Recenttechnologicaladvanceshaveenabledhumanuserstointeractwithcomputersinwayspreviouslyunimaginable.Beyondtheconfinesofthekeyboardandmouse,newmodalitiesforhuman-computerinteractionsuchasvoice,gesture,andforce-feedbackareemerging.Despiteimportantadvances,onenecessaryingredientfornaturalinte