This US Patent describes an early prototype of the Maruishi PC system. This was a 1970s electro-mechanical device that takes an electrical signal from the special gear lever and then interprets it to pull the appropriate amount of bowden cable to move the rear derailleur to the correct position.
Electric shifting at a long-lost time time when Elvis really was still alive - what could be cooler than that?
This patent has a priority date of 1976. This is different from Japanese Patent # S51-35936, which has slightly different images and an earlier priority date of 1974.