Thilo Hinterberger (1,2), Petra Studer (2), Marco Jäger (2), Colette Haverty-Stacke (1), & Harald Walach (1)
(1) Division of Social Sciences, University of Northampton, UK
(2) Instituteof Medical Psychology and Behavioral Neurobiology, University of Tübingen, Germany
The presentation of pictures evokes clearly detectable responses in the electroencephalogram (EEG). Here, the question is addressed whether people show, as a paranormal effect, a pre-stimulus response prior to a sudden appearance of pictures. This presentiment effect could be visible in EEG activity even when people are not consciously aware of it. A study was carried out with 20 participants being exposed at randomised times to affective and non-affective pictures and to checkerboard stimuli. The pre-stimulus epochs for these stimuli were compared to pre-stimulus epochs before a hidden stimulation. A non-parametric statistical approach was chosen for the analysis of the one-second pre-stimulus interval. With checkerboard stimulation, only a marginally significant presentiment effect could be detected at the Pz electrode. Considering all picture stimuli, the analysis of all cortical channels merged revealed a significant increase of the EEG activity (z=1.71). Considering the affective pictures only, the significance was z=2.02. The difference between affective and neutral pictures revealed significant z-scores greater than z=2.0 at four of the six electrode positions. A control condition in which the monitor was covered showed no significant difference between the affective and neutral targets. The contrast of visible and covered picture stimulation revealed significance at C3 with p<0.02. For the visible pictures, the amplitude rankings at Cz were shifted towards higher ranks with p=0.01. The power in the delta band was significantly decreased with p=0.006 in picture stimulation. The checkerboard stimulation remained non-significant in the comparison between visible and covered conditions. The significant decrease in the eye movement channel during the pre-stimulus period for the visible conditions can be explained by a systematic eye blink of the participants at or after stimulus presentation which was less frequent before.
The results suggest the possible existence of an abnormal presentiment effect. As it is not visible in the averaged EEG curves this effect may not be time-locked to the stimulus and different for each participant. The missing significances for neutral pictures and checkerboard stimuli suggest that emotional affectivity is important for a presentiment reaction in the EEG. A tendency towards compensatory behaviour of pre-stimulus activity can be explained by theories such as the decision augmentation theory or the weak quantum theory.