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Can an LLM pretend to know nothing? Persona-based user simulation leaks the model's own knowledge

AspireAI community · arXiv (UserSim @ NeurIPS 2026)
When persona-conditioned model responses are read as respondent-level simulations, each response should reflect only that persona's knowledge, and a respondent written to know nothing should behave as if the model's knowledge were absent. This paper tests that and finds persistent favourable-item real-twin rating separation under low-knowledge and explicit-ignorance prompts. The methodology pairs real items with fabricated twins matched in surface form and screened so the variant requires no prior item-specific knowledge, giving a diagnostic contrast even in rating tasks with no correct answer. Across three knowledge-handling arms and five API endpoints from two model families, the personas did not fully suppress real-item familiarity signals, and the unfavourable-item contrast reversed sign across domain groups, sitting at plus 0.077 pooled against minus 0.359 where the scale asked about a documented hazard and plus 0.438 where it asked about a company or organisation, so a pooled analysis near zero conceals opposing differences. The authors are explicit that all estimates are conditional on twin construction and screening.
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