Measuring Sentence Processing by Electroencephalography (EEG): New Technique Using M-Sequence Modulation

Studies using event-related brain potentials (ERPs) have reported electrophysiological responses to semantically and/or grammatically anomalous words embedded in a sentence for decades. Here we have successfully developed a technique with which we can objectively estimate the level of listeners´ speech comprehension using continuous speech sounds without linguistic anomalies. We used minute-long speech sounds whose amplitudes were modulated by an m-sequence (pseudorandom binary sequence). Eelectroencephalograms (EEGs) were recorded from Japanese speakers and were cross-correlated with the m-sequence. We identified a signal peak which was found only for comprehensible but not for incomprehensible (backward-played Japanese and Spanish) speech stimuli in an independent component cross-correlation function. The correlation time of the signal peak was 400 ms and the peak location on the scalp was Cz-Pz. The present study has thus shown that a minute-long EEG signal is sufficient for the assessment of speech comprehension.