Abstract
Two series of studies are reported dealing with (1) psychophysical characteristics and (2) interactions of visceroceptive and somatosensoric information processing. The first studies characterized detection, graduation and localisation of visceral as compared to somatic stimuli. The second series investigated somatovisceral discrimination, masking, and summation at different levels of awareness. Distension of the sigmoid colon served as standard model. The visceral stimulus was applied by a balloon probe in the sigmoid colon, the external abdominal stimulus by a ring-shaped stimulator at two abdominal sites. A forced-choice-paradigm with two observation intervals was applied (multiple staircase) to estimate interactions between somatosensation and visceroception. The visceral distension stimulus can be detected or discriminated correctly without conscious sensation. Visceral localization of stimuli requires conscious sensation. Combining visceral and somatic stimuli resulted in distinct elevation of visceral thresholds demonstrating somatosensory masking of the visceral stimulus. There are characteristic somato-visceral and viscero-somatic differences in masking and qualitative differences between implicit and explicit processing stages. Specific electrocortical reactions to visceral stimuli could be shown. Visceroception is represented on the highest functional level as a fairly independent submodality of body perception. There are several hints that visceroception and protopathic somatic sensitivity follow the same major paths and comprise the same ontogenetic origin. Perceptual interactions are determined by modality and awareness and depend on the task. The role of implicit and explicit body perception considering the body self and its significance in the context of consciousness are discussed.
Published Version
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