For most of us, sound is something pretty unremarkable. In our daily lives, we are overwhelmed with sounds, for example the whirr of a blender or a Top 40 song. While we might look forward to the smoothie or appreciate the music, that’s pretty much it. But, this is not the case for everyone.

For the 4 percent of the population who experience synaesthesia, those sounds, among others, are also experienced through other senses too. That blender whirr might be buttercup yellow and Taylor Swift’s latest song could be the prickle of Velcro, punctuated by the tickle of a feather.

This may sound fanciful, but it’s a real phenomenon! It also highlights how interesting our hearing, senses and human brains are. So let’s give synaesthesia a closer look – and a closer smell, taste, touch and listen too.

Let’s start by unpacking the word. Synaesthesia literally means ‘feeling together’, and synaesthetes are individuals whose five senses, somehow, are cross-wired. This jumbling can happen in many different ways. Most commonly, letters – or ‘graphemes’ – are felt as colours, but sometimes sounds have distinct personalities and genders. Time might be muddled with flavour. Even emotions can register as particular odours. Over 80 varieties of synaesthesia have been described by researchers – and as wacky as it all sounds, scientific studies have backed this up.

Even as recently as the 1980s, scientists regarded those who claimed to experience synaesthesia as either hallucinating, crazy or simply seeking attention. At the time, scientific wisdom dictated that the five senses travel along five distinct and separate pathways in the brain. But since then, neuroimaging has shown that the brain works in a far more mysterious way than that.

In synaesthetes, different areas of the cortex activate in response to sensory stimulus, giving a scientific explanation for why numbers may register as musical notes or why days of the week may have a flavour. Other studies have shown that hearing and touch can be readily mixed up by the brain and that certain kinds of stroke can induce synaesthesia even in individuals who have never experienced it previously.

So what’s synaesthesia like from the inside? To quote the writer and translator Daniel Tammet, "my worlds of words and numbers blur with colour, emotion, and personality." Scientific papers document synaesthetic experience in vivid detail – like the sound of a high C on a trumpet creating a flash of fire-engine red.

In fact, chances are you’ve come into contact with a synaesthetic work of art, literature, or music already. More and more studies show that the condition is most common among creative types. Kanye, Beyoncé, and Lady Gaga reportedly have synaesthesia. In the world of visual arts, Kandinsky and David Hockney are documented synaesthetes.

The novelist, Vladimir Nabokov, wrote extensively about his tendency to feel letters and words in colour. No doubt the creative fields are full of synaesthetes because the condition confers a real artistic advantage. With a greater aesthetic sensitivity than most people, these individuals are naturally attracted to fields where they can put their heightened senses to use.

If reading this induces a flash (maybe a brilliant blue one) of recognition, there’s probably a good reason. As weird as it sounds, synaesthesia is not as rare as we once thought. While the estimated rate is 1 in 2000 people, the chances increase if you’re female (75% of synaesthetes) and increase again if you’re left-handed.

There’s also a known genetic link for the most common form of ‘grapheme-colour synaesthesia’, where, for example, the letter A may be red, L may be green, and S may be pink. If your parents or siblings experience this, there’s a higher chance you will too. In fact, many individuals who have synaesthesia may never have realised that the way they perceive the world is different from the norm. They may have assumed that every dog bark is scratchy or every January is lemon curd. Who’s to say they’re wrong?

All of this tells us something pretty interesting about our senses, hearing included. The way our brains operate is far stranger than we have previously thought – less linear, more idiosyncratic – and perception isn’t simply a matter of stimulus in, experience out.

As Daniel Tammet explains, "the world is richer, vaster than it too often seems to be" – even if you’re not a synaesthete. What we hear and what we perceive comes as much from our brain as from our ears, and that’s a pretty cool thing from any perspective – blue, spiky, frangipani-scented or not.