Gibson Guitar has told Activision its wildly popular Guitar Hero video games infringe one of Gibson's patents, a claim that Activision has asked a U.S. court to find invalid, according to court documents. In a letter sent to Activision in January, Gibson said the games, in which players press buttons on a guitar-shaped controller in time with notes on a TV screen, violated a 1999 patent for technology for simulating a musical performance.