Sunday, April 1, 2012

Some low-level research from TB East

One of the issues I have been thinking about for some time now concerns cortical oscillations and their potential role for speech processing. This topic continues to be debated vigorously. (At the Auditory Cortex Conference this coming September in Lausanne, I will be moderating a debate between Charlie Schroeder and Shihab Shamma; that should be quite lively ...) In a new paper, Anne-Lise Giraud and I outline a hypothesis what sorts of operations oscillations at different scales could be useful for. This paper makes some pretty strong predictions about the perceptual analysis of continuous speech and spike trains. We are obviously interested in feedback.

Giraud AL, Poeppel D.
Nat Neurosci. 2012 15(4):511-7. doi: 10.1038/nn.3063.

And on a similarly low-level topic: It has become commonplace to argue that as one ascends the auditory hierarchy, and especially as one goes from core to belt and parabelt areas, sensitivity to broadband (and complex) sounds increases. Tones and narrow-band sounds principally excite core fields, on this view.  In a pair of studies using fMRI and MEG, we crossed bandwidth and modulation frequency. We find that bandwidth (while crucial at the inferior colliculus) doesn't play as central a role as modulation rate. Both studies converge in a striking way, showing that auditory cortex is exquisitely sensitive to low modulation rates, and precisely in the range that forms the basis for spoken language processing (i.e. great below ~16Hz, best below 8 Hz). We are interested in figuring out how our findings reconcile with the single-unit data providing a very different perspective (at least with regard to spectral sensitivity).

Wang Y, Ding N, Ahmar N, Xiang J, Poeppel D, Simon JZ.
J Neurophysiol. 2011

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