The work of experimental physiology researchers, such as Gyorgy Adam (1998) and Oliver Cameron (2002), as well as the psychologist James Pennebaker (1982) have opened up our understanding of how our cognition, brain, and peripheral nervous system allow us to know about our internal states. Such research probes the ability of people to sense and perceive processes and events interoceptively or visceroceptively-sensation via the visceral organs, typically the gastrointestinal tract or cardiovascular system. In a series of experiments lasting decades, described in Visceral Perception: Understanding Internal Cognition, Adam and colleagues (1998) painstakingly measured the ability of human subjects to perceive visceral changes. While much of their work is of primary interest to physiologists, for the present purposes it suffices to emphasize these claims and implications:
• The classical conception of the viscera, emphasizing their autonomic (maintaining homeostasis) activity, has not generally taken into account that sensory nerves innervate these organs.
• There are “dim and murky” but experimentally verifiable unconscious and conscious perceptions of these organs’ states.
• Conscious perception of visceral or interoceptive changes will tend to be “contaminated” with skin/surface based “somatic” perception, making “pure” visceral perception very difficult to verify.
• While cognitive neuroscience has fixated on the central nervous system, humans unconsciously and experientially are affected by various peripheral nervous system activities in the insides of their bodies, appropriately titled internal cognition (Adam, 1998).
Adam stresses the provisional, rather than the definitive, state of scientific knowledge of such concepts. Cameron (2002), in Visceral Sensory Neuroscience: Interoception, builds on Adam’s and other research, and attempts to contextualize what is known about internal body perceptions, skin and touch sensations, muscular control of movement, and other sensations. He addresses fundamental questions about how to taxonomize body knowledge, and writes that (pp. 274-275):
Rather than considering interoceptive processes, perhaps defining an overall bodily sense (or more than one-bodily senses) might be more appropriate…Would it not be more appropriate to define (as has been done by others) a bodily sense, including interoception, proprioception, labyrinthine function (i.e., the experience of the body in space), and other afferent information from the body?
The tentative appraisal of Adam and Cameron can only convey a sense of the complex nature of the phenomena at hand. Body knowledge, symptom perception, interoception, visceroception, and internal cognition are overlapping terms which need to be disambiguated. Yet this task is made all the more difficult because of the complexity of the problem of assessing how accurate people are at knowing their internal states.
Models of body knowledge are informed by practical medical and clinical needs. Physicians and clinicians routinely ask patients to report on their bodily sensations, while cognitive scientists, neuroscientists, and experimental psychologists often request subjects to verbally report on their perceptions. How true or “veridical” verbal reports are about objectively-measurable phenomena such as heart rate or blood pressure is a subject of debate. An extensive review by Pennebaker (1982) in The Psychology of Physical Symptoms of numerous results of studies measuring the abilities of normal humans to accurately report on physiological state found some limited evidence for accurate monitoring and reporting, but the bulk of data suggested people are poor at such tasks.
While this view may indeed represent something of a consensus, other authors (Fisher, 1966); (Adam, 1998) emphasize instances of relatively accurate capacity for interoception or perception of internal organ state, accuracy of perception of changes in external stimuli such as light or sound intensity (Stevens, 1975), practical necessity in clinical and medical contexts of asking patients to introspect and report on body state (Heilman and Valenstein, 2006) or numerous other perspectives that variously substantiate the accuracy and/or utility of verbal reports of sensation and perception. New data should be generated to shed light on two important (and overlapping) issues:
-the relative accuracy of verbal reports, which can be provisionally understood as representative fidelity to access to physiological state information.
-the neurobiological mechanism(s) by which people monitor and “get information” about their internal states.
The first issue above typically requires comparison of subject evaluations compared to objective measurements, while the latter usually involves imaging technology, such as EEG, fMRI, and other technologies. A model adequate to explain the results of both data sets will require bridging concepts that serve to link cognitive and biological levels of description. It should not be assumed at the outset whether or not information-processing models are up to that task. It may be that concepts from outside information-processing theory will be required to explain the data.