Actually both can/are consumed by people. Field/dent corn is left to dry for ease of processing/harvesting and is usually used for animal feed (or other uses) as well as grinding into corn meal or corn flour for use as food in that manner.
The sweet corns (the type that's preferable for eating as corn on the cob, and other whole kernel food uses) is a lot sweeter tasting due to the higher sugar content in the kernels, and is harvested by the ear without letting it dry in the field.
There are also other types of corn that are specialized off shoots such as the popcorns, and other specialty corns (think white, and indian/flint corns) ..... all of which are specialized breeds/varieties descended from maize.
So yes field corn can and is eaten by people -- however, I'd not recommend doing so outside of grinding it down for corn flour or corn meal due to the really bland taste --- and definitely not without soaking it into a mush given the hard texture of the dried kernels. (I've tasted dried kernels of harvested field corn before, and it's not high on my list of things to have ever again).