The only leads I could come up with are:
2. NGO-type stuff (like https://www.usip.org/the-missing-peace-symposium-2013-resources) as a place to start playing the game where you go to the References section, find the most interesting-sounding thing, and repeat until you find something worth spending some time on. As a rule, controlled opposition is going to let some interesting studies and books through because smart idealistic retards are going to join up thinking the “Anti-Child Trafficking Organization” is about opposing child trafficking.
Should mention that, IIRC, Nick Mason asserts the point of torture is generally to produce false confessions, mind control via depersonalization, and to traumatize a conquered population to make them more compliant.
I skimmed through the Amazon results for “torture psychology military” and made a list of the ones that sounded at least plausibly interesting from the descriptions. In order from most likely to least likely: