Some degree of adaptability is also present in adults, thus we get London cabbies with an enlarged hippocampus to accommodate all those streets.
There is also the fact that many brain functions are distributed; there are 30 or so brain areas involved in visual perception apparently so if you are missing one or two of those you maybe would still see but the quality of your visual sense might be different. And given that we cannot compare our subjective experience, simply because it is subjective by definition, we might never know if our experience differs from the norm.