Which one of these artists is not associated with the American Pop Art movement of the 1950s and 1960s?

Andrew Wyeth is not associated with the American Pop Art movement of the 1950s and 1960s because his work is fundamentally rooted in realism and exploring themes of rural American life, often characterized by a sense of melancholy and personal narrative. He is best known for his detailed, representational paintings, particularly his iconic works such as "Christina's World."

In contrast, the artists associated with the Pop Art movement, like Andy Warhol and Roy Lichtenstein, utilized commercial imagery and techniques from popular culture, such as advertising and comic strips, to challenge traditional boundaries of fine art. Jasper Johns, while often linked to Neo-Dada and influential in the transition to Pop Art, also engaged with symbols and subjects like flags and targets in a way that capitalized on popular culture's aesthetic. Wyeth's focus on individual and emotional storytelling sets him apart from the characteristics typical of the Pop Art movement, making him the correct choice in this context.