  Current web accessibility guidelines ask visualization designers to support
screen readers via basic non-visual alternatives like textual descriptions and
access to raw data tables. But charts do more than summarize data or reproduce
tables; they afford interactive data exploration at varying levels of
granularity -- from fine-grained datum-by-datum reading to skimming and
surfacing high-level trends. In response to the lack of comparable non-visual
affordances, we present a set of rich screen reader experiences for accessible
data visualization and exploration. Through an iterative co-design process, we
identify three key design dimensions for expressive screen reader
accessibility: structure, or how chart entities should be organized for a
screen reader to traverse; navigation, or the structural, spatial, and targeted
operations a user might perform to step through the structure; and,
description, or the semantic content, composition, and verbosity of the screen
reader's narration. We operationalize these dimensions to prototype
screen-reader-accessible visualizations that cover a diverse range of chart
types and combinations of our design dimensions. We evaluate a subset of these
prototypes in a mixed-methods study with 13 blind and low vision readers. Our
findings demonstrate that these designs help users conceptualize data
spatially, selectively attend to data of interest at different levels of
granularity, and experience control and agency over their data analysis
process. An accessible HTML version of this paper is available at:
http://vis.csail.mit.edu/pubs/rich-screen-reader-vis-experiences.
