Neurocognitive mechanisms of collaborative recall

Research on collaborative memory shows that people recalling in groups rarely achieve optimal performance. Collaborative groups typically recall less than nominal groups, where performance for the latter is derived by pooling the non-overlapping information recalled by the same number of individuals working alone. While behavioural evidence has widely replicated this collaborative inhibition in free recall, little evidence speaks to the neurophysiological signatures of this counterintuitive phenomenon. Behavioural evidence also indicates that disruption to one's preferred recall strategy, resulting from processing others’ recalled information, is a key mechanism underlying this effect. We aimed to identify the neural signatures indexing the recollection process and their disruption during collaborative recall. In three experiments, we replicated the standard collaborative inhibition effect with an EEG-adapted procedure (Experiment 1), and recorded EEG while people recalled in groups or in isolation (Experiments 2a, 2b). Comparisons showed increments in N400 and theta power, the neurophysiological components associated with interference, at shorter intervals for the collaborative compared to the nominal groups. Stronger theta power for collaborative than nominal recall, and for speakers than non-speakers in collaborative groups, were also evident at longer intervals and suggest demanding reinstatement of memory associated with collaborative recall. Together, the results suggest distinct neural processes underlying collaborative inhibition, with neural responses at shorter intervals signaling processes that are consistent with strategy disruption (stronger interference signaled by N400 and theta power increments), and further increments in theta at later times suggesting more demanding reinstatement processes during collaborative remembering.