A cross-linguistic study of speech modulation spectra.

Languages show systematic variation in their sound patterns and grammars. Accordingly, they have been classified into typological categories such as stress-timed vs syllable-timed, or Head-Complement (HC) vs Complement-Head (CH). To date, it has remained incompletely understood how these linguistic properties are reflected in the acoustic characteristics of speech in different languages. In the present study, the amplitude-modulation (AM) and frequency-modulation (FM) spectra of 1797 utterances in ten languages were analyzed. Overall, the spectra were found to be similar in shape across languages. However, significant effects of linguistic factors were observed on the AM spectra. These differences were magnified with a perceptually plausible representation based on the modulation index (a measure of the signal-to-noise ratio at the output of a logarithmic modulation filterbank): the maximum value distinguished between HC and CH languages, with the exception of Turkish, while the exact frequency of this maximum differed between stress-timed and syllable-timed languages. An additional study conducted on a semi-spontaneous speech corpus showed that these differences persist for a larger number of speakers but disappear for less constrained semi-spontaneous speech. These findings reveal that broad linguistic categories are reflected in the temporal modulation features of different languages, although this may depend on speaking style.

Fluctuations in neuronal synchronization in brain activity correlate with the subjective experience of visual recognition.

The scientific study of subjective experience is a current major research area in the neurosciences. Coordination patterns of brain activity are being studied to address the question of how brain function relates to behaviour, and particularly methods to estimate neuronal synchronization can unravel the spatio-temporal dynamics of the transient formation of neuronal assemblies. We report here a biophysical correlate of subjective experience. Subjects visualised figures with different levels of noise, while their brain activity was recorded using magnetoencephalography (MEG), and reported the moment in time (corresponding to a noise level) of figure recognition, which varied between individuals, as well as the moment when they saw the figure more clearly, which was mostly common among the participants (thus less subjective). This latter moment is considered to represent psychophysical stochastic resonance (PSR). Fluctuations in neuronal synchronization, quantified using a diffusion coefficient, were lower in occipital cortex when subjects recognised the figure, for a certain noise level, but did not correlate with the moment of PSR. A different pattern was observed in frontal cortex, where lower values of the diffusion coefficient in neuronal synchronization was maintained from the moment of recognition to the moment of PSR. No specific pattern was found analysing signals from temporal or parietal cortical areas. These observations provide support for distinct synchronization patterns in different cortical areas, and represent another demonstration that the subjective, first-person perspective is accessible to scientific methods.