His performance style has been studied by academics who analysed gender, image and sexuality. Sheila Whiteley noted that Jagger's performance style "opened up definitions of gendered masculinity and so laid the foundations for self-invention and sexual plasticity which are now an integral part of contemporary youth culture". His stage personas also contributed significantly to the British tradition of popular music that always featured the character song and where the art of singing becomes a matter of acting—which creates a question about the singer's relationship to his own words. His voice has been described as a powerful expressive tool for communicating feelings to his audience, and expressing an alternative vision of society. To express "virility and unrestrained passion" he developed techniques previously used by African American preachers and gospel singers such as "the roar, the guttural belt style of singing, and the buzz, a more nasal and raspy sound". Steven Van Zandt wrote: "The acceptance of Jagger's voice on pop radio was a turning point in rock & roll. He broke open the door for everyone else. Suddenly, Eric Burdon and Van Morrison weren't so weird – even Bob Dylan."