Balancing search and retrieval in hypertext: context-specific trade-offs in navigational tool use
We compare user navigation performance using two hypertext information sites of identical node structure but embedded in different metaphors. The first is based upon the layout of a house and is consistent with Euclidean space. The second represents social links between people for which a spatial metaphor is not apparent. Search for targets within the structures, and the speed of their subsequent retrieval on a second search, is compared in a 242 factorial design manipulating: metaphor (spatial or non-spatial); navigation tools (participants have both a site map and bookmark tool, one of these, or no tools at all) and the time pressure under which navigation is carried out (paced or unpaced). A strong main effect is found in which the spatial metaphor produces higher performance under all conditions. Similarly, time pressure has the general effect of trading-off a faster initial search with less efficient retrieval later. However, navigation tool use is highly context dependent and sometimes counterintuitive: certain conditions show poorer performance with two navigation aids than one. We argue that navigation tools are mediating structures for activities, such as bookmarking and learning the structure of the site, which represent cognitive investment for future retrieval. In this view, user performance is optimized by the balance of two potentially antagonistic conditions. First, the usability of tools and metaphor must free cognitive resources for planning; but also, the difficulty of the task and the need for planning must remain visible to the user. The implications for design are discussed.
navigation spatial metaphor memorability www