John Berger, the iconoclastic author of the seminal text on viewing art "Ways of Seeing," wrote of Spain's foremost art museum, "The Prado in Madrid is a unique meeting place. The galleries are like streets, crowded with the living (visitors) and the dead (the painted)."

Why the Prado in particular? Berger's view was a response to Diego Velazquez's paintings of beggar philosophers, Spanish nobles and court fools, and the immediacy with which they communicate their humanity. More than hyperrealistic and detailed brushwork, Velazquez does this by sowing doubt in the viewer's mind about the boundary between reality and representation.

The most revered of Velazquez's paintings, in this respect, is "Las Meninas," the outrageously clever group portrait of members of the Spanish court and a "photobomb" appearance by the artist. However, the boundary of the Prado's walls are too robust for that extraordinary image to have made it into the touring exhibition "Velazquez and the Celebration of Painting: The Golden Age in the Museo del Prado," which is now showing at the National Museum of Western Art, Tokyo.