The aim of the Previewing Information Operation (PIO) approach is to tackle some overhead factors imposed on the user-hypertext interaction. The purpose is to diminish cognitive overhead and disorientation problems by reducing some of their causes.

This paper describes an experiment carried out to evaluate the usability of the operations based on the PIO approach. Results from between-groups studies show that subjects' evaluation of the ease of use of the system and feeling of general orientation were affected by the presence of PIO operations. A further study has revealed that the PIO operations were predicted by standard navigational operations.

Keywords: hypertext, link selection, previewing information, evaluation.

Introduction

When referring to a user's interaction with a hypertext system, the metaphor generally used in the literature is that the user navigates or browses through the information by selecting those links which are interesting.

In such a scenario, an interactive session could be described as a sequence of link selections along with other navigational operations, as for instance backtracking and string searching. Each of the link selection operations performed is a very important unit of the navigation sequence the user goes through: without the link options and the navigation taking place by the user freely choosing among links, there is no hypertext.

Accordingly, the secondary navigational modes such as bookmarks, history lists, backtracking and search operations (Bernstein & Joyce, 1992), are probably as important as the link selection alternatives. Firstly, they promote the understanding of the embedded hypertext structure and the building of a cognitive map. Secondly, they help users orientate themselves when they are lost.