App icon similarity and its impact on visual search efficiency on mobile touch devices

Users of mobile touch devices are often confronted with a great number of apps, challenging an efficient access to single applications. Especially when looking for infrequently used apps, users have to perform a visual search. We address this problem in two studies by applying knowledge about visual search efficiency to app icons on mobile touch devices. We aimed to transfer findings of similarity grouping for complex stimuli to a more applied setting and to investigate the effect of search efficiency on user experience. In Study 1 (N=18), we varied set size and target presence as well as visual similarity between icons by color manipulation. Results indicated a highly efficient search when the target was easy to discriminate from the distractors and a less efficient search with increasing similarity. These results were replicated in a second, more realistic use case (N=36). Regarding user experience, Study 2 showed that perceived usability and intuitiveness increased with search efficiency but that the overall liking also depended on the visual variety of the design. Moreover, although participants showed a general interest in a system supporting their search, most participants had concerns about data privacy with such a system. In conclusion, the results indicate that concepts and findings from basic attention research serve as fruitful heuristics for searches in more realistic (applied) settings. Furthermore, results showed that similarity manipulation with color works without controlling for other icon characteristics (e.g. luminance, shade). The findings might offer a new approach when designing for smooth interaction with mobile touch devices.