  Current speech agent interactions are typically user-initiated, limiting the
interactions they can deliver. Future functionality will require agents to be
proactive, sometimes interrupting users. Little is known about how these spoken
interruptions should be designed, especially in urgent interruption contexts.
We look to inform design of proactive agent interruptions through investigating
how people interrupt others engaged in complex tasks. We therefore developed a
new technique to elicit human spoken interruptions of people engaged in other
tasks. We found that people interrupted sooner when interruptions were urgent.
Some participants used access rituals to forewarn interruptions, but most
rarely used them. People balanced speed and accuracy in timing interruptions,
often using cues from the task they interrupted. People also varied phrasing
and delivery of interruptions to reflect urgency. We discuss how our findings
can inform speech agent design and how our paradigm can help gain insight into
human interruptions in new contexts.
