The Sound of Thought.

Andrea Moro, Professor of General Linguistics at the University School for Advanced Study in Pavia, writes for the MIT Press Reader about an interesting experiment:

At least since the pioneering work of Nobel Prize-winning electrophysiologist Lord Edgar Adrian we have known that no physical signal is ever completely lost when it reaches the brain. What we’ve more recently discovered is surprising: Apparently electric waves preserve the shape of their corresponding sound waves in non-acoustic areas of the brain, such as in the Broca’s area, the part of the brain responsible for speech production.

These findings shed important light on the relationship between sound waves and electric waves in the brain, but almost all of them rely on one aspect of the neuropsychological processes related to language: namely, sound emission decoding. Yet we know that language can also be present in the absence of sound, when we read (as what we are most probably experiencing at this very moment) or when we use words while thinking — in technical terms, when we engage in endophasic activity.

This simple fact immediately raises the following crucial question: What happens to the electric waves in our brain when we generate a linguistic expression without emitting any sound? […]

Remarkably, we found that the shape of the electric waves recorded in a non-acoustic area of the brain when linguistic expressions are being read silently preserves the same structure as those of the mechanical sound waves of air that would have been produced if those words had actually been uttered. The two families of waves where language lives physically are then closely related — so closely in fact that the two overlap independently of the presence of sound. The acoustic information is not implanted later, when a person needs to communicate with someone else; it is part of the code from the beginning, or at least before the production of sound takes place. It also excludes that the sensation of exploiting sound representation while reading or thinking with words is just an illusory artifact based on a remembrance of the overt speech.

The discovery that these two independent families of waves of which language is physically made strictly correlate with each other — even in non-acoustic areas and whether or not the linguistic structures are actually uttered or remain within the mind of an individual — indicates that sound plays a much more central role in language processing than was previously thought. It is as if this unexpected correlation provided us with the missing piece of a “Rosetta stone” in which two known codes — the sound waves and the electric waves generated by sound — could be exploited to decipher a third one: the electric code generated in the absence of sound, which in turn could hopefully lead to the discovery of the “fingerprint” of human language.

Intriguing, certainly, but the MIT imprint inspires a certain skepticism, and I don’t know enough about this stuff to have a sensible opinion. All thoughts, as always, are welcome.


  1. David Eddyshaw says

    no physical signal is ever completely lost when it reaches the brain

    I don’t understand this. It seems transparently false, to a degree where the writer must mean something quite different from what I am naively supposing him to be saying.

  2. Yes, that bothered me too.

  3. PlasticPaddy says
    Basically response is independent of signal strength (once signal is perceptible). Maybe DM can say more.

  4. David Eddyshaw says

    The connexion between Moro’s statement and the all-or-none law does not strike me as what you might call limpid; nor does the connexion between the all-or-none law and the stuff about sound that he subsequently gets into. If this is supposed to be haute vulgarisation, it’s not nearly vulgaire enough for me.

    If it were not for the fact that I have the utmost respect for all Chomskyite professors of General Linguistics, I might even have fallen into the error of thinking that his account of his work was to some degree incoherent.

    I think he’s implying that the patterns of activity in the brain induced by external stimuli are (as it were) iconic: they reflect some physical aspect of the stimulus itself (which on some level, at least, would be wholly unsurprising); but that more particularly, in the case of sound, that the shape of electrical waves in Broca’s area mirrors (somehow) the shape of the actual sound waves produced when people speak (or listen? or in general, whether speech is involved or not?) He then attaches great significance to the fact that similar electrical activity occurs in the brains of those imagining themselves to be saying words without actually saying them, as in the brains of those who actually do speak the words.

  5. That stuck out when I read it as well. What Edgar Adrian discovered could be reasonably described as the exact opposite of, “[N]o physical signal is ever completely lost when it reaches the brain.” The repeated references to “electric waves” in the central nervous system also concerned me. There is, of course, a great deal of information contained in the frequency with which action potentials are transmitted, but because of the All-Or-None Law, that frequency carries mostly intensity information, not phase information.

  6. I think the article can be saved by overlooking the sentence about Lord Adrian, which was not the first sentence in the MIT Press version and is really not important to the rest of the article, except to say people have been measuring electrical activity in nervous tissue for a long time and Adrian was a pioneer in this effort. The sentence could even be partially rescued by admitting that the signal is not lost when (at the instant) it reaches the brain but goes on to have effects in the brain, although Adrian is not famous for this revelation.

    Moro is not clear about what electrical brain waves were recorded or how it was determined they were correlated with sound waves. Perhaps they were like EEG waves and they had the same cadence as the sound waves. Then seeing a similar pattern of electrical waves when the patient silently read the words would be interesting.

    I’m a bit surprised MIT Press’s reviewer didn’t ask that the Adrian reference be replaced by a reference to Bell and Magendie.

  7. I read the 2015 PNAS paper reporting the actual experimental results, and the actual results seem a lot less interesting than the way they are described in that book excerpt.

  8. I agree. The paper is underwhelming. For example, fig. 1 purports to show a cross correlation between the auditory signal and the EEG signal. The auditory signal (“filtered envelope”) is the smoothed envelope of the 2750–3250 Hz audio band. That won’t show you much of beyond prosody and the presence of sibilants. It shows one largish peak toward the end, and another similar peak in the filtered EEG follows it 0.3 seconds later. Otherwise I don’t see much similarity between the curves. How much of the cross-correlation would remain if not for that one peak? The cross-correlation “peak” is quite broad, too. It’s really unconvincing as showing anything.

  9. David Eddyshaw says

    I wonder if Moro’s Latin is quite as good as he supposes …

  10. no physical signal is ever completely lost when it reaches the brain

    I don’t understand this. It seems transparently false, …

    If it’s not false, where has the signal gone of whatever I had for lunch a week ago? Is this some sort of ‘The Boy who can’t Forget’ prognosis?

  11. So it’s one of those situations where a minor and/or unclear result is pumped up to where you can make a splash with it.

  12. David Marjanović says

    Maybe DM can say more.

    No, beyond platitudes like “never trust science journalism, including press releases by universities”.

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