FIGURE 3.

(A) When HRV was regressed onto reaction time gaps, HF indicated a positive curvilinear relationship between parasympathetic stimulation and reaction time (DF = 45, R² = 0.053, p < 0.05). Dotted line represents the linear model (DF = 46, R² = 0.046, p > 0.05). Each point represents a single participant’s HF measured during the cognitive stressor. (B) When analyzing the sympathetic response, a reciprocal relationship was found with increasing LF resulting in decreasing reaction time gaps (DF = 45, R² = 0.117, p < 0.05). Dotted line represents the linear model (DF = 46, R² = 0.10, p < 0.05). Each point represents a single participant’s LF measured during the cognitive stressor. (C) After combining sympathetic and parasympathetic responses to measure overall sympathovagal balance, LF/HF demonstrated a significant U-shaped relationship when regressed on reaction time (DF = 45, R² = 0.046, p < 0.0001). The interpolated value of the vertex was LF/HF 11.61 with a minimal reaction time gap of 143.5 ms. Dotted line represents the linear model (DF = 46, R² = 0.0083, p > 0.05). Each point represents a single participant’s LF/HF measured during the cognitive stressor.