Interoceptive illusions as a tool to understand perception as an anticipatory process of expectations: a predictive coding perspective

Abstract: Emerging Embodied Predictive Coding frameworks propose that individuals’ experience of the internal milieu, or the body's internal state, is shaped by our beliefs and prior knowledge about the body's expected state, rather than being solely based on its veridical state. Here, we explore how predictive coding models and the free energy minimization framework provide insights into interoceptive processes, focusing on the mutual influence between cardiac and pain perception through the lenses of interoceptive illusions. Illusions offer an excellent starting point to understand perception as an anticipatory process of expectation, describing a process of error-based inference, whereby carefully crafted stimuli provide evidence for models (expectations) deviating significantly from reality. The first series of studies examined whether threat (i.e., pain) expectations could induce a misperception of heartbeat frequency, revealing that participants expected increased heart rate in anticipation of high-pain stimuli, and this belief was perceptually instantiated in their interoceptive reports, despite no actual change in heart rate. Importantly, when individuals experienced such cardiac misperceptions, it affected the amplitude of the Heartbeat Evoked Potential, a neuronal signature of the cortical processing of cardiac signals, suggesting the involvement of precision-weighted predictive mechanisms in the neural processing of cardiac signals. The second stream of studies serves as a counterpart to the cardiac illusion, where cardiac feedback was manipulated to induce pain expectations and misperceptions. Results showed that false faster cardiac feedback elicited heightened pain expectations, biasing perceptual pain judgments and physiological responses. This effect was evident in participants perceiving identical noxious stimuli as more intense and unpleasant, and experiencing a deceleration in heart rate consistent with the orienting cardiac response to threatening stimuli. This research highlights the reciprocal relationship between cardiac perception and pain processing within the framework of Embodied Predictive Coding. Understanding these mechanisms provides insights into how prior beliefs shape our perception and experience of internal states, contributing to the development of interventions for conditions involving altered interoceptive processing.