Rethinking LLM-Guided Visual Question Answering: Does Deeper Knowledge Integration Really Help?

Some questions about an image need commonsense or factual knowledge that its pixels do not contain. Large Language Models (LLMs) can supply this knowledge to Visual Question Answering (VQA) systems, but the depth at which their guidance should enter a vision-language model remains unclear. We prompt the 70-billion-parameter Llama~3.3 model to describe, for each question, the visual concepts to focus on, the distractors to ignore and the external facts needed. We inject this guidance into a frozen Vision Transformer (ViT) paired with an instruction-tuned Text-to-Text Transfer Transformer (T5) in two ways: decision-level late fusion and attention-matrix injection. On the Outside Knowledge VQA (OK-VQA) benchmark, and contrary to the common view that deeper is better, the shallow route wins: late fusion reaches 39.4% exact match, +10.0 points above an unguided baseline, while attention injection reaches only 31.8% under data-scarce fine-tuning. An LLM paraphrasing pipeline also enlarges the training set more than tenfold. The results suggest that integration depth should be matched to the data regime.