Abstract
Usability of tree-structured menu retrieval systems on depth/breadth trade-off is investigated. A user model on menu retrieval behaviour was proposed, which classifies retrieval time into three categories as visual search on a menu, judgement whether the menu item includes the goal, and keying operation. Based on this model, changes of these times were theoretically discussed in relation with learning phenomenon of users, and such tendencies were forecasted that when the menu structure become deeper, the more retrieval time is to be required to reach the goal. Experiments was conducted to examine the change of goal acquisition speed in accordance with learning, and the results which support the forecasts were obtained. In addition, the experiment showed that names of menu items were of importance for usability because names of menu items act as representation of goals in the cognitive ergonomic sense. Besed on these results, several ergonomic guidlines for tree-structured menu retrieval systems were proposed as the conclusion in this study.
