Pop Art emerged simultaneously in Britain and America in the late 1950s and early 1960s, using imagery drawn from advertising, comic books, film stars, product packaging and mass media as its primary subject matter. Where Abstract Expressionism had retreated into personal, emotional abstraction, Pop Art turned outward — aggressively, ironically, sometimes ambiguously embracing consumer culture. Andy Warhol's Campbells Soup Cans (1962) and Marilyn Monroe silkscreens challenged distinctions between fine art, commercial art and popular culture. Roy Lichtenstein borrowed comic book imagery and the Ben-Day dot printing process. Richard Hamilton's collage Just What Is It That Makes Today's Homes So Different, So Appealing? (1956) is often cited as the first Pop Art work. Pop Art asked: in a world saturated with images, what is an 'art' image? The question has not been answered.