Max Headroom in the phonetics lab

This report has been circulating, in slightly less detailed form, on the BBC. It describes researchers 'reading off' speech signals in a coma patient. Sadly, but not unexpectedly, the BBC story is a trimmed-down version of the New Scientist story (already under 700 words), with a few quotes from other brain researchers thrown in for good measure, and, of course, filled with suggestions that the man in the coma is about to be turned into Max Headroom. This is not entirely true.

First of all, from the NS article, it looks like the Boston University Speech Lab is responsible for this research, but I can't find any reference to the project on their website. The description is of an invasive technique, implanting electrodes directly in poor MH's brain. (His real name seems to be Eric, but one would think they'd have changed it for the purposes of reporting the research anyway, so I'm going to stick with MH.) Sadly, their computer can't recognize 'N-N-New Coke' in the output of this little bundle of neurons, but it can apparently distinguish /u/, /o/, and /i/, and do so with 80% accuracy. Evidently they tell MH to 'think hard about saying /u/' and he complies in his comatose state. Until the details come out, I'll be a bit skeptical about what's really going on.

Nevertheless, what is there on the BU speech lab website is interesting: first, brain imaging data for speech production, most notably the apparent location in the brain of certain articulatory signals. Second, a computer model which they use to situate what they think these groups of neurons are doing. I won't evaluate either one, but if we believe their brain maps, and if we believe they've stuck the electrodes in the right place, then it seems like they are really reading off something like articulatory information.

This is somewhat interesting once you realize that the actual form that articulatory information takes is still up for debate. On the one hand, there's the fairly obvious theory that, when we speak, we just send instructions to the articulators. Of course, if sounds are stored in this articulatory format, then perception must involve something like the Motor Theory of speech perception, which means that you have some (presumably built-in) hardware for matching up speech sounds that you hear with the gestures that produced them. This is how you match up the sounds you hear with stored forms, which just tell you what to do.

On the other hand, a goal-based theory of production (subscription to Journal of Phonetics required) says something like the reverse. The information you need to send to the motor system is (mostly) a bunch of acoustic targets. You might also have articulatory targets, but the key thing is that you can just send 'I want a low f2' to the low-level system and it will work it out automatically, presumably, again through some built in mapping. So when we map out what parts of the brain are lighting up when we say /i/ etc, we shoul consistently see things corresponding to these more abstracted features. If we don't, then we can't tell whether the goal-based theory is right.

Of course, this is not so easy to tell for /i/, since the mapping between acoustics and articulation for the vowel space is fairly trivial, but if we had enough brain data we should in principle be able to tell; do the bits that light up for particular sounds in production seem to correlate with acoustics or articulation? Clearly, the articulatory signals have to be there, but if we can't see the acoustics, we don't have any reason to believe in the goal-based theory. This is factoring out any methodological concerns, of course, which I take it are acute with brain imaging. But it would be interesting to look (and if anyone wants to hunt through the stuff on the BU Speech Lab web site and try and find data bearing on this question feel free).