The Impact of Differences in Collaborators' Encoding Levels on Collaborative Retrieval: An fNIRS Hyperscanning Study

Abstract: Collaborative retrieval refers to the joint recovery of encoded information by two or more individuals through social interaction. Although this process typically yields collaborative inhibition relative to nominal groups, it concurrently generates a post-collaborative facilitation effect that enhances subsequent individual retention. While previous studies have highlighted encoding level as a crucial moderating factor, they have predominantly focused on group-level manipulations rather than on the effects of within-group encoding disparities. By incorporating functional near-infrared spectroscopy (fNIRS), this study investigated how such disparities influence inter-brain synchrony (IBS) and directional neural coupling, thereby revealing the leadership–followership dynamics and information transfer patterns during collaboration.
A total of 160 university students participated in a single-factor between-participants experiment. The study manipulated the encoding composition of dyads across three conditions: differential encoding (semantic + perceptual), homogeneous high-level encoding (semantic + semantic), and homogeneous low-level encoding (perceptual + perceptual), while matched nominal groups served as controls. The experimental stimuli comprised 32 neutral, low-frequency, two-character words balanced for grammatical category and structure. The procedure involved four phases: an encoding phase, distraction task, collaborative (or individual) retrieval phase, and secondary individual retrieval phase. During the collaborative retrieval phase, fNIRS hyperscanning was employed to record neural activity. This study primarily focused on the prefrontal cortex and right temporoparietal junction.
The behavioral results indicated that, compared with nominal groups, homogeneous dyads exhibited collaborative inhibition, whereas differential dyads (semantic + perceptual) effectively eliminated this inhibition and enhanced post-collaborative individual retrieval, particularly benefiting perceptual encoders. In terms of neural activity, the results showed that differential encoding strengthened IBS in the right middle frontal gyrus (BA10) and right angular gyrus (BA39), with this synchrony positively predicting post-collaborative retrieval accuracy. Granger causality results further revealed the directional characteristics of the IBS, demonstrating a significant information flow from semantic encoders to perceptual encoders in the differential condition. This suggests a leader–follower dynamic in which semantic encoders guided the retrieval process.
In summary, the present study demonstrated that differential encoding composition promotes deeper social interaction, effectively eliminating collaborative inhibition and fostering post-collaborative facilitation. Inter-brain synchrony serves as a critical neural mechanism underlying the establishment of a leader–follower dynamic, thereby facilitating the effective transfer of information from semantic to perceptual encoders. These results provide empirical support for the optimization of collaborative memory through within-group encoding disparities. This study offers a novel perspective on the role of encoding levels and contributes to a deeper understanding of complex social–cognitive processes from the perspective of interpersonal neuroscience.