Interesting new research suggests that mechanical skin disturbances caused by pulsating blood vessels may significantly contribute to your perception of your own heartbeat. This is important because it means that skin may play a larger role in emotion than has been previously thought.

The researchers found that, in addition to a pathway involving the insular cortex of the brain — the target of most recent research on interoception — an additional pathway contributing to feeling your own heartbeat exists. The second pathway goes from fibers in the skin to most likely the somatosensory cortex, a part of the brain involved in mapping the outside of the body and the sense of posture.

This sounds surprising at first, but it makes perfect sense. There have been other instances where the functionality of perceptual systems overlap. For example, it’s been found that skin receptors contribute to kinesthesia: as the joints bend, sensations of skin stretch are used to perceive of joint angles. This was also somewhat surprising at the time, because it was thought that perception of one’s joint angles arose out of the receptors in the joints themselves, exclusively. The same phenomenon, of skin movement being incidentally involved in some other primary action, is at work here. We might be able to say that any time the skin is moved perceptibly, cutaneous signals are bound up with the percept itself.

In fact, I think this may be a good object lesson in how words about feelings can be very confusing. A few years ago, before the recent considerable progress in mapping the neural signature of interoception, the word ‘interoception’ was used to describe a class of perceptions—ones whose object was the perceiver. Interoception meant the perception of bodily processes: heartbeat, metabolic functioning, and so on. When scientists discovered a neural pathway that serves only this purpose, the word suddenly began to refer not to the perceptual modality, but exclusively to that neural pathway. Now that multiple pathways have been identified, the word will go back to its original meaning: a class of percepts, rather than a particular neural conduit.

The movement of facial skin and muscles around the mouth plays an important role not only in the way the sounds of speech are made, but also in the way they are heard… “How your own face is moving makes a difference in how you ‘hear’ what you hear,” said first author Takayuki Ito, a senior scientist at Haskins.

Note that this sentence says that facial movement doesn’t affect what you hear, it only affects how you “hear” what you hear. More on this below.

When, Ito and his colleagues used a robotic device to stretch the facial skin of “listeners” in a way that would normally accompany speech production they found it affected the way the subjects heard the speech sounds.

The subjects listened to words one at a time that were taken from a computer-produced continuum between the words “head” and “had.” When the robot stretched the listener’s facial skin upward, words sounded more like “head.” With downward stretch, words sounded more like “had.” A backward stretch had no perceptual effect.

And, timing of the skin stretch was critical—perceptual changes were only observed when the stretch was similar to what occurs during speech production.

These effects of facial skin stretch indicate the involvement of the somatosensory system in the neural processing of speech sounds. This finding contributes in an important way to our understanding of the relationship between speech perception and production. It shows that there is a broad, non-auditory basis for “hearing” and that speech perception has important neural links to the mechanisms of speech production.

“Listeners,” “hearing”… Why do I worry so much about these damn quotation marks? Because they point out an assumption we tend to make about perception: that there are objective sense data out there in the world, ready to be accessed through our senses. Within this model, secondary effects (caused by face pulling robots) are seen as tricks played on our minds. But this is backwards. The astounding implication of this research is that our minds are composed of these tricks; the tricks are what produce a stable reality that meets our expectations.

For example, when the researchers were listening to recordings of the words “had” and “head” in order to design their experiment, the shape of their faces must have affected their hearing. (At least, that’s what their research seems to imply.) So who can listen without “listening”? Who determines whether the word is really “had” or “head”—someone without any facial expression at all?

The paper itself, which I haven’t read, can be purchased here.