I think some cross cultural human studies might be a way of starting to answer this question. Looking at autists, or other non-neurotypical minds, would also be helpful. Studying sociopaths or psychopaths would also be important (they pass our society's behaviour filters, and yet misbehave). The errors of early AGIs (as long as they're left unpatched!!!) will also be very revealing, and let us try and trace the countours of non-human minds, and get insights into human minds as well. Formal philosophical measures (what kind of consistent long term behaviours can exist in theory?) may also help.

More ideas will no doubt spring to mind - if you want, we can design a research program!