Page 33 - Like me, or else... - Michelle Achterberg
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                                Social evaluation in childhood
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 Unbeknownst to the participants, others did not judge the profile, and the photos were created by morphing two children of an existing data base (matching the age range) into a new, non-existing child. Peer pictures were randomly coupled to feedback, ensuring equal gender proportions for each type of feedback. Deception was assessed using an exit interview with open questions, such as ‘what did you think of the game’, and ‘what did you think of the noises that you could delivered’. None of the participants expressed doubts about the cover story. Participants were familiarized with the MRI scanner with a practice session in a mock scanner. Then participants received instructions on how to perform the SNAT and the children were exposed to the noise blast twice during a practice session: once with stepwise build-up of intensity and once at maximum intensity. Participants did not hear the noise during the fMRI session, to prevent that pressing the button would punish the participants themselves. To familiarize participants with the task, participants performed six practice trials. After the practice session, one of the twins continued with the actual scanning session, while the other twin performed the WISC-III and other behavioral tasks. First-born and second-born children were randomly assigned to the scan session or behavioral session as their first task. When the first child completed the scanning session, he/she continued with the WISC-III and behavioral tasks while the other child participated in the scanning session.
Figure 1. Display of one trial of the Social Network Aggression Task (SNAT).
The SNAT consisted of 60 trials, three blocks of 20 trials for each social feedback condition (positive, neutral, negative), that were presented semi-randomized to ensure that no condition was presented more than three times in a row. The first block consisted of 7 positive, 6 neutral, and 7 negative feedback trials; the second block consisted of 8 positive, 6 neutral, 6 negative feedback trials; and the third block consisted of 5 positive, 8 neutral, and 7 negative feedback trials. The optimal jitter timing and order of events were calculated with Optseq 2 (Dale, 1999). Each trial started with a fixation screen (500 ms), followed by the social feedback (2500 ms). After another jittered fixation screen (3000-5000 ms), the noise screen with the volume bar appeared, which was presented for a total of 5000 ms. Children were instructed to deliver the noise blast by pressing one of the buttons on the button box attached to their legs, with their right index finger.
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