Categorization costs for hierarchical keyboard commands

Previous research comparing methods of issuing commands found that selecting a toolbar item is faster than selecting an item from two menus with either a mouse or keyboard shortcut. Over the course of 90 trials, however, the keyboard method showed the most improvement, nearing the toolbar response time. The study presented in this paper compared the response time of the keyboard method across 240 trials when items were drawn from a single versus two menus. Throughout the trials, the 1-menu condition produced selection times that were on average 600 ms to 800 ms faster than the 2-menu condition suggesting users in the 2-menu condition were not able to bypass the menu decision by chunking the 3-key sequence into one cognitive unit. Models are presented to describe performance at various stages of learning. Practical implications are that hierarchical, category-based keyboard commands do not provide a clear advantage to toolbar-based selection and that theory-based evaluation methods may need to reflect this result.