  Captions that describe or explain charts help improve recall and
comprehension of the depicted data and provide a more accessible medium for
people with visual disabilities. However, current approaches for automatically
generating such captions struggle to articulate the perceptual or cognitive
features that are the hallmark of charts (e.g., complex trends and patterns).
In response, we introduce VisText: a dataset of 12,441 pairs of charts and
captions that describe the charts' construction, report key statistics, and
identify perceptual and cognitive phenomena. In VisText, a chart is available
as three representations: a rasterized image, a backing data table, and a scene
graph -- a hierarchical representation of a chart's visual elements akin to a
web page's Document Object Model (DOM). To evaluate the impact of VisText, we
fine-tune state-of-the-art language models on our chart captioning task and
apply prefix-tuning to produce captions that vary the semantic content they
convey. Our models generate coherent, semantically rich captions and perform on
par with state-of-the-art chart captioning models across machine translation
and text generation metrics. Through qualitative analysis, we identify six
broad categories of errors that our models make that can inform future work.
