THRONE: An Object-based Hallucination Benchmark for the Free-form Generations of Large Vision-Language Models

Mitigating hallucinations in large vision-language models (LVLMs) remains an open problem. Recent benchmarks do not address hallucinations in open-ended free-form responses, which we term “Type I hallucinations”. They focus on, if at all, hallucinations responding to very specific questions—yes-no or multiple-choice questions regarding a particular object or attribute—which we term “Type II hallucinations”, and they often require closed-source models which are subject to arbitrary change. Additionally, we observe a reduction in Type II hallucinations does not lead to a congruent reduction in Type I hallucations; rather, it often increases. We propose THRONE, a novel automatic framework for quantitatively evaluating Type I hallucinations in LVLM free-form outputs. We use public language models (LMs) to identify hallucinations in LVLM responses and compute informative metrics. We evaluate a large selection of recent LVLMs using public datasets. Our results show advances on existing metrics are disconnected from the reduction of Type I hallucinations, and established benchmarks for measuring Type I hallucination prevalence are incomplete. Finally, we provide a simple and effective data augmentation method to reduce Type I and Type II hallucinations as a strong baseline.