Anyone with children knows that all parents suffer from hearing impairment: selective deafness. Oftentimes my children do things, like playing cassette tapes, that I don't pay much attention to. I rely on my wife to screen that sort of thing. So I didn't pay much attention for a couple of months when my youngsters kept dragging a tape player around the house with the same tape blaring. I just heard a snatch of music and tuned out.