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Mobile usage patterns often entail high and fluctuating levels of difficulty as well as dual tasking. One major theme explored in this research is whether a flexible multimodal interface supports users in managing cognitive load. Findings from this study reveal that multimodal interface users spontaneously respond to dynamic changes in their own cognitive load by shifting to multimodal communication as load increases with task difficulty and communicative complexity. Given a flexible multimodal interface, users' ratio of multimodal (versus unimodal) interaction increased substantially from 18.6% when referring to established dialogue context to 77.1% when required to establish a new context, a +315% relative increase. Likewise, the ratio of users' multimodal interaction increased significantly as the tasks became more difficult, from 59.2% during low difficulty tasks, to 65.5% at moderate difficulty, 68.2% at high and 75 …