Psychophysiological Assessment
We used the BIOPAC MP150 system (BIOPAC System, Inc., Goleta, CA), a modular data acquisition and analysis system that is widely used in psychophysiological research, to assess psychophysiological activation, alpha asymmetry, and the ERN. We used AcqKnowledge software to filter and extract data.
Psychophysiological activation. The following measures were assessed during a 5-minute baseline resting phase and throughout the discarding and neutral tasks. We assessed skin conductance level (SCL) through a constant voltage of 0.5 V across two electrodes placed on the first and second fingers of the left hand. The total number of skin conductance responses (SCRs), which reflect the peaks in the SCL waveform, were extracted along with mean SCL. Heart rate variability (HRV) and heart rate (HR) data were collected via electrocardiogram (ECG) leads attached to both the left and right wrists, as well as the left ankle. ETCO2 was collected through nasal cannula and was measured in real time using the AcqKnowledge software rate calculation function. This function allowed for breath-by-breath measurement of ETCO2 percentage which then we statistically transformed to mmHg.
ERN . EEG data was recorded at 2000hz from six electrodes [‘Fz’,’O1’, ‘F3’, ‘O2’, ‘F4’, ‘Pz’] with a linked mastoid reference. All EEG post processing was conducted using the MNE software package (Gramfort et al., 2013). Data were bandpass filtered from 1 to 17Hz and EEG was segmented from 500ms before to 350ms after the commission of a response and baseline corrected from mean activity in the -500 to -100ms pre-response. Epochs with activity greater than 125mv were excluded for artifact. The ERN was measured as the difference between incorrect and correct responses at electrodes F3, Fz, & F4 50 to 150ms post response in line with prior literature (Gehring et al., 2018; Larson et al., 2010; Meyer, 2016; Meyer et al., 2020; Riesel, 2019) and confirmed with visual inspection of grand averaged waveforms.
Resting state alpha asymmetry . Alpha asymmetry was assessed during the baseline resting phase. Baseline EEG was segmented into 1-sec epochs. Artifact detection was the same as for ERN analyses. Artifact-free segments were decomposed into the frequency domain using multitaper fast fourier transform (FFT) implemented in the MNE software package. Frontal asymmetry indices were calculated by subtracting the natural log of the power of the left hemisphere electrode from that of the homologous right hemisphere electrode (In[right (F4)] – [left (F3)]).
Quality control . To minimize artifacts, participants were asked not to move during the study other than to press the appropriate button on the Go/No Go tasks (see below). They were closely observed by a research assistant throughout the study. Any movements that occurred were recorded on a testing form with the specific time that they occurred. If artifacts appeared in the waveform at those times, the sections of the waveform that included the artifact were excluded from the analyses. To ensure reliable data for the EDA analyses, prior to starting the tasks, we asked participants to hold their breath for a few seconds to verify that the signal responded to the breath-holding (EDA waveform should increase with breath-holding). Prior to starting the tasks, we visually inspected the ECG waveform to ensure that QRS peaks were being recorded properly. Additionally, during application of the EEG cap, each electrode was abraded (via a Q-tip) and re-jelled with abrasive electrolyte-gel up to three times, or until impedances as determined by an electrode impedance checker were less than 5 kΩ. The testing room in which the study took place was regulated at a temperature ranging between 71°F-73°F in order to ensure quality data collection.
For HRV, we applied a band pass filter (low frequency cutoff = 1 Hz; high frequency cutoff = 35 Hz; QRS peak threshold = 0.5 mV, which was adjusted as needed depending on the height of individual participants’ QRS peaks). For EDA, we first applied a low pass filter (1 Hz). The SCR threshold level was set at 0.02 microsiemens.