televised performances, forcing "pop stars had to have a visual presence". In the 1960s, the introduction of inexpensive, portable transistor radios meant that teenagers in the developed world could listen to music outside of the home. By the early 1980s, the promotion of pop music had been greatly affected by the rise of music television channels like MTV, which "favoured those artists such as Michael Jackson and Madonna who had a strong visual appeal". Multi-track recording (from the 1960s) and digital sampling (from the 1980s) have also been used as methods for the creation and elaboration of pop music. During the mid-1960s, pop music made repeated forays into new sounds, styles, and techniques that inspired public discourse among its listeners. The word "progressive" was frequently used, and it was thought that every song and single was to be a "progression" from the last. Music critic Simon Reynolds writes that beginning with 1967, a divide would exist between "progressive" pop and "mass/chart" pop, a separation which was "also, broadly, one between boys and girls, middle-class and working-class." The latter half of the 20th-century included a large-scale trend in American culture in which the boundaries between art and pop music were increasingly blurred. Between 1950 and 1970, there was a debate of pop versus art. Since then, certain music publications have embraced the music's legitimacy, a trend referred to as "poptimism". Stylistic evolution Throughout its development, pop music has absorbed influences from other genres of popular music. Early pop music drew on the sentimental ballad for its form, gained its use of vocal harmonies from gospel and soul music, instrumentation from jazz and rock music, orchestration from classical music, tempo from dance music, backing from electronic music, rhythmic elements from hip-hop music, and spoken passages from rap. In 2016, a Scientific Reports study that examined over 464,000 recordings of popular music recorded between 1955 and 2010 found that, compared to 1960s pop music, contemporary pop music uses a smaller variety of pitch progressions, greater average volume, less diverse instrumentation and recording techniques, and less timbral variety. Scientific Americans John Matson reported that this "seems to support the popular anecdotal observation that pop music of yore was "better", or at least more varied, than today's top-40 stuff". However, he also noted that the study may not have been entirely representative of pop in each generation. In the 1960s, the majority of mainstream pop