Neural sensitivity to syllable frequency and mutual information in speech perception and production

Many factors affect our ability to decode the speech signal, including its quality, the complexity of the elements that compose it, as well as their frequency of occurrence and co-occurrence in a language. Syllable frequency effects have been described in the behavioral literature, including facilitatory effects during speech production and inhibitory effects during word recognition, but the neural mechanisms underlying these effects remain largely unknown. The objective of this study was to examine, using functional neuroimaging, the neurobiological correlates of three different distributional statistics in simple 2-syllable nonwords: the frequency of the first and second syllables, and the mutual information between the syllables. We examined these statistics during nonword perception and production using a powerful single-trial analytical approach. We found that repetition accuracy was higher for nonwords in which the frequency of the first syllable was high. In addition, brain responses to distributional statistics were widespread and almost exclusively cortical. Importantly, brain activity was modulated in a distinct manner for each statistic, with the strongest facilitatory effects associated with the frequency of the first syllable and mutual information. These findings show that distributional statistics modulate nonword perception and production. We discuss the common and unique impact of each distributional statistic on brain activity, as well as task differences.This study was supported by a research grant from the European Research Council under the 7th framework starting grant program (ERC-STG #263318) to U. Hasson and by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC #1958126) and Social Sciences and Humanities Research Council of Canada (SSHRC #430-2013-1084) to P. Tremblay. P. Tremblay holds a Career Award from the “Fonds de Recherche du Québec — Santé” (FRQS). We thank Margaret Moreno for her help collecting data, Francesco Cutugno for advice on Italian phonetic resources, the MRI staff of the Functional Neuroimaging Lab at the Center for Mind and Brain Sciences (CIMeC) at the University of Trento, and all the participants