It is hard to imagine that reality could be anything other than what we see around us. The sights, sounds, tastes and smells we experience every day feel fixed and permanent, as if anybody else standing in our shoes would see the same colours, hear the same sounds, taste the same flavours, and so on. Our sensations feel unambiguous: red is red, onions taste of onion, and the sound of a piano is, well, just that. But as a neuropsychologist, I know that our perception of the world is filtered through the individuality of our brain. And because some brains differ in subtle ways, some people experience the world as a radically different place. Nowhere is this more obvious than in the experiences of people with synaesthesia.
Synaesthesia is an inherited condition that gives rise to a 'merging of the senses'. For those who experience it—people known as synaesthetes—everyday activities such as reading or listening to music trigger extraordinary impressions of colours, tastes, smells, touch and other sensations. Imagine a world where the senses are inexplicably combined. A piano note might be a deep crimson red, the word ‘society’ might taste of fried chicken. Simply eating chocolate could produce clouds of purple haze in your visual field or a spiky feeling against your hand. All these sensations are caused by differences in the wiring of synaesthetes’ brains, which allow one part to become active when another part is stimulated. In extreme cases, every taste, every colour, every sound and smell could combine to produce a kaleidoscope of sensation, which the synaesthete carries around during every waking hour.
Recently, we have uncovered information about a range of synaesthesias, from the types of cross-sensation described above to more abstract experiences. Some synaesthetes ‘see’ time mapped out in space; they can point to August, say, on their left, or the year 2009 somewhere on their right. (Ask around . . . it’s more common than you’d think.) Again, these sensations are the result of benign extra brain connections, and research shows this can come with advantages. We know that synaesthetes tend to be more creative, some have better memories, and our recent paper in the journal Cortex has linked synaesthesia to savantism. Savants are genius-like individuals who have phenomenal skills combined with developmental disorders such as autism. Some savants are ‘human calculators’; some can recall pi to 22,000 decimal places; others can tell you exactly what they were doing during any moment in their entire life: ask them what they were wearing on Tuesday, July 20th, 1971, and they will tell you immediately. Together with colleagues in Edinburgh, London and Cambridge, my research suggests that savants are often able to achieve these phenomenal feats because they coincidentally have both autism, which gives them an obsessive focus, and synaesthesia, which gives them extra ways to remember information. Ask the savant Daniel Tammet how he recalls his many thousand digits of pi, and he will tell you that he uses his synaesthesia; for him every digit has a colour, texture, size and shape, and these create a colourful ‘number landscape’ which he mentally scans to read back the digits. In a similar way, we’ve shown that savants with extraordinary memories for past events are likely to be reading these off their synaesthetic ‘time-lines’.
Although the experiences of synaesthetes seem highly unusual to the average person, an understanding of the human brain makes these experiences seem reasonable, and even expected. Consider a synaesthete who ‘sees’ a piano note as red. For the average person, the colour red is only red because certain neurons fire in our occipital lobe, the vision centre of the brain. But if those same neurons fired for any other reason, we would see red where it simply doesn’t exist. Cue the experiences of synaesthetes—but this can also be true for the average person. The Canadian neurosurgeon Wilder Penfield used pioneering procedures in the mid-20th century that placed electrodes directly onto the human brain during surgery while the patient was still awake. Patients reported vivid impressions of colours, smells, shapes, etc., a powerful indication that subtle brain activity can trigger extraordinary sensations, even without any direct correspondence in the outside world.
My own knowledge of true synaesthesia comes from the many hundreds of synaesthetes who’ve been kind enough to share their experiences with me, but what I’ll never have is first-hand knowledge of how these experiences feel. But this cuts both ways: when I tell synaesthetes I don’t have colourful letters or tasty words, they reply with a smile and a slight sense of disbelief. Perhaps it is this difference in consciousness that will always intrigue us about the experiences of those in the other camp. The best we can do is to acknowledge that the outside world comes to us not as a fixed commodity, but as a fluid message to be interpreted by our own individual minds.