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How GRAMMARS, PROMPTS, and DIALOGUE FLOW come together to form a good VUI
WHEN A MAGICIAN fans out his deck of cards face down and asks an audience member to pick a card, any card, he's not actually allowing her to do so. Through a sequence of carefully-worded prompts, the magician guides her to the card she will ultimately select. If she selects a card the magician expects, the trick is a success and everybody is delighted. If not - and the magician gets flustered - the situation becomes awkward.
The properties of a voice user interface (VUI) are similar in that its success hinges on its ability to guide the caller step by step into eliciting responses that will enable the system to help solve a problem.
While there's certainly consensus on such a fundamental principle, the conflict emerges at the skeletal level of VUI design, which is comprised of three components that should work in sync with one another. First are the grammars, which encompass all the possible things an end user might say. Second are the prompts, which the system says to provoke a caller response. Third is dialogue flow, which is the way the entire structure is organized.
Grammatical Corrections
"I hate your stupid VUIs!" the end user screams as she hurls her iPhone at her VUI designer husband's head. "They never understand what I say!" To save the marriage, the husband stuffs more grammars into his next VUI design, thus allowing the system to comprehend a greater variety of enduser responses. Where a menu option allows end users to check account balances, the embattled designer simply adapts the system to also accept account balance, balances, balance, account, and alimony.
The problem with this idea, however, is simply statistical. The more items added to a grammar, the easier it is for recognition to go wrong by getting confused for some other homophonic option.
Susan Hura, founder of SpeechUsability and a boardmember of the Applied Voice Input/ Output Society (AVIOS), defines the programming of grammars as a balancing act between adding enough that the system recognizes common phrases, but not so much that recognition as a whole decreases. And, according to Melanie Polkosky, a human factors psychologist specializing in VUI...