In 1991, STI began developing several games, including "Sonic the Hedgehog 2," which was released the following year. Though "Sonic the Hedgehog 2" was successful, the language barrier and cultural differences created a rift between the Japanese and American developers. Once development ended, Cerny departed STI and was replaced by former Atari employee Roger Hector. The American staff developed "Sonic Spinball", while the Japanese staff developed "Sonic the Hedgehog 3" and "Sonic & Knuckles". According to developer Takashi Iizuka, the Japanese team experimented with 3D computer graphics for "Sonic 3", but were unable to implement them with the limited power of the Genesis. After "Sonic & Knuckles" was completed in 1994, Naka returned to Japan to work on "Nights into Dreams" with Sonic Team.