Final answer:
The mid-thirties blues music differed from its predecessors by incorporating an increased use of electric instruments, which added a new dynamic to the genre and helped lay the foundation for rock and roll.
Step-by-step explanation:
The shift in blues music during the mid-thirties was marked by an increased use of electric instruments. This evolution in the genre came about as musicians combined elements of gospel, blues, country, jazz, and R&B to create the new, electrifying sound of rock and roll. The innovation came with heavier rhythms, simpler lyrics, and melodies that resonated with the youth, facilitating the genre's swift rise in popularity.
Previously, blues had evolved from African-American spirituals and gained recognition during the Harlem Renaissance. Iconic figures like Bessie Smith, known as "The Empress of the Blues", were celebrated for their vocal prowess and emotional depth in lyrics, but it was the integration of electric instruments that defined the blues sound in the mid-thirties. The electrification of the blues enabled the genre to reach broader audiences and laid the groundwork for future musical movements.