Last summer software designer Aubrey Johnson published a post on Medium with a specific critique of Apple’s brand new mobile operating system, iOS7. Johnson suggested that Apple’s new “hollow” icons, being more visually complex than “solid” icons, create cognitive fatigue for users that will eventually lead them to tire of the interface and stop using it. The timely, bite-sized post was shared and discussed widely, with some designers affirming it as sensible advice and others criticizing it as overblown, oversimplified, and lacking valid evidence.
An example of solid and hollow icons in the tab bar of an app in Apple’s iOS7. The selected icon, Top Charts, uses a filled-in "solid" style. The unselected icons use an outlined "hollow" style.
As a graduate student in human-computer interaction and a UX intern at Viget, I saw an interesting opportunity to test Johnson's claim with evidence from real users. To find a definitive answer to the question of whether hollow icons require more cognitive effort for users, I created a web app that measures users’ speed and accuracy in selecting icons with different visual styles. By studying the data from more than a thousand test participants, I found that hollow icons are not necessarily less usable than their solid counterparts. However, the results are actually a bit more complicated.