Most of designers have experiences in designing for desktop or mobile interface. So do I. But three months ago, I was challenged to design for a large touch screen of food vending machine. The screen is 22 inches. What does this means?
The screen size is about 14 times larger than that of the average smart phone, and 8 times larger than that of iPad mini and 3 times larger than that of iPad. The significant difference in size has a real impact on user behavior.
It’s easy to realize that facing a larger screen size significantly increases the interaction efforts of tapping, typing, and moving between screens. They are more likely to access the interface at extended arm’s length and must hold their hands in the air, which increases fatigue.
Using smartphones, users can take in the whole screen at one glance. With a large screen, they must move their heads around to see all parts of the interface, which requires more effort from users.
Clearly, my story about large touch screen interface design went beyond that. Mentally, users also have different feelings about large touch screen. I first did an image board to understand where do people usually get access to large touch screen — the user context.
This image board helps me imagine a user standing in front of a large machine in a public space, using her index finger to touch the screen and trying to focus on its image without becoming distracted by the people around her. What she would be concerning at that moment?
The sense of familiarity
The most common used large touch screen design for everyone might be ATM and gas pumps, ticket kiosks or museums. But people are reluctant to touch large displays when they are not sure whether they will derive any benefit from the effort.
The matter of privacy
With larger touch screens, there is usually enough space for two or three people to interact at the same time. The negative side to screen sharing is that they offer little or no privacy for users of large, public touchscreen. With big touchscreen design, requiring users to provide sensitive information is problematic.
The interaction between human and machine
People make the effort to input their information for something as a return so unlike an app or website, there is a realtime communicate happening between users and the machine. The interface must work as a bridge between users and the machine.
All of these issues encouraged me to think critically about how to design in a user context.
A tough lesson I learned
With so many concerns and the pressure of moving fast in my mind, I first created a medium-fidelity interface with a layout and flow design for user testing. Since most users are unfamiliar with the big touchscreen interface, I drew my inspiration from Web design, using a header menu for the shelves and a footer menu to illustrate all the other functions.
- I expect users to draw lessons from their experience using websites when trying our interface.
- It would be easier for users to use the screen when all content stays in the middle of the screen.
I created a demo in Invision and received 90 percent position feedback from user testing. All respondents were able to complete a purchase easily and understand how the machines functioned. At that point, however, I encountered my greatest challenge with this project. In the actual machine interface, the buttons and menus did not respond readily to touch, which makes for a high error rate.
Consequently, I had to rethink my previous work.
Unlike other designs, large touch screen design is closely integrated with its specific context.
Clearly, since the screen is positioned at an angle in relation to the machine, when users view the machine, they always perceive both a hit target area and an off-screen hit area. Having all touchable items appear flat, as in my former design, makes the perceived hit target and on-screen area too limited for most users in a distracting environment.
The design for large touch screen is very different from that of my previous project; in this case, the user is expected to stand in front of the machine in a public space where people are talking or walking around. This special user context is actually the key to the project. I learned a lesson from the initial medium fidelity flat clickable design, and also acknowledged the gap between digital demo user testing and real situation testing. This project, therefore, has strongly changed my understanding about design and testing in a real-world context.
The final design is still under progress. Also, I didn’t talk much about privacy and human-machine communication design, if you are interested, you are welcome to read the whole project on my portfolio or contact me if you want to talk. Thanks for your time!