Analyzing Top 40 hits from the mid-1960s through the first decade of the 2000s, they find an increasing percentage of pop songs are written using minor modes, which most listeners—including children—associate with gloom and despair. … While conceding that pop fans may not be consciously aware of a preference for more complex music, the researchers speculate that "musically untrained listeners may recognize quickly and explicitly that a contemporary fast-tempo, major mode song (such as Aqua’s Barbie Girl) has something amiss about it besides the lyrics."