Left thalamo-cortical network implicated in successful speech separation and identification
Section snippets
Participants
A total of 11 right-handed participants whose native language was English were recruited for the present study. Two participants were excluded from the analysis because they performed near ceiling (89 and 95% accuracy, respectively) and consequently there were not enough incorrect trials to be analyzed. Nine participants (4 women and 5 men aged between 21 and 30 years, mean age = 26 ± 3.5 years) formed the final sample. None had any history of hearing, neurological, or psychiatric disorders.
Behavioral results
Fig. 1 shows the group mean proportion of trials on which both vowels were correctly identified as a function of f0 difference (Δf0). Participants performed well above chance even when the two vowels shared the same f0. The increase in Δf0 led to moderate, albeit significant, improvement in vowel identification, F(4,32) = 3.78, P < 0.051. Pairwise comparisons
Discussion
Auditory streaming is a critical stage in auditory perception that permits listeners to identify the various sound sources contained in the incoming acoustic wave. Here, using fMRI, enhanced brain activity was observed in left thalamus, superior temporal gyrus, Heschl's gyrus, and in the planum temporale when participants successfully identified two concurrently presented vowels as opposed to when only one of the two vowels was recognized. The results suggest that success in speech separation
Acknowledgments
This work was supported by grants from the Canadian Institute of Health Research and the Natural Sciences and Engineering Research Council of Canada. We wish to thank B. Dyson and J. Snyder for their comments on the manuscript and valuable discussion. We are particularly indebted to Peter Assmann and Quentin Summerfield for providing the vowel stimuli and to Virginia Penhune and Robert Zatorre for providing the statistical maps of the primary auditory cortex.
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