Research on auditory features
that contribute to speech comprehension has pointed out the importance of
temporal cues and the slow amplitude envelope. Specifically, manipulating the speech
amplitude envelope degrades recognition of speech sounds and comprehensibility of
sentences and, further, it has been shown that speech comprehension is
relatively preserved even when the frequency content is disrupted if the speech
amplitude envelope is preserved. While previous studies have shown that electrical
potentials generated by neural activity during listening to speech correlate
with the speech envelope, and that the degree of this correlation predicts
speech comprehensibility, it has not been determined precisely which cortical
regions track the speech envelope.
In their recent study, Kubanek et al. (2013) recorded electrical
activity intracranially with electrode grids placed on left-hemisphere cortical surface in five epileptic patients undergoing pre-surgical mapping of seizure foci. During recording, the subjects listened to four
short stories narrated by a male voice. The stimulus amplitude envelope was computed as the sound power in
consecutive 50-ms time windows, as was power of high-frequency gamma activity (75-115 Hz) for each of
the recording electrodes. The results show that the speech amplitude envelope
is most faithfully tracked by human non-primary auditory cortex that surrounds
the primary auditory cortex located within the confines of the Heschl’s gyrus,
and that the gamma-band signal in these recordings correlates best with the
speech envelope. Using non-speech control stimuli, the authors further
demonstrated that the non-primary auditory cortical areas, while also tracking
amplitude envelope of melody, do track more specifically the speech amplitude
envelope. Higher-order structures (superior temporal gyrus and inferior frontal
cortex), in contrast, tracked the speech amplitude envelope more weakly but at
the same time even more specifically than the non-primary auditory cortical areas.
These findings provide important further knowledge
on the cortical mechanisms underlying processing of speech amplitude envelope. The
results reveal cortical areas that track the speech
amplitude envelope, and further suggest that there is a processing hierarchy
with the non-primary auditory cortical areas tracking the envelope of speech
more robustly but less speech-specifically than superior temporal gyrus and posterior inferior frontal gyrus (i.e., Broca's area) that are considered higher-order language areas.
Reference: Kubanek J, Brunner P, Gunduz A, Poeppel D, Schalk G. The
tracking of speech envelope in the human cortex. PLoS ONE (2013) 8: e53398.
http://dx.doi.org/10.1371/journal.pone.0053398
No comments:
Post a Comment
Any thoughts on the topic of this blog? You are most welcome to comment, for example, point to additional relevant information and literature on the topic. All comments are checked prior to publication on this site.