The heart in attention: evidence for cardiac phase effects in alerting but not executive control

Across two experiments, we examined the role of phasic cardiac fluctuations - whether the heart contracts (systole) or relaxes (diastole) - on two attentional mechanisms: executive control (EC) and alerting. Empirical evidence for cardiac phase effects in alerting has been missing, and studies on EC have found mixed results. Thus, we disentangled how cardiac fluctuations affect alerting and EC, separately and then together, using a subset of highly validated Attentional Network Test (ANT). EC was probed by requiring participants to resolve a conflict in an incongruent flanker stimulus. The stimulus was presented either during systole or diastole (Experiment 1, n = 48). Next, in Experiment 2 (n = 45), in addition to probing EC, we also probed alerting by providing participants, on half of the trials, with a cue to warn them of the onset of the stimulus. The cue was shown either during systole or diastole. Our results demonstrated that phasic cardiac fluctuations shape the more immediate alerting response to external cues, but not the subsequent executive control over conflicting information. Specifically, a cue that was presented at a time of increased cardiac output (during systole) elicited a more pronounced alerting effect than the same cue presented during diastole. Whether the stimulus appeared during systole or diastole had no impact on EC functioning. Overall, these findings contribute to the growing body of research on the interaction between cardiac signals and cognitive processes, emphasizing the selective role of systolic and diastolic phases in influencing alerting rather than executive control.