It’s rare that a book comes out that’s immediately hailed as definitive, but that’s what happened to Brian Seibert’s monumental and engaging cultural history, “What The Eye Hears: A History of Tap Dancing.” It’s an intriguing title, which is Seibert’s theme, that tap is both dance and music, movement and sound. When Seibert recently spoke about the book at Southampton Library, he concluded his talk with a brief improvisational performance. The audience went wild. Seibert was delighted, and the