Segmenting nonsense: an event-related potential index of perceived onsets in continuous speech

Abstract

Speech segmentation, determining where one word ends and the next begins in continuous speech, is necessary for auditory language processing. However, because there are few direct indices of this fast, automatic process, it has been difficult to study. We recorded event-related brain potentials (ERPs) while adult humans listened to six pronounceable nonwords presented as continuous speech and compared the responses to nonword onsets before and after participants learned the nonsense words. In subjects showing the greatest behavioral evidence of word learning, word onsets elicited a larger N100 after than before training. Thus N100 amplitude indexes speech segmentation even for recently learned words without any acoustic segmentation cues. The timing and distribution of these results suggest specific processes that may be central to speech segmentation.

Figure 1

Performance on behavioral tests after training (percent correct) plotted against difference in N100 amplitude before and after training (before training minus after training). Subjects’ word learning as measured by the behavioral tests correlated with their N100 word-onset effect.

Figure 2

ERPs averaged to word onsets before and after training for the subjects showing the largest behavioral learning effects (high learners). After training, word onsets elicited a larger N100 at midline and medial electrode sites. Words also elicited a larger N400 after training.

Figure 3

ERPs averaged to word onsets before and after training for the subjects showing the smallest behavioral learning effects (low learners). After training, words elicited a larger N400, similar to that found for the high learners.