본 연구는 실시간으로 사용자 시선의 축(Axis)과 디스플레이 축을 일치시켜주는 사용자 중심 스마트워치 인터페이스가 스마트워치 사용성에 미치는 영향을 실험을 통해 살펴보고자 하였다. 이를 위해 스마트워치 인터페이스(2: 사용자 중심 인터페이스 vs. 기존 인터페이스)와 사용자 팔동작(4: 위 vs. 왼쪽 vs. 앞 vs. 아래)을 구분하여 응시시간, 반응시간, 정확도를 모바일 아이트래커와 실험도구를 이용하여 정량적으로 측정하였다. 실험 1에서 SMS 메시지, 일기예보, 스케쥴, 전화번호로 구성된 텍스트 자극을 제시하였을 때, 사용자중심 인터페이스가 모든 팔동작에서 빠른 응시시간을 보였지만, 팔동작에 따라 반응시간은 차이를 보였다. 그리고 정확도는 유의하지 않는 결과를 나타냈다. 실험 2에서는 텍스트 자극이 가지고 있는 메시지의 복잡성을 제거한 심볼자극을 이용하여 실험을 진행하였다. 그 결과, 사용자 중심 인터페이스가 모든 팔동작에서 빠른 응시시간과 반응시간, 높은 정확도를 보였다.이를 통해 피험자의 팔동작에 따라 스마트워치 디스플레이가 회전하며 발생시키는 심적회전에 대한 노력을, 사용자 중심 인터페이스가 줄여주면서 기존 인터페이스와 비교하여 정보 가독성에 긍정적인 영향을 미친다는 것을 확인하였다. 결론에서는 실험 1과 실험 2의 결과를 바탕으로 연구에 대한 한계점과 사용자 경험에 대한 실무적 시사점을 제시하였다.
Many people use smartwatches in diverse situations in everyday life including leisure time and work hours. Smartwatch represents not only time and date, but also many other types text and image information such as message, weather information and schedule. However, users frequently face problems when reading the information on smartwatch. While the smartwatch screen is fixed in one direction, hands are moving in all directions as users move, hold or control something. In addition, smartwatch is worn on our wrist and message is shown horizontally. For that reason, new demands are arising on the presentation of information in wearable computing. This paper introduces a egocentric smartwatch interface, which presents information on the screen following a user’ gaze direction. This core element comes from a consideration of human factor: when people are looking at rotated sentences, they would spend a lot of attention resources for relocating and understanding the meaning. Previous research on egocentric interface is diverse and growing in the HCI research area. Especially, the effect of egocentric interface for navigating a map has been studied a lot. Hermann reported that an egocentric map oriented by user direction supported the navigation best, having achieved good results in navigation efficiency. Similarly, an egocentric design of maps, which is suitable for personalized, mobile context. Also, an egocentric perspective of maps is suitable for pedestrians. Furthermore, an egocentric viewpoint of navigation on large displays enhanced the performance of user''s navigation. Likewise, we applied an egocentric interface to smartwatches in order to make it easy for users to notice information even in complex situations and to reduce attentional cost caused by mental rotation. Shepard and Metzler reported that people have an ability called “mental rotation”, which means rotating objects in their mind. According to Nunez-Pena and Aznar-Casanova study, people have mental rotation abilities with which they can imagine changeable aspects of objects in their mind. They said that mental rotation is a “classical psychological process”, which has been behaviorally and psychophysically proven in previous studies. Here, we redefine the egocentric interface as a way of presenting information according to user''s viewing angle. It is expected that this interface would increase the usability of smartwatch by reducing cognitive overload. For this study, it was assumed that egocentric interface rotation would influence usability. To test this, we developed a prototype of egocentric interface using Moto360 smartwatch. To prove our hypothesis, we compared the cognitive difference between the newly proposed egocentric interface and existing, non-egocentric interface, thereby investigating the effect of egocentric watch. For the measurement of cognitive overload, attention time and performance time were chosen because when reading the information on smartwatch in real life, user first needs to comprehend the message, which is represented by the attention time, and do certain tasks, measured by performance time. For the experiment, we used a commercial mobile eye-tracker to track and measure quantitative behavioral data in a natural context. In this study, we defined egocentric interface as user-centric environment that changes according to the direction of user’s movement. The current study showed that the egocentric interface could be beneficial for smartwatch users. The implication of this study is that the value of a smartwatch depends on not only the features of the interface itself, but also the interaction created via the rotating contents that consider the user’s gaze direction. By carrying out this study, we could closely examine the difference in usability between egocentric and non-egocentric interface in the smartwatch. There is a need for future studies to extend the current study to explore egocentric interface in a more real-life context taking into account diverse attributes of human factors such as viewing angles and user context.
