Body & Self · about 4 minutes
The Heartbeat You Can't Hear
There is a fist-sized muscle in your chest that has contracted something like three billion times without ever once asking your permission, and it is doing it right now, about an arm's length below the thing reading this sentence.
Quick question, then. How many times has it beaten since you started this paragraph?
Before we start. This exhibit asks you to pay close attention to your own heartbeat and then to take your pulse. For most people that is merely interesting. If you live with health anxiety or a cardiac condition, attending to your heartbeat can be genuinely unpleasant -- and there is good evidence it raises anxiety in exactly the people it bothers. Skip straight to the explanation if you'd rather; the room makes complete sense without doing it, and nothing below is a test you can fail.
Two parts. First you count, using nothing but whatever you can feel from the inside. Then you find out what actually happened.
Part one · silent counting
Sit still. Do not take your pulse -- no fingers on the wrist, none on the neck. Count only the beats you can actually feel from inside your own body. We will tell you when to stop.
Counting. Keep going until we say stop -- and no, we're not showing you the clock. That is on purpose, and we'll explain why afterwards.
Stop. How many beats did you feel?
Now find your pulse -- two fingers on the inside of your wrist, below the thumb, or gently on the side of your neck. Take your time. When you have it, press the circle once per beat and keep going until we say stop.
0
No problem -- plenty of people can't, and it isn't a character flaw. If you happen to know your resting heart rate, put it in and we'll do the arithmetic. Otherwise go straight on.
Your numbers
One trial, one person, one museum. This is a demonstration, not a measurement -- the real version runs several intervals with a proper heart-rate monitor, and even then there is an argument about what it means, which is coming up.
The sense you never got told about
The five senses point outward. There is a sixth system pointing the other way -- inward, at your own machinery -- and almost nobody is taught its name. Interoception is the sense of your own body's internal state: heartbeat, breath, gut, temperature, blood chemistry, the specific and unglamorous news that you need a wee.
It runs mostly without you. A dedicated pathway carries it up the spinal cord and into the insula, a fold of cortex tucked deep in the side of your brain, which appears to assemble all of it into something like a running summary of how the body is doing. You are not usually conscious of the summary. You are, arguably, conscious from it.
And the interesting part is how much people differ. Some people track their own heartbeat well. Many are wildly off. The usual direction of the error is undercounting -- as a population we lowball our own resting heart rate by around seven beats a minute -- but individuals range enormously in both directions, and there is no obvious way to tell from the outside which sort of person you are talking to.
Why anyone cares: the body might be where feelings start
In 1884 William James asked a question that still hasn't been settled. Do you run from the bear because you are afraid -- or are you afraid because you notice yourself running? His answer was the second one: the emotion, he said, is the perception of the bodily change. Racing heart, cold hands, tight chest, and then, downstream of all that, fear.
If James was even partly right, then reading your own body is not a party trick -- it is the raw material of your emotional life, and people who read it better should have a different relationship with their feelings. That is a testable claim, and it is roughly what interoception research has spent forty years chasing: links to anxiety, to emotional granularity (whether you feel "bad" or specifically feel "resentful"), to alexithymia, to how well therapy works.
Two rooms from here the same idea appears wearing different clothes. The arousal dial in Exhibit № 37 -- the one that separates rage from despair -- is, in the end, a number about your body. You have just tried to read that dial directly, off the original instrument.
Now the awkward part
Everything above is built on a task very much like the one you just did: count your heartbeats, compare with the truth, call the difference interoceptive accuracy. It has been the field's workhorse since Rainer Schandry introduced it in 1981. And there is a serious, well-evidenced case that it does not measure what its name says.
The problem is that there are two completely different ways to be good at it. You can feel your heartbeats. Or you can know roughly what your resting heart rate is and quietly do arithmetic. Both produce a good score, and the number alone cannot tell them apart.
The evidence is not subtle. When people's counts are compared with both their actual heart rate and their beliefs about their heart rate, the counts track the beliefs more closely than the heart. Give people accurate feedback about their rate and their scores improve -- but give them false feedback and their scores improve too, which is a devastating little result: what improved was the estimate, not the sense. And when the counting task is set against a stricter method that requires actually detecting individual beats, performance on the two barely relates.
This is why we hid the clock from you, and why the interval was a random number of seconds rather than a tidy thirty. Not to be difficult -- to take away the arithmetic. If you don't know how long you counted for, you can't multiply a remembered heart rate by it. Whatever your score was, it is at least a little more likely to be about feeling than about sums.
A little. We are not claiming to have fixed a forty-year methodological problem with one random number in a museum.
What to take away
Two things, and they sit at different heights on the gauge below.
The first is solid and it is yours: there is a whole channel of sensation coming from inside you, most of it never reaches you, and the part that does is less reliable than you assumed. You have had this body your entire life and you have just discovered you are not especially good at reading it. That is worth a moment at a window.
The second is a caution, and it is the same caution as Exhibit № 39 one door along: a measure that is easy to run spreads much faster than a measure that is known to work. The heartbeat counting task is quick, needs almost no equipment, and produces a tidy number between zero and one. So it went everywhere -- into hundreds of studies, into claims about anxiety and autism and emotion -- and the argument about whether it measures perception or belief is still going on underneath all of them.
Interoception is real. Your insula is doing the work as you read this. The open question is whether the field's favourite ruler has been measuring the thing it is named after -- and, one floor down, whether the feeling of your own heartbeat is any part of why there is something it is like to be you at all. That one is Exhibit № 24, and it is still winning.
Take it further
The task is Rainer Schandry's, from Heart beat perception and emotional experience (Psychophysiology, 1981). The case against it is made most directly by Christopher Ring and Jasper Brener -- their 2018 paper is titled, with admirable economy, Heartbeat counting is unrelated to heartbeat detection. For interoception as a whole, the keyword is interoception; A.D. (Bud) Craig's How Do You Feel? is the deep version and is very good on the insula. Lisa Feldman Barrett's How Emotions Are Made carries the modern descendant of James's argument, and is next door in spirit to Exhibit № 37.
If you want to try the real thing, the honest apparatus is a fingertip pulse oximeter (about the price of a paperback) and someone else to run the clock -- that removes the last of the arithmetic, which is the whole difficulty.