Assessing Social Alignment: Do Personality-Prompted Large Language Models Behave Like Humans?

The ongoing revolution in language modelling has led to various novel applications, some of which rely on the emerging "social abilities" of large language models (LLMs). Already, many turn to the new "cyber friends" for advice during pivotal moments of their lives and trust them with their deepest secrets, implying that accurate shaping of LLMs' "personalities" is paramount. Leveraging the vast diversity of data on which LLMs are pretrained, state-of-the-art approaches prompt them to adopt a particular personality. We ask (i) if personality-prompted models behave (i.e. "make" decisions when presented with a social situation) in line with the ascribed personality, and (ii) if their behavior can be finely controlled. We use classic psychological experiments - the Milgram Experiment and the Ultimatum Game - as social interaction testbeds and apply personality prompting to GPT-3.5/4/4o-mini/4o. Our experiments reveal failure modes of the prompt-based modulation of the models' "behavior", thus challenging the feasibility of personality prompting with today's LLMs.