Before emerging as a pop star, Madonna has spent her early years in rock music alongside her bands, Breakfast Club and Emmy. While performing with Emmy, Madonna recorded about 12-14 songs which resemble the punk rock of that period. Her early rock roots also can be found on the demo album Pre-Madonna. Stephen Thomas Erlewine noted that with her self-titled debut album, Madonna began her career as a disco diva, in an era that did not have any such divas to speak of. In the beginning of the '80's, disco was an anathema to the mainstream pop, and according to Erlewine, Madonna had a huge role in popularizing dance music as mainstream music. The album's songs reveal several key trends that have continued to define her success, including a strong dance-based idiom, catchy hooks, highly polished arrangements and Madonna's own vocal style. Her second album, Like a Virgin (1984), foreshadowed several trends in her later works. It contained references to classical works (pizzicato synthesizer line that opens "Angel"); potential negative reaction from social groups ("Dress You Up" was blacklisted by the Parents Music Resource Center); and retro styles ("Shoo-Bee-Doo", Madonna's homage to Motown).