Hearing Colors and Tasting Shapes: a Paradigm Shift in the Brain

This overview reviews various varieties of synesthesia and describes a general brain mechanism as the result of inheriting a genetic mutation for hyperconnectivity among brain areas. The automatic sensory joining of perceptual synesthesia is contrasted to deliberate contrivances and metaphor, the former being involuntary, spatially extended, durable and generic, memorable, and affect laden. Demonstrations show that sensory coupling occurs early in perception. Despite focal activations seen on scans, synesthesia is not localized in the sense of classical neurology, but exists as the dominant process in its underlying neural network at a given time. Synesthesia can help us understand more elusive aspects of human hought such as metaphor and creativity. Wassily Kandinsky and Paul Klee serve as examples of synesthetic artists, and sensory Form Constants are discussed. Synesthesia has caused a paradigm shift in two senses. For a long time, it was dismissed as not real because it contradicted settled theory despite synesthesia's perceptual reality being easily demonstrated in a number of ways. Today it is no longer regarded as a mere curiosity but as a challenge forcing fundamental rethinking about how brains are organized. The second shift is what synesthesia implies personally to everyone given that all brains have this latent capacity, and that systematic and lawful relations exist among sensory dimensions for synesthetes and non-synesthetes alike. Sensory substitution experiments, for example, demonstrate that cross-connection channels are already present. Explicitly, the senses feel separate enough to avoid confusion, but implicitly are more coupled than previously supposed.