  Interaction plays a vital role during visual network exploration as users
need to engage with both elements in the view (e.g., nodes, links) and
interface controls (e.g., sliders, dropdown menus). Particularly as the size
and complexity of a network grow, interactive displays supporting multimodal
input (e.g., touch, speech, pen, gaze) exhibit the potential to facilitate
fluid interaction during visual network exploration and analysis. While
multimodal interaction with network visualization seems like a promising idea,
many open questions remain. For instance, do users actually prefer multimodal
input over unimodal input, and if so, why? Does it enable them to interact more
naturally, or does having multiple modes of input confuse users? To answer such
questions, we conducted a qualitative user study in the context of a network
visualization tool, comparing speech- and touch-based unimodal interfaces to a
multimodal interface combining the two. Our results confirm that participants
strongly prefer multimodal input over unimodal input attributing their
preference to: 1) the freedom of expression, 2) the complementary nature of
speech and touch, and 3) integrated interactions afforded by the combination of
the two modalities. We also describe the interaction patterns participants
employed to perform common network visualization operations and highlight
themes for future multimodal network visualization systems to consider.
