Abstract
Although Broca’s area is widely recognized to play an important role in speech production, neuroscientists still debate on its timing recruitment across different languages. In order to investigate the precise time course of phonological encoding for Mandarin Chinese, we applied real triple-pulse transcranial magnetic stimulation (tpTMS) and sham tpTMS within Broca’s area at five different time windows respectively (150 ms, 225 ms, 300 ms, 400 ms and 500 ms) in picture naming task in Mandarin Chinese. To exclude unspecific TMS effects and to make sure that the effects observed in the study were really due to stimulation at Broca’s area, we also conducted a control experiment by a different group of subjects. Significant increases in reaction times (RTs) were observed when real TMS stimulation at Broca’s area was applied at 225 ms, 300 ms and 400 ms time windows with a peak at 225 ms, compared with sham TMS stimulation at other time windows. Our findings support the hypothesis that the phonological encoding in speech production for Chinese language may approximately start from 200 ms and end around 400 ms post target onset, a little earlier than that from 355 ms to 455 ms for Indo-European languages.
Highlights
Spoken word production involves the coordination of several consecutive processes, such as conceptual preparation, lexical retrieval, phonological encoding, phonetic encoding and articulation
To exclude unspecific transcranial magnetic stimulation (TMS) effects and to make sure that the effects observed in the study were really due to stimulation at Broca’s area, we conducted a control experiment with TMS stimulation at Vertex as control site and sham stimulation at Broca’s area by different group of subjects
In the main experiment, the two factorial analysis of variance (ANOVA) analyses yielded a main effect of stimulation type and interaction between sham and active stimulation at Broca’s area, indicating that stimulation between sham and Broca’s area may have different effect on speech production
Summary
Spoken word production involves the coordination of several consecutive processes, such as conceptual preparation, lexical retrieval, phonological encoding, phonetic encoding and articulation. Based on a meta-analysis, Indefrey and Levelt (2004) estimated that the time course of phonological encoding starts from 355 ms and ends around 455–475 ms during the process of word production (Indefrey and Levelt, 2004), and this estimate has been widely supported by many studies of Indo-European languages (Salmelin et al, 1994; Sörös et al, 2003; Vihla et al, 2006; Hultén et al, 2009; Schuhmann et al, 2009). In a color adjective-noun picture naming task, Qu et al (2012) found more positive ERPs in the phonologically related condition in the 200- to 300-ms time window after picture onset Taken collectively, these findings provide empirical evidences for language-specific aspects in the process of phonological encoding
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