Stakeholders
Although stakeholders are usually aware of their objectives (e.g., higher rates of self-service, higher rates of task completion, shorter agent handle times), they may be naive about end users of the application (e.g, goals, abilities, limitations, preferences, etc.). Therefore, it is critical for the VUI designer to advocate for the end user. There will be no realized cost savings for an application if poor design drives traffic to other company channels.

Stakeholders tend to insist on designs that incorporate company jargon and mirror company infrastructure. A banking stakeholder, for example, may request a prompt that instructs, "please transit your ABA code to location XYZ now." End users may not understand this as a money transfer operation, and might hang up or opt-out to an agent. A designer with an understanding of the caller population would likely rephrase the prompt as, "Please enter the routing number for your bank. If you need help locating your routing number, press the star key."

To summarize, the stakeholder tends to approach application design from the needs of the business rather than the needs of the caller.

VUI Designer
The VUI designer is well-versed in observing, measuring, evaluating, and predicting human behavior. As an advocate for the caller, he/she should design from the caller's perspective but should not act as the sole subject matter expert for the target population. Designing with a certain set of heuristics in mind is fine as a starting point; however, at some point, potential users of the application should be involved as they possess a domain knowledge and a mental model that differs from the designer.

Despite the need for the VUI designer to advocate for the caller, it is also critical that the designer balance stakeholder objectives with caller objectives for optimal design results. New designers may focus too much on the caller objectives, only to dissatisfy stakeholders with elegant designs that don't meet requirements. For this reason, a key tool that the designer must employ is communication. A designer cannot allow a design to get too far along without getting input from stakeholders, otherwise quality and project timelines may be at risk.

To sum up, the VUI designer walks a fine line between meeting caller objectives and stakeholder objectives. It is not always easy or possible to achieve both. Often, there is a certain amount of compromise that must be made between the two. Unfortunately, it is frequently the caller objectives that are subordinated to other stakeholder objectives, but it is to be expected since it is the stakeholders who are funding application development.

Caller
While it might seem odd to categorize the caller as a "decider", it should be clarified that we are not suggesting that callers give direct input into application design. However, there is a rather large body of participatory design literature that suggests the value of subject matter experts in the design of applications. As noted earlier, subject matter experts can provide valuable information regarding how users will conceptualize the application. Further, they can provide feedback about their expectations for the task objectives. That being said, callers will not consider stakeholder business objectives; they most likely will be unaware of these, and even if they are, they probably will not care about them. Their perspectives will also be highly personalized, and may not necessarily represent all users.

To sum up, the caller should not be the final "decider" about an application's design. Callers, however, can be used for insight on an application design and for feedback on alternatives in the logic and prompting.

Developer
Developers will have valuable feedback on VUI designs. They may need to suggest alternative approaches because of hardware and networking constraints, as well as time and cost constraints.

Who is the Ultimate Decider?
There is no clear cut answer to this question. Ideally, the final VUI design for an application should involve a clear translation of the business requirements into design requirements in order to meet business objectives. To that end, it would appear that the design function should be a collaboration between the stakeholders and the VUI designers. Often, however, other variables influence the final design. The VUI designer is often in the unique role of playing a mediating role between all involved parties, and therefore must finalize VUI designs after taking into account the concerns of all parties.