Distant psychophysiological interaction effects between related and unrelated participants
Kittenis M., Caryl PG, Stevens P; Association 47th Annual Convention: Proceedings of Presented Papers, Vienna (67-76), 2004.
The aim of this study is to investigate possible remote psychophysiological interactions between sensorially isolated participants, using a protocol of photic stimulation and EEG measurements. It is an attempt to conceptually replicate past findings suggesting the presence of such interactions, and to clarify the role, (if any), of an existing emotional relationship and pre-session interaction between participant pairs. Forty-one unpaid volunteers were assigned to one of three groups. One of these consisted of thirteen related pairs of participants who reported sharing an empathic relationship, another of five unrelated pairs (i.e. randomly matched strangers), and the last of five single participants. Related pairs spent some time alone together before testing, whereas unrelated pairs did not know each other and did not meet until after the session; single participants were told they would be paired with someone they didnt know, but were not matched with anyone. Pairs of participants simultaneously listened to a recording of a progressive relaxation procedure including suggestions aimed to induce a hypnagogic-like state, which was followed by 15 minutes of continuous drumming; this procedure was intended to induce a similar alteration of consciousness in both participants. During the drumming period the EEG of one person of the pair (receiver) was recorded while the other (sender) was occasionally stimulated with randomly timed single photic flashes. For the single participants group the same procedure was followed but there was no sender to observe the flashes. EEG epochs that were time-locked on photic stimulation of the senders were taken from the continuous EEG record of the receivers. Similar randomly sampled epochs were taken from periods of no stimulation to serve as controls. According to the null hypothesis no difference would be expected between these samples, as sensory stimulation of the receivers was homogenous throughout the experimental period. Event-related evoked alpha power measures revealed a tendency for samples from remote photic stimulation periods to show larger deviations from pre-stimulus baseline than control samples; these deviations were in the same direction as normal responses to direct photic stimulation. This difference between remote photic stimulation and control periods was found to be significant for the related pairs group at p<0.023 (Wilcoxon signed-ranks test, two-tailed; N=13). Deviations of similar direction and magnitude were found in unrelated pairs (p<0.007 when combined with related group, N=18), while recordings from single participants (when no other person was stimulated) showed no such effect. Further patterns identified in the results and possible interpretations are discussed.
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