a simple index for multimodal flexibility
Most interactive tasks engage more than one of the user's exteroceptive senses and are therefore multimodal. In real world situations with multitasking and distractions, the key aspect of multimodality is not which modalities can be allocated to the interactive task but which are free to be allocated to something else. We present the multimodal flexibility index (MFI), calculated from changes in users' performance induced by blocking of sensory modalities. A high score indicates that the highest level of performance is achievable regardless of the modalities available and, conversely, a low score that performance will be severely hampered unless all modalities are allocated to the task. Various derivatives describe unimodal and bimodal effects. Results from a case study (mobile text entry) illustrate how an interface that is superior to others in absolute terms is the worst from the multimodal flexibility perspective. We discuss the suitability of MFI for evaluation of interactive prototypes.
multitasking attention modality allocation mobile human-computer interaction multimodal interaction