Unintended effects: varying icon spacing changes users' visual search strategy

Users of modern GUIs routinely engage in visual searches for various control items, such as buttons and icons. Because this is so ubiquitous, it is important that the visual properties of user interfaces support such searches. The current research is aimed at deepening our understanding of how the visual spacing between icons affects visual search times. We constructed an experiment based on previous icon sets [8] where spacing between icons was systematically manipulated, and for which we had a computational cognitive model that predicted performance. In particular, the model predicted that larger spacing would lead to slower search times. While this prediction was borne out, there was an unanticipated finding: users in this new experiment were substantially slower than in previous similar experiments with smaller spacing. In fact, results from this new experiment were better fit with a model that employed a fundamentally different, and less efficient, search strategy. A second experiment was conducted to explicitly test the surprising result that this varied and larger icon spacing would lead to increased search times. Results were consistent with this hypothesis. These results imply that while small differences in visual layout may not intrinsically produce large differences in user performance, they may cause users to adopt suboptimal strategies that do produce such differences.