Adopting a terse or verbose prompt style

As one part of developing a consistent “sound and feel” for the interface, you need to decide whether you will use terse or verbose prompts. Each has advantages and disadvantages, as described in Table 1:

Table 1. Prompt styles
Prompting style	Advantages	Disadvantages
Terse	Uses the fewest words possible; makes efficient use of time. Often leads user to respond tersely, producing well-regulated spoken responses that are easy to recognize.	If too terse, callers might misinterpret its meaning, especially if the intonation is incorrect. You must also take care to avoid sounding impolite.
Verbose	Sometimes perceived as less impersonal, more human.	Might lead to excessively long prompts, especially if you don't adhere to the guidelines on prompt length and wording. The perception that an application just keeps talking can cause significant user frustration. Might cause the user to ascribe an excessive level of intelligence to the system; if this proves inconsistent with the actual abilities of the system, the interface can fail rapidly. You can minimize this risk by telling users up front that they are speaking to a computer (for example, “Welcome to the automated banking system”). Verbose prompts and mistaken assumptions about system intelligence can also lead users to produce responses that are not in the active grammar.

Weighing demographic factors

Accepted standards for terminology, formality, and interaction style in spoken communication vary widely based on demographic factors such as age, culture, and socioeconomic status, as well as the subject matter or purpose of the conversation. Obviously, you will want to design your application to conform to these behavioral norms.

Using terse prompts

In most cases, the balance will tip in favor of terser, or more concise, rather than more verbose prompts. Keep in mind that “terse” does not equal “machine-like.” In fact, most expert call center operators use terse prompting to capture the information they need when filling forms for customer orders and reservations. You can recover a human feeling through the selection of a good voice for recording (warm, sincere, professional) and providing short but natural variation in the prompts. For example:

`System:`	`Super Club auto reservations. You can use this system to make, change or cancel reservations. What would you like to do?`
`User:`	`I'd like to make a reservation.`
`System:`	`For what city?`
`User:`	`Pittsburgh.`
`System:`	`And for what day?`
`User:`	`Thursday May the third.`
`System:`	`Your arriving airline flight?`
`User:`	`US Air 2329.`

A particularly advantageous way to provide variation is through the use of discourse markers such as "first," "next," "finally," and "now." Other useful discourse markers include "oh," "otherwise," "OK," and "sorry." Each of these words has its own function in linguistic discourse. To achieve a natural sounding dialog, it is important that they not be overused.

Using verbose prompts

If you elect to use verbose prompts, you will want to give careful consideration to the following:

Design your dialogs to accept multiple pieces of information in a single utterance, and to parse the input regardless of order. See Mixed-initiative application and form-level grammars.
Ensure the robustness of the vocabulary used and determine which expressions you will support.
Provide plenty of pauses to invite users to barge in.