Why is this topic important?

Communication is defined as a process in which people generate meaning through exchanging messages. It plays an essential role in cultivating harmonious interpersonal relationships, improving work efficiency, and maintaining social cohesion. Importantly, individuals with autism spectrum disorder and schizophrenia are characterized by communication difficulties. However, an outstanding puzzle for researchers is how it arises: How does a novel interpersonal communication system emerge?

According to the "Shared Intentionality Hypothesis," human communication is a cooperative behavior of human beings, which may rely on shared intentionality or "we" intentionality. Shared intentionality can be described as the cognitive ability to share mental states such as intentions, beliefs, and emotions with others. Several studies have demonstrated that shared intentionality is a key feature of joint action, cooperation, and verbal communication in humans. However, the number of available studies about the impact of shared intentionality on the establishment of a novel communication system is limited, and the knowledge is incomplete.

In recent decades, scientists have used naturalistic and experimental methods to study how humans create communication systems. The studies based on behavioral science show that the communicator's personality trait, interaction level, perspective-taking, and working memory contribute to the communicative outcome. While both of the aforementioned aspects investigate the behavioral factors and neural phenomena associated with the establishment of the communication system, these two types of research are essentially separate. The relationships among the factors (based on behavioral science), the common neural pattern (based on neuroscience), and the effectiveness of communication are not studied. As a result, it cannot find out the mechanism behind the behavioral factors, the shared neural pattern, and the primary motivation factor that contributes to the establishment of a communication system. Moreover, it cannot ensure how a novel interpersonal communication system is established.

 What did we do?

An experimental paradigm called the coordinating symbolic communication game (CSCG) is designed and conducted. The present study investigates the psychological and neural mechanisms of establishing a novel communication system. We combined the CSCG with behavioral research (Experiment 1), fNIRS-based hyperscanning technique (Experiment 2), and hyper-tACS stimulation (Experiment 3). First, we hypothesize that high SI plays a crucial role in the process of establishing a novel communication system. Second, previous studies have shown that INS enhancement in the ToM regions contributes to successful communication. Thus, SI will enhance INS in the ToM regions, which will ultimately increase communicative accuracy in the process of establishing a novel communication system. Third, based on the fNIRS results consistent with the above predictions, Experiment 3 further investigated the causal relationship between INS and communication accuracy by introducing hyper-tACS stimulation. Prior to the CSCG, two participants in a dyad randomly received in-phase, anti-phase, or sham stimulation; we would expect to see this effect to improve INS and communicative accuracy during the coordination period (COP) under the in-phase stimulation compared with anti-phase stimulation and sham stimulation.

What did we find out?

Our behavioral and neuroimaging results showed that higher communicative accuracy was associated with higher levels of shared intentionality and stronger INS in the rSTG. Furthermore, INS in the rSTG increased significantly in the success group compared to the failure group under the experimental condition, but not under the control condition. We found positive correlations between INS, shared intentionality, and communicative accuracy. Interestingly, such INS enhancement partially mediated the relationship between shared intentionality and communicative accuracy. Additionally, time series analyses showed that INS in the rSTG could differentiate the success and failure groups and predicted the trial-cumulative accuracy at the early stage of communication. Finally, we used hyper-tACS stimulation to examine the causal role of the INS enhancement in the rSTG in producing higher communicative accuracy.

What makes our findings important?

Taken together, our behavioral and brain imaging results showed that the SI modulates the INS, which contributes to establishing a novel communication system. Furthermore, the SI and INS contribute differently to the communication outcome due to the different stages of creating the communication system. In establishing the communication system, the SI and INS benefit the communication effectiveness. However, when the communication system has already been built, the SI and INS will no longer contribute to the communication effectiveness. Finally, in-phase, anti-phase, and sham simulations are carried out to verify that the INS contributes causally to the communication effectiveness.