A Practical Guide to Designing Conversational Voice Interfaces

3. Navigation: It’s Difficult to Find Your Way in the Dark

VUIs can be difficult to navigate without a visual user interface for support, so it is important to simplify navigation and reduce the user’s cognitive load. You can do this by revealing only relevant information at each step through a shallow, but clear information architecture. A VUI must present no more than three options at any given point.

For example, only after a user has chosen a topic to talk about does Chattie elaborate by saying, “I will ask you some questions about your <topic>-related experiences. You can ask me for a sample answer or any word meaning. You can also ask me to mark a sentence for you to practice later. Shall we begin?” Presenting this information before the user selected a topic would require the user to remember it after arriving at this point. This would lead to cognitive overload, which can be incredibly frustrating for the user. To reduce friction, the VUI should also give the user the freedom to navigate back to the previous step or to the main menu.

When designing navigation, it is also helpful to consider the purpose of the VUI. For VUIs that have a specific purpose—such as Chattie, which is for practicing conversations—we suggest presenting the major features to the user up front. In contrast, for VUIs that fulfill many purposes, introducing just a few features, then letting the user explore others later works well. For example, people can use Alexa for checking weather, listening to music, and many other purposes.

4. Error Handling: Try to Score a Home Run

Try to cover all potential user responses when creating a conversation dialogue, but also create generic fallbacks for unscripted responses and unanticipated edge cases. It is also important to tailor fallbacks to include an explanation of why the system cannot complete an action to ensure a smooth experience. To add more value to an experience, you might consider offering an alternative that might be helpful to a distressed user.

For example, if a language learner asks Chattie to provide a specific sample answer that is not available, Chattie says, “I’m sorry, I can’t provide this particular sample answer, but I can give you a different sample answer. Would you like that?”

5. Persona: Hoooooman!

The personality and tone of your VUI will guide the user’s response, so it must be well thought out. What visual branding does for an app, nuances in voice such as tone, quality, and pitch do for a voice-based application.

For example, our usability testing showed that language learners wanted Chattie to be more like a friend than a teacher. Based on this feedback, we made Chattie’s tone friendlier, more encouraging, and natural by adding ad-libs such as “Great answer!” and “That dish sounds so yummy!” to our conversation script.

6. Iterate: Eat, Sleep, Test, Repeat!

Keep users in the loop throughout the design process and iterate based on their feedback. Having real-world conversations with people is a quick way of testing sample dialogues, understanding how users respond to prompts, and how they perceive the questions they’re asked.

It also helps to document unanticipated responses from users. For example, during Wizard-of-Oz usability testing, Chattie asked a participant, “What cutlery do you use to eat this dish?” The participant stumbled for a while because she misinterpreted cutlery as calorie. In preparing for the next test, we applied this feedback by identifying words that might be difficult for a language learner to understand. Then, if users stumbled, Chattie offered to explain these words to them without their asking for help.

In Conclusion

With over 40% of adults using voice technology every day, it is imperative that we, as VUI designers, strive to build seamless experiences. These six principles are a step in that direction. Their aim is to guide your process for designing for voice-based interactions. They incorporate learnings from different steps in the process that we followed when designing Chattie, including the following:

• validating the need of a VUI
• understanding the current scenario through a literature review
• competitive analysis
• surveys and interviews
• defining the information architecture
• iteratively scripting the conversation flow
• validating solutions through Wizard-of-Oz usability testing
• polishing the persona and tone of the VUI

We hope our principles will help other VUI designers in their explorations of VUX and bring clarity around potential successes and pitfalls.