Human driving is a mix of both methods. When you're on a street you're familiar with, habit takes over, and you barely notice what you're doing. On an unfamiliar street, you're much more active as a driver. At some level, humans require driving situations to be predefined, in that they need to match a familiar template. Road designs are all standardized.
In other words, the more information you have about the driving conditions, the simpler the problem. If you have a map, then you need to watch for anything that deviates from that map. If you don't have a map, then you have to process the scene to generate the map on the fly. (And by "map," I mean the entire design of the roadway, not just the traditional GPS-correlated road layout.)