Sensory Fluidity

What do you think it’d be like to see a smell? Or to feel an electromagnetic field?

Brueghel liked to get all allegorical with the senses.

In the last few posts, I’ve talked a lot about the differences between the synthesized concept of a self, and the raw subjective experience of being oneself in the present moment. I’ve also explored some of the boundaries and dimensions of selfhood. But this all leaves a question that’s nagged at my mind for years: what exactly is subjective experience?

It’s simple enough to say that my perceptions of reality (both external and internal) are represented by coordinated patterns of activity in my nervous system – but that doesn’t really answer the question: what do I really mean when I say I “experience” those patterns? What are the precise neurophysiological correlates of “having an experience?”

In a recent blog post, Bradley Voytek expresses this in a way I can really relate to:

When we “hear” things, the sound pressure waveform hits the tympanic membrane (eardrum) and ultimately causes the basilar membrane in your cochlea to vibrate. The basilar membrane is stiffer at one end (the basal end) and less stiff at the other end (the apical end). Okay, great, so we know a ton of the basic biology and cellular mechanisms of the signal transduction mechanisms of our sensory apparatus. But damn if I’m still not amazed by the actual experience of sensation.

I’ve got to admit, the nature of that actual experience has me a bit stumped at the moment. But thinking about it has raised some intriguing considerations that I think are worth mulling over. Here’s the thing: the senses we use to experience the world aren’t as hard-wired or discrete as we often assume.

One common example is synesthesia – a condition in which stimulation of one sensory or cognitive pathway leads to activation of another. In one patient’s case, sounds triggered a somatosensory response:

About a year and a half after her stroke, a 36-year-old professor started to feel sounds. A radio announcer’s voice made her tingle. Background noise in a plane felt physically uncomfortable. Sophisticated imaging of the woman’s brain revealed that new links had grown between its auditory part, which processes sound, and the somatosensory region, which handles touch.

This has led some scientists to research the idea that our sense of hearing developed as an enhancement as our sense of touch – a hypothesis supported by lab tests in which patients are better able to detect a quiet sound when their skin’s touch receptors are stimulated, and vice versa.

Then there are cases of blind patients who use echolocation to navigate. Scientists have found that most sounds these patients hear are processed in their auditory cortex – but sounds used for echolocation are processed in the visual cortex, allowing these patients to literally see an image of their environment constructed from sound. One guy has even learned to beat video games from sound cues alone.

Quinn Norton's finger, displaying Magneto-style powers.

And some people have gone so far as to forcibly hack their own senses. Quinn Norton, for example, inserted a magnet into her hand, and discovered it enabled her to feel electromagnetic fields. According to Norton and other body hackers, projects like these are just the beginning – we may be the first generation to choose what senses we have, and how we want to experience them.

So, while it might be tricky to pin down just what subjective experience is, it’s clear that the senses from which it’s constructed are incredibly flexible and fluid. And as Voytek is quick to point out, the amount of our sensory experience that we consciously pay attention to is just a fraction of what we actually receive:

It turns out that humans can, in fact, detect as few as 2 photons entering the retina. Similarly, it appears that the limits to our threshold of hearing may actually be Brownian motion. That means that we can almost hear the random movements of atoms. We can also smell as few as 30 molecules of certain substances.

But our brains – at least, our conscious attention – can’t parse all this data at every moment of the day. The visual pathway is a good example: our pupils can contract or expand in response to overall light levels, our retinas have a built-in response threshold that prevents them from passing along every bit of input they receive, and the visual cortex devotes most of its resources to analyzing motion and edges, while filling in the more monotonous areas (hence, why we usually don’t notice our blind spots). In other words, the entire nervous system is adept at filtering out all but the most unusual data.

One funny example of this is the classic “selective attention test” video. Take a minute to watch it, and see if you can catch the unusual element. As Voytek says, “How can we see two photons, but miss that?!” Because attention is a limited resource.

Still, as the examples above demonstrate, the human connectome is stunningly pliable, and can learn to rewire its sensory perceptions – or even to perceive entirely new senses – with a bit of practice.

I think it could be fun to write some tutorials on attention hacking, and explore some ways in which we could all push our own senses to new heights of perceptive sensitivity and fluidity. I’d say this holds some intriguing implications for erotic neurophysiology – but I think that’s only the beginning. As Voytek says, we may all be “inattentive superheroes” just waiting to be born.

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