Synesthesia
![From the 2009 non-fiction book Wednesday Is Indigo Blue.[3] Note this example's upside-down clock face.](/Images/godic/202502/14/Number_Form--colored3756.jpg")
![A number form from one of Francis Galton's subjects (1881).[7] Note how the first 12 digits correspond to a clock face.](/Images/godic/202502/14/Galton_number_form.svg3756.png")
![Regions thought to be cross-activated in grapheme-color synesthesia (green=grapheme recognition area, red=V4 color area)[46]](/Images/godic/202502/14/Synaesthesiabrain3756.jpg")
![Reaction times for answers that are congruent with a synesthete's automatic colors are shorter than those whose answers are incongruent.[3]](/Images/godic/202502/14/Stroop_interference3756.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.