What techniques were used by the guards to dehumanize prisoners in Zimbardo's study?

The correct choice highlights the specific techniques used by the guards in Zimbardo's study to dehumanize the prisoners by stripping them of their personal identity. By addressing prisoners solely by their assigned numbers instead of their names, the guards reinforced a perception of the inmates as objects rather than individuals. This method effectively diminished the prisoners' sense of self and humanity, which is a fundamental aspect of the dehumanization process. Stripping personal identity was a crucial tactic for the guards, as it facilitated the exercise of control and dominance over the prisoners, fostering an environment where abuse and mistreatment could occur without moral repercussions.

Other options, while they might seem related to dehumanization, do not encapsulate the core method used in this infamous study. Physical punishment and food restriction could be more general methods of control but were not the primary tactics referred to in this context. Making prisoners perform menial tasks and randomly assigning unrelated tasks also lacks the direct impact of diminishing identity that addressing them by their numbers does, as it does not strip away their personal characteristics as effectively.