Language models demonstrate remarkable capacity to generalize representations learned in one modality to downstream tasks in other modalities. Can we trace this ability to individual neurons? We study the case where a frozen text transformer is augmented with vision using a self-supervised visual encoder and a single linear projection learned on an image-to-text task. Outputs of the projection layer are not immediately decodable into language describing image content; instead, we find that translation between modalities occurs deeper within the transformer. We introduce a procedure for identifying "multimodal neurons" that convert visual representations into corresponding text, and decoding the concepts they inject into the model's residual stream. In a series of experiments, we show that multimodal neurons operate on specific visual concepts across inputs, and have a systematic causal effect on image captioning.

通过向文本转换器添加视觉信息，我们研究了冻结的文本转换器如何使用自监督视觉编码器和单一线性投影将一种模态的学习表示迁移到另一种模态，在转换器内部发现了模态之间的转换，并通过识别多模态神经元和解码它们注入模型剩余流的概念来验证其作用。通过一系列实验证明多模态神经元在特定的视觉概念上操作，并对图像字幕生成产生系统性的因果影响。

预训练纯文本Transformer中的多模态神经元