Tsuchiya’s Relational Approach to Qualia
Neuroscientist Naotsugu ('Nao') Tsuchiya's relational and structural approach to consciousness—more specifically, to qualia—is not so much a theory of consciousness per se but more a fresh methodology, which he calls 'the Qualia Structure Paradigm.' It is “an alternative approach to characterize, and eventually define, consciousness through exhaustive descriptions of consciousness's relationships to all other consciousnesses.”
Verified*
Naotsugu Tsuchiya
Professor of Neuroscience & Researcher
Naotsugu Tsuchiya is a Professor in Psychological Sciences at Monash University, specializing in the physical substrates of consciousness. His work explores how subjective experiences can be supported by physical substrates, such as brain structure and its activity patterns. His interdisciplinary research employs mathematics, psychophysics, brain imaging, and computational models.
*This summary was verified by Naotsugu Tsuchiya on July 28, 2025.
Key Takeaways
Core Claim
Consciousness can be characterized by the structure of how experiences relate to each other across minds.
How It Works
Uses math from category theory to map qualia as relational structures rather than isolated properties.
Distinguishing Idea
Shifts focus from internal qualia to intersubjective patterns and structural similarities in experience.
Methodological Innovation
Introduces large-scale psychophysics and computational tools to empirically compare qualia.
Open Issue
Can mapping qualia relations clarify or replace the concept of qualia itself in explaining consciousness?
Tsuchiya’s Relational Approach to Qualia
Neuroscientist Naotsugu (‘Nao’) Tsuchiya's relational and structural approach to consciousness—more specifically, to qualia—is not so much a theory of consciousness per se but more a fresh methodology, which he calls ‘the Qualia Structure Paradigm’ (Tsuchiya, 2025). It is “an alternative approach to characterize, and eventually define, consciousness through exhaustive descriptions of consciousness's relationships to all other consciousnesses” (Tsuchiya & Saigo, 2021).
Mathematical Foundations
Tsuchiya's approach is founded in the Yoneda lemma from category theory, which deals with mathematical structures and their interrelations. By applying these mathematical concepts, the Qualia Structure Paradigm characterizes the structure of conscious phenomenology as a category, allowing for different conscious states to relate to one another.
Tsuchiya proposes several possible definitions of categories of consciousness—particularly “enriched categories” (Tsuchiya et al., 2022)—in terms of both level and contents of experience. These formal tools aim to clarify long-standing conceptual issues in consciousness studies, thereby fostering further theoretical and empirical work. If successful, the paradigm will offer strong support for relational and structural theories of consciousness (Tsuchiya & Saigo, 2021).
Empirical Developments
According to Tsuchiya, recent empirical work stemming from the paradigm has adopted and invented several novel methodologies. Moving beyond verbal reports and qualitative introspection, researchers have introduced large-scale online psychophysics to quantify intersubjective agreement—the degree to which different individuals agree about their experiences (Zhang et al., 2021).
In the domain of color qualia, earlier studies often viewed children's experiences as vague or inconsistent, based primarily on linguistic labeling tasks. However, using this paradigm, Moriguchi et al. (2025) demonstrated that the structure of color qualia in children is highly stable and closely resembles that of adults as early as age three.
Tsuchiya stresses that researchers are also collecting various types of data to quantify experiential similarities among different qualia. For example, in their paper “Is my ‘red’ your ‘red’?”, Kawakita et al. (2025) introduced a computational method called unsupervised optimal transport alignment, which provides a novel empirical approach to the long-standing philosophical issue of inverted qualia.
Surprising Findings
These empirical studies, Tsuchiya says, have yielded some surprising results. One key observation is that qualia similarity judgments are often asymmetric—for instance, the similarity one perceives when seeing red then pink can differ from the similarity perceived when seeing pink then red (Epping et al., 2023).
Such findings have led to the development of meta-level theoretical frameworks, including the Quantum-like Qualia Hypothesis (Tsuchiya et al., 2025). This hypothesis, inspired by ideas from quantum cognition (Busemeyer & Bruza, 2014), suggests that qualia may be structured by non-commutative (i.e., non-symmetric) relationships. Importantly, the hypothesis does not imply that quantum physics operates in the brain in any special way related to consciousness, but rather uses quantum-like formalisms to account for the observed structural features of experience.
Conclusion
Tsuchiya concludes that Qualia Structure approaches in empirical data collection coupled with novel computational structural analyses promises rapid development, being applied across wide areas of psychological domains that have been stalled due to the lack of methodology in characterizing qualia.
References
Ellia, F., & Tsuchiya, N. (2026). Explanation, scope, and perspective: sources of schismogenesis in consciousness science. Trends in Cognitive Sciences. https://doi.org/10.1016/j.tics.2026.03.005
Lee-Youngzie, Z., Tsuchiya, N., Robinson, M., Dietz, D., & Monti, M. M. (2026). Towards a mathematical structure of global phenomenal consciousness. Entropy, 28(6), 615. https://doi.org/10.3390/e28060615
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