<P> During the live shows, the final selection of participants, which has ranged from between 20 to 60 acts and include those that were chosen as Wildcards by the judges or received the Golden Buzzer, are divided into groups and compete against each other for viewers' and judges' votes . The general structure of the live episodes focuses first on four quarterfinals, and then two semi-finals, aimed at finding that season's finalists . Additional rounds are conducted when required (such as a "Top 8" or a "Top 10", depending on the season). Live episodes are broadcast weekly, and featured performances by guest stars, including previous winners of America's Got Talent . During these stages, the judges still provide feedback on an act's performance when it is over, and can use buzzers to prematurely end an performance before it is over; in the first season, the judges could not end a performance before it was over . Acts which don't secure a sufficient amount of votes by the public and / or the judges, are eliminated from the competition . </P> <P> Those that make it into the season's final compete against each other to secure the most votes from the public, with the number of finalists varying between seasons . The act which does is declared the winner for that season, in which they secure the programme's cash prize of $1 million, and, since Season 3 (2008), a chance to headline a show on the Las Vegas Strip . Between the fifth and eighth season, the winner was also made the headline act of a national tour with runners up following the final show, stopping in 25 cities . For season nine, however (2014), there was no tour; two shows were held in Las Vegas for the winner and some of the runner - up acts . (See #America's Got Talent Live, below .) </P> <Table> <Tr> <Th> Season </Th> <Th> Presenter </Th> <Th_colspan="4"> Judges (chair's order) </Th> </Tr> <Tr> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> </Tr> <Tr> <Th> </Th> <Td> Regis Philbin </Td> <Td> Piers Morgan </Td> <Td> Brandy </Td> <Td> David Hasselhoff </Td> <Td> N / A </Td> </Tr> <Tr> <Th> </Th> <Td> Jerry Springer </Td> <Td> Sharon Osbourne </Td> </Tr> <Tr> <Th> </Th> </Tr> <Tr> <Th> </Th> <Td> Nick Cannon </Td> </Tr> <Tr> <Th> 5 </Th> <Td> Howie Mandel </Td> </Tr> <Tr> <Th> 6 </Th> </Tr> <Tr> <Th> 7 </Th> <Td> Howard Stern </Td> </Tr> <Tr> <Th> 8 </Th> <Td> Heidi Klum </Td> <Td> Mel B </Td> <Td> Howie Mandel </Td> </Tr> <Tr> <Th> 9 </Th> </Tr> <Tr> <Th> 10 </Th> </Tr> <Tr> <Th> 11 </Th> <Td> Howie Mandel </Td> <Td> Mel B </Td> <Td> Heidi Klum </Td> <Td> Simon Cowell </Td> </Tr> <Tr> <Th> 12 </Th> <Td> Tyra Banks </Td> </Tr> <Tr> <Th> 13 </Th> </Tr> </Table> <Tr> <Th> Season </Th> <Th> Presenter </Th> <Th_colspan="4"> Judges (chair's order) </Th> </Tr>

Who has been judges on america's got talent