Electrodes with extremely high- and/or low-frequency artifacts throughout the entire recording (M = 7.2 ± 3.6) were linearly interpolated using a model of the amplitude topography at the unit sphere surface based on all nonartifactual electrodes (Perrin et al., 1990). Epochs containing nonstereotyped muscular or technical artifacts were removed. An independent component analysis approach was applied
to further reduce artifacts such as eyeblinks, horizontal eye movements, or electrocardiographic activity. Independent components representing artifacts were removed from the EEG data by back-projecting all but these components (for details, see Schneider et al., 2008). Finally, all trials that still exceeded a threshold of 100 μV were rejected automatically. On average, 1.7% (range 0.3–3.1%) of all trials were removed for each AZD1208 mw AZD1152-HQPA participant. Prior to the statistical analysis, outlier trials were removed from pain ratings. To this end, the mean of intensity and unpleasantness ratings was calculated over nonpainful and painful trials separately, pooled across clips. Trials in which the ratings were below or above 3 standard deviations were excluded from further analyses. Based on this criterion, 0.29% of all trials were excluded (range 0.05–0.69%). The effect of viewing needle and Q-tip clips on
stimulus ratings was investigated by subjecting intensity and unpleasantness ratings to separate anovas with the factors visual stimulation (needle prick vs. Q-tip touch) and electrical stimulation (painful vs. nonpainful). As numerous electrical stimuli (360 painful and 360 nonpainful) were administered, it may be that habituation effects influenced the present findings (Condes-Lara et al.,
1981; Babiloni et al., 2006). To examine the possible influence of habituation on the effects in intensity GNA12 and unpleasantness ratings, additional three-way anovas, including the factor time (first and last 50% of trials within each condition), were conducted. The PDR was screened and corrected for outliers in the same way as in our recent study (Höfle et al., 2012). Eye blinks and other artifacts were removed in an interval ranging from 0.2 s before to 0.2 s after blink or artifact onset. Trials were excluded from further analyses if more than 50% of sample points within a trial were artifactual. On average, 1.2% of all trials were excluded following this criterion (range 0–3.1%). For all included trials, periods containing artifacts were linearly interpolated (Siegle et al., 2008). The PDR was normalised as follows: (data−baseline)/baseline. To establish the presence of significant effects in PDRs and to define a time interval for further analyses, point-wise running t-tests between the needle prick and the Q-tip touch trials were computed. To account for alpha error accumulation in multiple testing, time intervals were defined as being significantly different if each sample point within a 0.1 s interval reached a threshold of P = 0.05.