Resting HR (RHR) and resting SC (RSC) measures were quantified as the average value across the three-minute baseline measurement period during which respondents watched the relaxing video. HRR and SCR were quantified with area under the curve with respect to increase (AUCi; Pruessner et al., 2003).11Using AUCi to quantify change in ANS activity in response to the countdown task allowed reactivity to signaled and unsignaled noise blasts in the countdown task to be captured with a single measure for each condition rather than the estimation of separate measures for change pre- and post-noise blast for both unsignaled and signaled noise blasts. A single measure of reactivity was preferable in order to limit the number of comparisons between ANS measures and multiple measures of psychopathic traits. The formula for AUCi is:

Where t_i is the interval of the time between measures and m_i is the measurement itself. Following Kavish et al. (2019), AUCi for the SSST was estimated with ANS values gathered during the 2 minutes in which subject prepared their speech and 2 minutes of speech delivery. For the countdown task separate AUCi measures were estimated for signaled and unsignaled trials. For both, ANS values included in the estimation of AUCi began with the 12-second anticipatory period before the noise blast and extended through the 20-second reactivity period after the noise blast. ANS reactivity measures for the signaled trials (trials 1 & 3) were then averaged for a single measure of reactivity during signaled trials, as were ANS reactivity measures for the unsignaled trials (trials 2 & 4). Descriptive statistics for all measures are presented in Table 1.

*Table 1*

Consistent with prior work in this area psychopathic traits were captured with range of measures corresponding to the breadth of traits subsumed in definitions of psychopathy including the Self-Report Psychopathy Scale-III (SRP-III; Paulhus et al., 2016), the Inventory of Callous-Unemotional traits (ICU; Frick, 2004), and the Sensation Seeking Scale – Form V (SSS-V; Zuckerman et al., 1978).