What is the relationship between sensitivity to interoceptive stimuli and exteroceptive stimuli? This study explored the interaction between sensitivity to interoceptive stimuli, specifically the heartbeat, and exteroceptive visual perception. The relationship between these is thought to play a role in self-awareness by integrating the perception of external stimuli with internal states. Previous research that studied the effect of cardiac signals on visual perception has reported baroreceptor (located near the heart blood vessels that send messages to the brain about blood pressure and volume) stimulation is higher during the systole phase (when the heart pumps out blood). These studies (Pramme et al., 2014; Salomon et al., 2016) demonstrated a baroreceptor inhibitory effect when presenting stimuli during the systole phase. However, these studies relied on a discrete, trial-by-trial approach to examine this effect. It is hard to examine the bottom-up subconscious processes if each trial was short and isolated. The present study used a binocular rivalry paradigm (Carmel et al., 2010), to entrain perception with cardiac cycle for an extended time. The synchronized (in-phase) stimulus always pulsed systolic, whereas the unsynchronized (anti-phase) stimulus pulsed diastolic (when the heart refills blood, the baroreceptor is relatively silent). In contrast to baroreceptor inhibitory theory, we observed an opposite facilitatory effect – dominance duration was significantly longer for stimuli during systole phase compared stimuli in the diastole phase. Further, this effect persisted without participants' conscious awareness of heartbeat. The present results demonstrate that physiological operations such as heartbeat timing do affect conscious visual perception suggesting perception may be more embodied than is generally conceptualized.
Fan Gao (Sat,) studied this question.