You know something’s up when Taylor Swift trades in the guitar-driven feel of her previous hits for a Max Martin four-on-the-floor dance groove. What’s up is this: Electronic dance music is well on its way to becoming the dominant pop flavor of the moment. And Grimes sits at its eccentric indie fringes, riding glitchy, synthy beats with a vocal sound a bit like a girlish young Madonna caught up in an Enya-like, reverb-cocooned trance. What Grimes — the Canadian singer-songwriter Claire Boucher — does has been called witch house, which is kind of a silly genre descriptor as these things go. But it does get at the built-in distance between her performances and the listener. Her latest album Visions is intriguing because from track to track, it conjures an evanescent alternate reality.