Right hemisphere at the right time: Electrophysiological evidence for right hemispheric syntactic processing in demanding condition

Abstract

Although syntactic processing is lateralized to the left hemisphere (LH), previous studies have revealed that the right hemisphere (RH) is also capable of processing syntactic information. However, the involvements of the RH are often discovered in the individuals with poorer performances to grammatical errors. Under such backdrop, it still remains unclear whether the involvements of the RH are a potential interference causing the poorer language performance, or on the contrary, the RH is recruited as an assistance to aid the LH dealing with the challenging conditions which were reflected in the poor performance. To better understand the causal relationships in between, the present study adopted and modified the artificial language (AL) learning paradigm with non-adjacent dependencies in Gómez (2002, 2005). Following the format, the stimuli included four dependency pairs: aXe, bXf, cXg, and dXh, consisting of two-syllable and three-syllable non-words. The difficulty of the AL was manipulated by the transitional probability of the intervening items (variability = 24 or 3, corresponding to the easy or the challenging condition respectively; details were demonstrated in the Table 1). In the experiment, there were four training-testing cycles. During the training session, participants learned the AL by listening monaurally to the strings. In the following testing session, they judged the grammaticality of the strings (containing grammatical pairs like aXe, bXf and ungrammatical pairs like aXf*, bXe*) based on the rule they acquired in the training session. Through the whole experimental procedure, participants’ brain responses were recorded. Together, fifty-six young right-handers without familial sinistrality background participated in the present study, and only half of them (twenty-eight participants) had successfully acquired the rule. When the proficiency of the AL were controlled to be equally high (accuracy > 80%) across the conditions, participants in the easy condition (variability of the intervening item = 24) showed a P600 grammaticality response only in their LH. On the other hand, the participants in the more challenging condition (variability = 3) showed bilateral P600 responses. To the end, our results favored in the explanation that when confronting a demanding task, the involvement of the RH is more likely to be an assistance rather than a hindrance.