Discovered by Diana Deutsch, Deutsch's scale illusion is an auditory illusion produced by simultaneous ascending and descending major scales beginning in separate stereo channels with each successive note being switched to the opposite channel. With the left channel: C'-D-A-F--A-D-C'; and the right: C-B-E-G-E-B-C; the ear hears both: C'-B-A-G--A-B-C'; and: C-D-E-F--E-D-C. Two complex patterns are turned into two much simpler patterns.