The Uni-directionality of VUI

Compounding the linearity of speech is its unidirectional character. Just as time is a one way street, speech is a one-way medium. When you hear something, you can’t easily go back and listen to it again. Contrast this to reading a piece of text where you can readily scan a couple of paragraphs, or even pages, back and re-read the text.

Offer to repeat: one obvious way to alleviate this limitation is to offer the ability to repeat information. Of course, make sure that the user is aware that they can have information repeated to them by informing them of this ability at the beginning of the call and any time where important information is given out to them.

Offer help: crucial information such as instructions given at the start of the interaction should be available for the user to tap into at any point in the exchange. Offer instruction on how to access help at the beginning of the call and at moments where the user seems at a loss over what to do (e.g., at no-input or a no match).

Offer summaries: in interactions where information is being gathered from the user or given out to them in a step-wise fashion, a powerful technique to overcome the uni-directionality of voice interfaces is to offer users the ability to ask for summary of information collected so far.

The Time Linearity of VUI

Unlike graphical interfaces, voice interfaces are linearly coupled with time. When you are reading text on a web page, for instance, you can easily skip ahead with your eyes to the section that you are interested in. Not so with a voice interface, where you must patiently listen to one word before you can hear the one that follows it.

Avoid long prompts: obviously, unnecessarily long prompts will quickly tax the user’s patience. Long prompts explaining how the application works, for instance, may be inevitable and necessary with a novice user, but they should not be forced upon an expert user. Differentiate at the outset of a call between novice and expert users, and use short, to the point prompts with the experts.

Use short menus: the length of an alphabetically sorted drop down menu on a web page is a non-issue. The length of a menu in a voice interface on the other hand should not exceed five or six.

Put important information first: don’t annoy the user by having them wait through unnecessary noise for the information they need. Give them what they want upfront.

Allow interruptions: the ability to interrupt is usually a must have when dealing with non-novice users. People who know what they want to do, what to say and how to say it don’t want to wait for the system to finish talking before they give their response.

Offer short cuts for the user who knows what to do: another must for non-novice users are shortcuts that cut through menus and get the user to what they want to do or where they want to be in a menu structure.

Allow pauses: an enormous advantage that a graphical interface has over a voice interface is the ability to easily pause and pick up where you left off. We do this without even thinking about it when we are reading a piece of text. During interactions where the user may need to pause and do something, make sure that you offer that option to them. For instance, if the user needs to take down a long series of numbers (say a confirmation code), ask them to go ahead and get paper and pencil and to say, “continue,” when they are ready.