Tonight’s episode of Mad Men (Season 4, Episode 2) paints (ha!) another 60s cultural reference before our eyes without giving even a tiniest hint at who or what it is. Here’s your general answer: Op Art. Here’s my educated guess: Bridget Riley.

Riley was a forerunner of Op Art, using simple shapes and colors to create the optical illusions that typified the movement. Popularized in late 1964 when an article ran in Time magazine coining the term, it demonstrates that even in the 60s, Americans would eat anything up if you shorten the number of syllables.

Like shoeless Bert Cooper before him, Roger Sterling arts up his office with pieces that spark reactions from not only from the audience, but from characters on the show. Prodigal son Freddie Rumsen sits next to a piece incredibly similar to Riley’s work and frustratedly remarks, “I feel like I’m being sucked in.” Whether or not this says more about Roger or Freddie, it would seem Mad Men has graduated from using costumes and historical events (obvious!) to references and set decor (subtle!) to immerse the viewer. Pretty Kruschev crucial in a period drama. Well done.