Frontiers in Psychology
January 1, 2024
Naotsugu Tsuchiya, Peter Bruza, Makiko Yamada et al.
8 citations
A new hypothesis called Quantum-like Qualia (QQ) proposes that qualia—the qualities of conscious experience—are best described by the mathematical structure of quantum theory, rather than as points in a dimensional space. The standard view assumes qualia can be measured without changing them, but empirical findings show that internal attention can alter qualia during measurement. QQ treats qualia as observables, sensory inputs and internal attention as states, and measurement outcomes as probabilistic. This structure predicts that qualia can be indeterminate, which can be tested through order effects or violations of Bell inequalities. Confirmation would suggest that quantum mathematics offers novel insights into consciousness.
Frontiers in Psychology
January 1, 2023
Shigeru Taguchi, Hayato Saigo
4 citations
Human consciousness constantly shifts through time, yet each moment is experienced as "now." This duality, called "the standing-streaming now" in Husserlian phenomenology, can be precisely formalized using category theory: the structure of the "now" corresponds to a monoid, while viewing present moments as discrete points on a timeline corresponds to a coslice category. This mathematical framework clarifies differences between ordinary consciousness and meditative states, such as the "eternal now" described in early Buddhist scriptures (Pali Canon) and Dōgen's Shōbōgenzō, which remarkably reflect a monoid structure.
F1000Research
June 25, 2026
Kyoko Kusano, Hayato Saigo, Naotsugu Tsuchiya
Measuring the diversity of subjective experiences (qualia) is difficult. A new mathematical approach, derived from category theory, offers two indices—'generalized magnitude' and 'spread'—to quantify how varied a person's internal structure of sensations is. In an experiment with 120 participants who rated similarities among color and emotion words, both indices captured differences in qualia structures at the group and individual levels. The indices also reveal complex graphical features of these structures, providing a principled way to compare how diverse people's inner experiences are.
Consciousness and Cognition
May 1, 2022
Naotsugu Tsuchiya, Steven Phillips, Hayato Saigo
Perceived similarity between conscious experiences can be quantified, and category theory offers a framework for modeling these relationships. Earlier work treated similarity as binary—either present or absent—but many experiences involve graded levels of similarity. This paper introduces enriched category theory, which replaces binary arrows with more flexible relations, such as a measure of perceived dissimilarity. The authors argue that enriched categories can accommodate various types of conscious experiences. A key implication is that the Yoneda lemma in enriched category theory allows a quale to be characterized by its collection of relationships to other qualia, up to an enriched isomorphism.
Frontiers in Psychology
January 1, 2022
Naotsugu Tsuchiya, Hayato Saigo, Steven Phillips
The relationship between qualia (subjective experiences), the contents of consciousness, and behavioral reports is examined through the lens of category theory, specifically the mathematical concept of adjunction. While some theorists argue that reports of one's own qualia are inherently incomplete and inaccurate, hindering formal research, empirical researchers have still made progress in understanding qualia structure from such reports. The authors propose that adjunction captures nuanced aspects of this relationship, establishing coherence between two categories that are not equivalent but importantly related. This mathematical formulation clarifies conceptual issues and suggests new empirical experiments to test predictions about qualia and reports, advancing consciousness research.
Naotsugu Tsuchiya, Masafumi Oizumi, Makiko Yamada et al.
preprint
The mystery of consciousness—how subjective experience arises from physical and chemical brain processes—is one of modern science's greatest challenges. Approaches that define humans and animals solely by observable behavior cannot scientifically address the conscious experiences of patients with hallucinations or delusions, nor those of non-verbal patients, infants, or animals. Recently, researchers confronting consciousness directly have advanced empirical studies of the brain-consciousness relationship. This article reviews several promising frameworks for consciousness research and introduces the authors' own strategy: clarifying the structure of conscious experience, the structure of information generated by the brain, and the relationships between these structures. The mathematical tool of category theory is briefly introduced as a means to achieve this, along with future prospects.