How we perceive and react to the environment is not fixed; instead, it changes dynamically. This variability can be attributed to various factors operating at conscious and subconscious levels. Interoception, the processing of internal bodily signals such as heartbeats, has been found to modulate perception and action. However, the findings are partly inconsistent, and the underlying neural mechanisms are largely unclear. Sense of agency, the feeling of control over our actions and their outcomes, has also been found to shape our actions. Nevertheless, whether and how changes in our sense of agency influence our capacity to regulate behavior flexibly are largely unknown. The present thesis investigates the effects of cardiac interoception and the sense of agency on visual perception and action regulation. It includes five studies with behavioral and electrophysiological data from healthy human participants.
The Influence of Cardiac Interoception on Visual Perception (Study I and Study II)
In Study I, we investigated the perceptual effects and electrophysiological mechanisms of cardio-visual integration by coupling the color change of a visual target with participants' heartbeats in dynamically changing displays. Participants' task was to identify the orientation of the visual target. We found that (i) reaction times increased when the target change coincided with strong cardiac signals (during systole), compared to when the target change occurred at a time when cardiac signals were relatively weak (during diastole); (ii) the co-occurrence of the target change and cardiac signals modulated the ERP amplitude and the beta power in an early period (~100 ms after stimulus onset), and decreased the lateralized N2pc amplitude and the lateralized beta power in a later period (~200 ms after stimulus onset). Our results suggest that the multisensory integration of anticipated cardiac signals with a visual target negatively affects its detection among multiple visual stimuli, potentially by suppressing sensory processing and reducing attention toward the visual target.
In study II, we investigated the spontaneous shifts of attention between the internal and external environment across the cardiac cycle. Two groups of flickering dots moved continuously and changed direction dynamically within the same spatial location of the screen. However, only the direction change of one group of dots was coupled with participants' heartbeats. Participants' task was to detect a brief color change in the moving dots. We found that (i) compared to the visual dots whose direction change occurred randomly within the cardiac cycle, the dots coincided with strong cardiac signals (during systole) induced decreased SSVEP power, while the dots that coincided with weak cardiac signals (during diastole) induced increased SSVEP phase synchronization; (ii) the coupling of visual stimuli to the systole led to a larger HEP but a smaller N2 component evoked by the color change; (iii) the increase in HEP amplitude was related to the decrease in N2 amplitude. Our results suggest cardiac signals automatically redirect attention from external to internal domains.
Both studies reveal the interplay between cardiac processing and visual processing and support the spontaneous shifts of attention between interoception and exteroception across the cardiac cycle.
The Influence of Cardiac Interoception on Action Regulation (Study Ⅲ)
In study Ⅲ, we investigated how cardiac signals influence response inhibition in a stop-signal task by coupling the occurrence of the stop signal with participants' heartbeats. The stop signal signified the cancellation of the prepotent motor response. We observed prolonged stop-signal reaction times, reduced stop-signal P3 amplitudes, and higher HEP amplitudes when the stop signal was presented during cardiac systole, compared to presentation randomly within the cardiac cycle. Furthermore, these effects were independent of the emotional attribute of the stop signal (emotional facial expression change or non-emotional color change). Our results suggest that the co-occurrence of the action-relevant external cue and cardiac signals makes it harder to cancel the prepotent motor behavior. This effect may be attributed to inhibited perceptual processes of the visual cue, heightened readiness for action, or impaired inhibitory control ability during systole.
This study reveals the impact of cardiac signals on response inhibition and supports the attentional trade-off mechanism between interoception and exteroception.
The Influence of Sense of Agency on Action Regulation (Study Ⅳ and Study Ⅴ)
Both Study Ⅳ and Study Ⅴ investigated the effect of the sense of agency on subsequent action regulation by adopting modified go/no-go tasks. The first experiment of Study Ⅳ modulated participants' sense of agency by varying the occurrence of action outcomes (present vs. absent) both locally on a trial-by-trial basis and globally regarding the overall probability of action outcomes within a block of trials (high vs. low). When participants' previous action led to an outcome (i.e., a happy face) compared with no outcome, they responded more accurately and faster to go cues, reacted less accurately to no-go cues, and made go decisions more frequently and faster to free-choice cues. These effects were even stronger when action outcomes occurred more frequently in a given block or several previous trials. The second experiment of Study Ⅳ further demonstrated that the effects of outcome presence on subsequent action regulation were independent of the emotional valence of the action outcome (a happy or an angry face). Taken together, Study Ⅳ provides behavioral evidence that a higher sense of agency as induced by the presence of action outcomes enhanced action readiness and suppressed response inhibition.
Study Ⅴ manipulated participants' sense of agency by varying the presence, predictability, and emotional valence of a visual outcome for a given motor action. Consistent with the results of Study Ⅳ, when participants unexpectedly did not receive any visible outcome following their action, they exhibited slower responses and lower hit rates to the subsequent go signal but higher rates of successful inhibition to the subsequent no-go signal, regardless of the emotional valence of the expected action outcome. Furthermore, enhanced inhibitory tendencies were accompanied by reduced N2 and P3 amplitudes, midfrontal theta power, and theta synchronization between midfrontal and medial-to-parietal areas, indicating that less top-down control is required for successful response inhibition after experiencing a low sense of agency. These findings suggest that feeling less in control in a preceding trial makes it easier to implement inhibitory control in the current trial.
Both studies reveal the facilitatory effect of sense of agency on subsequent action readiness and its inhibitory effect on subsequent response inhibition, and they uncover how the automatic evaluation of action effectiveness shapes our ability to regulate actions flexibly.
General Conclusions
Overall, the present thesis suggests that fluctuations in internal bodily signals can influence perception and action, indicating a strong link between mind and body. Additionally, the effectiveness of motor action can shape subsequent action tendencies. These findings shed new light on the theory of embodied cognition
