Each individual was used 4 times in this experiment, for a grand total of 36 "familiar" trials and 36 "unfamiliar" trials per subject.
For each group, summary statistics were generated for demographic and behavioral variables, as well as performance on fMRI task (percentage correct novel and familiar trials), and number of non-recorded responses.
This study found no post-trial peaks in plasma oxytocin across both stranger and familiar trials.
No changes in peripheral oxytocin were detected across the stranger and familiar trials.
Instead, we tested for a delay-dependent difference between "Remember" and "Familiar" trials.
Throughout the study, individuals in stranger trials were consistently more investigative and aggressive than those in familiar trials.
During the main study, 40 trials took place over 14 days of captivity, consisting of 20 stranger trials and 20 familiar trials (n = 80 individual trial responses).
During the pilot study, eight trials took place over 5 days of captivity, consisting of four stranger and four familiar trials (n = 16 individual trial responses).
However, as familiar individuals reduced aggression towards each other, it seems unlikely that negative associations were present throughout all of our familiar trials.
Thus, response times are unlikely to account for why posterior hippocampal activation differences between Remember and Familiar trials were larger for immediate than delayed trials.
Many studies have shown that more contextual information is retrieved during "Remember" trials than during "Familiar" trials (e.g., Perfect et al., 1996, QJEP).
