The term "Afro-Cuban" is confusing to many, in particular since Cuban music already contains a mixture of African and European (mostly Spanish) roots. Why, then, call some Cuban music Afro-Cuban? Mainly as a way to emphasize the increased amount of African elements present in many of the island's rhythms and dances. These Africanisms tend to be present in varying degrees wherever Africans were brought as slaves, and include: call-and-response vocals (where a lead vocal alternates with a fixed, repetitive chorus), polyrhythm (layers of rhythms in a complex structure), syncopation (an emphasis on the up-beats of off-beats within a musical phrase) and improvisation (from variation to full-blown solos).