Bilingual lips: Motor activation for second language word processing

Current research suggests that motor articulatory representations are relevant for optimal speech processing under difficult circumstances. The challenging situation of a second language (L2) listener mimics this sub-optimal condition; therefore, activation of motor brain regions to support L2 processing is expected. This study aimed to investigate if the motor system associated with speech articulators exerts an influence on processing bilingual acoustic inputs. Thirty proficient bilinguals performed twice on a word-to-picture matching task: (1) while producing constant contraction of the orbicularis oris (OO) muscle interfering with the articulator’s movement and (2) while producing constant contraction of the first dorsal interosseus (index finger) muscle. Accuracy and reaction times (RTs) were collected from the bilingual task during the experimental and control conditions. Two-way repeated measures analyses of variance were conducted to assess if constant contraction of articulators yielded a significant effect on word recognition in L1 and L2. Word recognition was significantly slower in L2 compared with the native language (L1) during articulator contraction. Task accuracy in L1 was marginally better during the finger muscle contraction compared with OO muscle contraction, and no difference in accuracy was found in L2. An interesting distinct speed-accuracy trade-off strategy for L1 and L2 was observed. The findings support the hypothesis of a motor system facilitatory effect on processing acoustic inputs in bilinguals. The role of motor components in language processing has been studied in challenging linguistic environments, but little has been done to identify its role in L2 processing. This study used an innovative behavioral strategy to interfere with articulatory muscles during word recognition. Our results provide evidence of motor system processing support to L2 word recognition. In addition, a bilingual tendency to sacrifice speed for accuracy in L2 compared with L1 is suggested.