Electrophysiological preprocessing

Data from the Cz and Pz midline electrode sites were averaged to compute the centroparietal LPP. Offline processing rereferenced EEG channels with a TP11 mastoid reference/TP9 linked ear clips in BrainVision Analyzer 2.1.2.327 (Brain Products GmbH, Germany). Next, a low cutoff filter of 0.1 Hz, a high cutoff filter of 40 Hz, and a notch filter of 60 Hz were applied offline. Independent component analysis (ICA), specifically a fast ICA restricted algorithm, was executed to semiautomatically remove ocular artifacts from EEG channel recordings. Tasks were segmented and then blocked by trial type for further processing. Artifact rejection was semiautomatic with parameters set as follows: maximal allowed voltage step of 50 μV/ms; maximal allowed absolute difference of values in intervals: 200 μV with a 200-ms interval length; lowest allowed activity in intervals: 0.5 μV with an interval length of 100 ms. All intervals contaminated with muscle, ocular, or non-neuronal electrical activity were marked 200 ms before and after stimulus presentation and removed. Program-flagged artifacts were inspected manually for artifacts. Nine percent of trials were rejected for artifacts in experiment 1, whereas 19% of trials in experiment 2 and 24% of trials in experiment 3 were rejected for artifacts.

ERP grand average waveforms were generated separately for each condition, referenced to a 150-ms prestimulus baseline preceding image onset. To isolate LPP maxima, we examined the morphology of the waveforms in the present study and followed conventions from previous research to define the LPP time window. In experiment 1, we examined the LPP from 400- to 800-ms poststimulus presentation to capture the maximal LPP peak known to be modulated during reactivity to emotionally salient cues (8, 13). In experiment 2, we examined the LPP from 400 to 1000 ms to capture the effects of attention regulation via mindfulness; attention regulation strategies are known to operate between 700 and 900 ms (14). In experiment 3, we examined the LPP from 400 to 1500 ms to capture the effects of evaluative emotion regulation via savoring; evaluative emotion regulation strategies are known to operate as late as 1500 ms (14). The LPP was scored by computing mean activity in microvolts in these windows on each trial. Statistical analyses were conducted on signal-averaged LPP data.