“Signals: How Video Transformed the World” opens at New York’s MoMA, showcasing over 70 media works from the past six decades that capture how “artists have posed video as an agent of global change—from televised revolution to electronic democracy.” Highlights include Nam June Paik’s Good Morning Mr. Orwell (1984), Ant Farm’s Media Burn (1973), Martine Syms’ Lessons I–CLXXX (2014–18), and Dara Birnbaum’s Tiananmen Square: Break-In Transmission (1990, image).