This 2015 study in Consciousness and Cognition discusses the phenomenological nature of the sense of boundaries (SB). Its authors, Yochai Ataria, Yair Dor-Ziderman and Aviva Berkovich-Ohana, base it on a single case: a meditator referred to as S, who has practiced mindfulness in the Satipatthana and Theravada Vipassana traditions for about 40 years and accumulated around 20,000 hours of meditation. The authors describe S as able to put his inner experience into words with unusual precision and clarity.
S was asked to shift between three states: his default state, the dissolving of the sense of boundaries, and its disappearance. From his descriptions, the authors identified seven categories that change across these states: the senses of internal versus external, time, location, self, agency (control), ownership, and center (a first-person, bodily perspective). Two other categories, the touching/touched structure and bodily feelings, did not fade away completely, even when the sense of boundaries disappeared.
Because it follows one person, the study offers a detailed account of one long-term meditator’s experience. It does not show what other meditators, or people new to practice, will experience.
Source: Ataria, Y., Dor-Ziderman, Y., & Berkovich-Ohana, A. (2015). How does it feel to lack a sense of boundaries? A case study of a long-term mindfulness meditator. Consciousness and Cognition, 37, 133–147. doi.org/10.1016/j.concog.2015.09.002
