist of anyway?
One of the problems in attempting
to define what the rarest synesthesia types might be is in classifying what
actually constitutes a “type of synesthesia”: how should we subdivide? Breaking
them down into main groups – auditory-visual, olfactory-tactile, and so on – is
not the same as finely subdividing them by particular manifestations into types
like “decades-to-colour”, “weekday personification”, “morpheme-colour” or
“novels I’ve read-spatial location”.
If we subdivide by overarching groups, the most common synesthesias would be those that have a colour perception as their concurrent, and the least common would probably be those with a tactile or olfactory/gustatory concurrent (see footnote 2).
A large-scale research study by Novich, Cheng and Eagleman, Is synaesthesia one condition or many? A large-scale analysis reveals subgroups (2011) proposed 5 clusters of synesthesia types:
- coloured sequences (month-colour, grapheme-colour, etc.)- coloured sensations (pain-colour, for example)
- music-colour
- synesthesias with non-visual concurrents (evoking smell, sound, touch, taste, etc.)
- spatial sequences
The least common cluster would be non-visual concurrents. Talking
about clusters rather than specific types, subtypes or manifestations of
synesthesia is a much more practical way of trying to determine what might be
the “least common synesthesia type”.
On this page of the Tree: List of types of synesthesia by prevalence, the furthest column to the right shows a list of the types and manifestations of synesthesia that could be the rarest, with an incidence of less than 1% among the synesthete population. As you can see, they are very numerous: much more numerous than the more common types. I’d also like to clarify that this is only a rough approximation to the real situation, as apart from there being no reliable figures available for these types some of them might also be more widespread than was formerly believed (and they might jump to a higher column when more cases are reported).
Weak synesthesias
It should be borne in mind that
many synesthetes have only very mild manifestations of a particular type of
synesthesia or have simply not focused on it enough to realise that they have
it, and this also influences the number of reports and figures available to
researchers. In the past, as a result of this effect and the fact that
synesthesia was hardly talked about (and up to about 1990 or 2000 scientific
knowledge on the subject was much more limited), it was generally believed to
be an extremely rare phenomenon, although it is now known that this is not the
case, with a commonly accepted figure of almost 4% of synesthetes in the
population. When a type of synesthesia begins
to be discussed, it is commented in the dedicated groups and forums in the
social networks and more people appear who can talk about their own experiences
with it. But the rarer types of synesthesia
are less talked about, precisely because they are rarer… and logically it is
more difficult for them to come to light than in the case of more common types.
Synesthetic concurrents: mixed or
on the rocks?
Another effect that complicates the
possibility of counting cases of certain types of synesthesia is that some
concurrents tend to occur jointly with others, making them more difficult to
classify. Grapheme-temperature synesthesia is an example of this: for
many synesthetes, temperature is probably an integral part of their grapheme-colour
synesthesia, but it wouldn’t occur to them to say that they have
grapheme-temperature synesthesia. If we only
count the people who experience a temperature concurrent without an associated
colour perception we would have one figure, while if we counted all
grapheme-colour synesthetes with this additional temperature perception we
would have another, much higher, one. Which
would be correct?
Who has the rarest forms of
synesthesia?
Whatever the case, it is
interesting to note that the most uncommon types of synesthesia tend to be
experienced by people with a very high “synesthetic disposition”. This
means that they have many different types, often strongly expressed. This phenomenon tends to occur more frequently in people on
the autism spectrum, although not exclusively so. If someone has only one subtype or manifestation of
synesthesia, or very few, it is very unlikely that this type would be precisely
one of the rarest. If that seems to be the
case, the phenomenon they are experiencing is probably not a type of
synesthesia.
This page last updated: 16 May 2023
Post published: 13 July 2022
This page is about: There isn’t a rarest type of synesthesia What is the rarest type of synaesthesia? What is the rarest form of synesthesia? What is the rarest form of synaesthesia?
"No specific type/subtype/manifestation of synesthesia can be called “the rarest type” because there are so many that only a few people have (and it’s impossible to calculate exactly how many people have them), and there are also types that logically exist but have never been reported by anyone."
ReplyDeleteThis is a wow and mindblowing moment.
Especially the "logical types which exist but were never reported'.
1 person finds another and they find another.
Adelaide
Thank you for your comments!
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