Featured Article

Neurophenomenology of induced and natural synaesthesia

David J. Schwartzman, Daniel Bor, Nicolas Rothen and Anil K. Seth

Published: 21 October 2019

Philosophical Transactions of the Royal Society B, 374(1787), 20190030.

Synaesthesia is defined by the presence of additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli. For example, in grapheme-colour synaesthesia, the letter ‘A’ printed in black may elicit a red colour experience. A long-standing question in synaesthesia research is whether it is possible to artificially induce non-synaesthetic individuals to have synaesthesia-like experiences. This paper reviews the current literature on artificially-induced forms of synaesthesia, evaluating the resulting synaesthesia-like experiences against some of the widely agreed upon hallmarks of genuine synaesthesia. The paper also highlights the relevance of synaesthesia, and its induced forms, for investigations into the cognitive and neural basis of conscious perception. In addition, the described alterations in perceptual phenomenology observed in developmental forms of synaesthesia and the rapid onset of induced synaesthesia-like experiences have huge implications for the plasticity of perceptual phenomenology. Together, these dramatic alterations in experience have the potential to shed light on the underlying mechanisms that contribute to experiential content and, more broadly, the origins of synaesthesia.