The Smell of Green Thunder: How Does Synesthesia Differ from Hallucination? World Science Festival. November 2012.
What's the difference between synaesthesia and hallucination? The celebrity neurologist and best-selling author Dr Oliver Sacks explains in a short video. The differences are very easy to grasp - natural synesthesia is inborn, and pretty-much permanent and stable, while pathological or drug-induced forms of synaesthesia and hallucinations are not. Natural synaesthesia is stable in that the same associations hold, such as between a particular conceptual, motor or sensory trigger and a particular anomalous sensory or conceptual effect or experience. The bass guitar in a particular rock song will always trigger the experience of a very specific shade of teal, or the concept of the number 21 will always be associated with a particular personification that has a particular age, gender and personality traits.
Would I be right in stating that Jani Schofield's "hallucinations" are inborn, permanent and stable like synaesthesia? I'm not sure that anyone has bothered to check whether there are stable associations in Jani's reported experiences, but it's pretty clear that her distinctive way of thinking is inborn and permanent, like synaesthesia and unlike the vast majority of cases of schizophrenia. What is clear in Jani's case is that the alternative world that she experiences, which is held up repeatedly in media reports about Jani as evidence of florid hallucinatory schizophrenia, is in fact a world of imaginary friends which seems to have many characteristics in common with synaesthesia. As far as I know, at no time in the history of psychiatry has there been any theoretical confusion between the different phenomena of psychotic hallucination and childhood imaginary friends. To identify a child who has imaginary friends as a child displaying psychosis seems to me to be the stupidest, grossest clinical blunder, and to completely ignore the many obvious hints that synaesthesia is also an important element in Jani's psychology seems to me like inexcusable ignorance or deliberate omission.
I've got a few gripes and reservations about the video linked to below, but I think the main message is basically sound. The observations about synaesthesia by Dr Sacks need to considered in the light of the fact that he is not a synaesthete and thus has no first-hand understanding of the phenomenon. I object to the fallacy of forced choice in the summary about the video - "is synaesthesia hallucination or is it real?" I'm not sure whether this question is just plain stupid or is based on a questionable assumption about sensory experiences. In what sense are any of the sensory experiences of a non-synaesthete real? Are your ideas or experiences real? Being a synaesthete who knows that she is a synaesthete, I understand that many of my experiences are atypical, and some make no logical sense, but does that make them less real? Many non-synaesthetes identify an association between the word "bouba" and a shape that is rounded and lumpy, but is there any real link there, between a nonsensical word and a shape? Questions about what is real and what is not real are for philosophers to have a tug over. Can you be bothered?
One most disappointing aspect of the video was that the lady who posed the quite good question to Dr Sacks was informed and inspired by the first book written by Daniel Tammet, who claimed to have an extraordinary case of synaesthesia, among many other extraordinary claims. Sigh. It appears that the lady in the video is a synaesthete, but she observed that her synaesthesia is not as "dramatic" as other people's accounts of synaesthesia. Indeed. I've never seen or heard of any synaesthete claiming to have synaesthesia quite like Tammet's, with his coloured abstract mental landscapes that somehow encode long numbers and synaesthetic photisms that automatically reveal the solutions to difficult mental calculations. His synaesthesia is about as atypical as Jani's schizophrenia, which should make anyone wonder....