Abstract
Consciousness science has traditionally proceeded by contrasting neural activity when a stimulus is consciously perceived against activity when the same stimulus is not perceived. This contrastive approach is well suited to locating neural correlates of consciousness, but it says little about why an experience has the particular character it does. A recent structural turn addresses this gap by comparing the relational structure of qualia with the relational structure of a candidate physical substrate. We review the main structure-matching programmes and what they offer beyond the contrastive approach. We then argue that all of them rest on an assumption that has never been tested directly, which we call the structural exclusivity assumption: That a neural structure matching the qualia structure reflects the neural substrate of consciousness itself, rather than merely the processing of information that can occur without conscious experience. The assumption is empirical rather than philosophical, and the standard structure-matching design cannot test it, because qualia and physical structures are estimated while the content is consciously perceived. We set out the design that would test it, and review the psychophysical and neural evidence currently bearing on it. That evidence consistently suggests that relational structure survives absence of awareness, though no existing study settles the question. We argue that structure-matching and contrastive designs must be combined, and consider what follows for the selection of candidate structures and for the promise of the dissolution of the hard problem of consciousness.