In the hollow center of a new game called 'Time Traveler,' tiny, realistic, three-dimensional human beings are sawing, shooting, choking, stabbing and kicking one another with alarmingly real visual and sound effects. The characters playing across the console aren't animated gremlins or cute little plumbers. The crowd of scruffy young people gathered around the glowing console at the Time Out arcade in the Springfield Mall senses it, is riveted by it. We're talking about the local video arcade, where something new and nasty is going down. A stab wound in the gut, a boot kick to a man's tender parts. A human head bursting into flames near the Gap. We're talking chainsaws sputtering at the nape of a man's neck right here in the shadow of Montgomery Ward's.