The Effects of Menu Parallelism on Visual Search and Selection

Menus and toolbars are the primary controls for issuing commands in modern interfaces. As software systems continue to support increasingly large command sets, the user's task of locating the desired command control is progressively time consuming. Many factors influence a user's ability to visually search for and select a target in a set of menus or toolbars, one of which is the degree of parallelism in the display arrangement. A fully parallel layout will show all commands at once, allowing the user to visually scan all items without needing to manipulate the interface, but there is a risk that this will harm performance due to excessive visual clutter. At the other extreme, a fully serial display minimises visual clutter by displaying only one item at a time, but separate interface manipulations are necessary to display each item. This paper examines the effects of increasing the number of items displayed to users in menus through parallelism---displaying multiple menus simultaneously, spanning both horizontally and vertically---and compares it to traditional menus and pure serial display menus. We found that moving from serial to a partially parallel (traditional) menu significantly improved user performance, but moving from a partially parallel to a fully parallel menu design had more ambiguous results. The results have direct design implications for the layout of command interfaces.