and treasure-gathering. Q*bert plays upon the user's sense of depth perception to deliver a novel experience. Popular culture Some games of this era were so popular that they entered popular culture. The first to do so was Space Invaders. The game was so popular upon its release in 1978 that an urban legend blamed it for a national shortage of 100 yen coins in Japan, leading to a production increase of coins to meet demand for the game (although 100 yen coin production was lower in 1978 and 1979 than in previous or subsequent years, and the claim does not withstand logical scrutiny: arcade operators would have emptied out their machines and taken the money to the bank, thus keeping the coins in circulation). It soon had a similar impact in North America, where it has appeared or is referenced in numerous facets of popular culture. Soon after the release of Space Invaders, hundreds of favourable articles and stories about the emerging video game medium aired on television and were printed in newspapers and magazines. The Space Invaders Tournament held by Atari in 1980 was the first video game competition and attracted more than 10,000 participants, establishing video gaming as a mainstream hobby. By 1980, 86% of the 13–20 population in the United States had played arcade video games, and by 1981, there were more than 35 million gamers visiting video game arcades in the United States. The game that most affected popular culture in North America was Pac-Man. It was released in 1980 caused such a sensation that it initiated what is now referred to as "Pac-Mania" (which later became the title of the last coin-operated game in the series, released in 1987). Released by Namco, the game featured a yellow, circle-shaped creature trying to eat dots through a maze while avoiding pursuing enemies. Though no one could agree what the "hero" or enemies represented (they were variously referred to as ghosts, goblins or monsters), the game was extremely popular. The game spawned an animated television series, numerous clones, Pac-Man-branded foods, toys, and a hit pop song, "Pac-Man Fever". The game's popularity was such that President Ronald Reagan congratulated a player for setting a record score in Pac-Man. Pac-Man was also responsible for expanding the arcade game market to involve large numbers of female audiences across all age groups. Though many popular games quickly entered the lexicon of popular