Synesthesia
![From the 2009 non-fiction book Wednesday Is Indigo Blue.[3] Note this example's upside-down clock face.](/uploads/202502/14/Number_Form--colored0015.jpg)
![A number form from one of Francis Galton's subjects (1881).[7] Note how the first 12 digits correspond to a clock face.](/uploads/202502/14/Galton_number_form.svg0015.png)
![Regions thought to be cross-activated in grapheme-color synesthesia (green=grapheme recognition area, red=V4 color area)[46]](/uploads/202502/14/Synaesthesiabrain0015.jpg)
![Reaction times for answers that are congruent with a synesthete's automatic colors are shorter than those whose answers are incongruent.[3]](/uploads/202502/14/Stroop_interference0015.jpg)
Synesthesia (also spelled synæsthesia or synaesthesia; from the Ancient Greek σύν syn, "together", and αἴσθησις aisthēsis, "sensation") is a neurological phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. People who report a lifelong history of such experiences are known as synesthetes.