Skip n: A Simple Method to Reduce Hallucination in Large Vision-Language Models

Recent advancements in large vision-language models (LVLMs) have demonstrated impressive capability in visual information understanding with human language. Despite these advances, LVLMs still face challenges with multimodal hallucination, such as generating text descriptions of objects that are not present in the visual information. However, the underlying fundamental reasons of multimodal hallucinations remain poorly explored. In this paper, we propose a new perspective, suggesting that the inherent biases in LVLMs might be a key factor in hallucinations. Specifically, we systematically identify a semantic shift bias related to paragraph breaks (nn), where the content before and after 'nn' in the training data frequently exhibit significant semantic changes. This pattern leads the model to infer that the contents following 'nn' should be obviously different from the preceding contents with less hallucinatory descriptions, thereby increasing the probability of hallucinatory descriptions subsequent to the 'nn'. We have validated this hypothesis on multiple publicly available LVLMs. Besides, we find that deliberately inserting 'nn' at the generated description can induce more hallucinations. A simple method is proposed to effectively mitigate the hallucination of LVLMs by skipping the output of 'n'.