I am attempting to write a paper where I discuss how characters in one novel are objectified, while others in another novel are rendered sensations or are defined emotionally. Is there a word for the opposite of objectified? Sensitized? Can this word be applied to humans?
Subjectification, but with a health warning.
to identify with (a subject) or interpret subjectively. - Dictionary.com
The opposite of being the object is being the subject. This is true both in grammar, and more conceptually. Therefore, subjectification is the opposite of objectification.
However, a health warning before you run off and use it, especially in a paper. It's a fairly recent construction coming out of translations of French continental philosophy in the 1980s, particularly Foucault. (Quick overview at wikipedia). As it's not in wide use, you would have to engage specifically with those thinkers in your essay, citing a definition and showing the link to your argument. That might be more impact on your paper than you intend.
Explaining with a phrase may also be more readable. You might say that these characters come across as thinking people with complex emotional lives, instead of things.