This image demonstrates the logic of one test used to demonstrate the reality of synesthesia. On the left is the image presented to participants, in which a triangle composed of 2s is embedded among a field of 5s. For non-synesthetes this triangle would be hard to identify (displays were presented for one second). However, for someone who experiences 2s as red and 5s as green, the triangle should be more easily identified. Subsequent research (see Hubbard et al., 2005; Hubbard and Ramachandran, 2005) has shown that this effect is not true of all synesthetes.

Image: Edward M. Hubbard. Image first appeared in Ramachandran, V.S., Hubbard, E.M.: Synaesthesia: A window into perception, thought and language. Journal of Consciousness Studies 8, 3-34, 2001, Fig. 1; with permission of APA. As author's own work, the APA journal has granted permission for use on Wikipedia and creative commons projects.

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