  Encoding models have been used to assess how the human brain represents
concepts in language and vision. While language and vision rely on similar
concept representations, current encoding models are typically trained and
tested on brain responses to each modality in isolation. Recent advances in
multimodal pretraining have produced transformers that can extract aligned
representations of concepts in language and vision. In this work, we used
representations from multimodal transformers to train encoding models that can
transfer across fMRI responses to stories and movies. We found that encoding
models trained on brain responses to one modality can successfully predict
brain responses to the other modality, particularly in cortical regions that
represent conceptual meaning. Further analysis of these encoding models
revealed shared semantic dimensions that underlie concept representations in
language and vision. Comparing encoding models trained using representations
from multimodal and unimodal transformers, we found that multimodal
transformers learn more aligned representations of concepts in language and
vision. Our results demonstrate how multimodal transformers can provide
insights into the brain's capacity for multimodal processing.
