Some questions of hypermedia and CHI Josep Blat Universitat Pompeu Fabra

Some aspects of human-computer interaction and hypermedia General question: Human information processing based models (GOMS, for example) Experimental evaluation is a must Complexity of developing successful hypermedia

GOMS, Human Information Processing GOMS (Card, Moran, Newell) stands for Goals, Operators, Methods, Selection rules GOMS tries to predict performance (and usability problems) when using computer systems Based on an Applied Psychology model of the Human Information Processor The HIP is composed of perceptual, motor and cognitive systems (and corresponding perceptual and cognitive memories, which can be short term or long term)

Example of GOMS application The keystroke level model based on GOMS tries to predict performance when using a text editing system Methods for this model are keystroking, pointing with a mouse, returning the hands to ‘home’, drawing a specific line, mental preparation, response by system Operators in this model are sequences of methods allowing to perform a small unit-task

Example of GOMS application 2 Parameters can be estimated and performance predicted using some laws For instance, Fitts’ law for time T required to point with the mouse depends on size S of the object, of distance D as T = log (D/S+.5); it is based on the model of HIP Constants were experimentally obtained Experimental validation of predictions can be carried out

More general GOMS analysis Hierarchical decomposition and analysis of tasks can be performed, in general, using GOMS at different levels of granularity We can compare different interfaces when performing specific tasks (or alternative methods which can be selected when using an interface) There are other models refining this one, and taking into account semantic, and syntactic aspects allowing for analysis of interfaces

Concluding about GOMS Use Applied Psychology models of human information processing Develop task analysis, and performance models Predict and evaluate (time) performance GOMS is a relevant model

Experimental evaluation Under GOMS, experiments can be used to evaluate prediction (and hence, predict performance) General experimental evaluation is a must for a user-oriented approach Example: Evaluating experimentally whether hypertext browsing is better than using standard (paper based) documentation

Evaluating hypertext vs traditional documentation Ask specific items for evaluation such as: –Searching fixed questions –Writing essays –Recalling incidental information Also ask about subjective rating

Evaluating hypertext vs traditional documentation 2 Experimental results (1989) using Superbook showed superiority: –In accuracy when searching three out of four fixed questions, especially when questions not clearly in documentation headings, … –When writing open book essays by students –Recalling some incidental information Subjective rating gave also advantage to Superbook Seemingly, hypertext allows for better performance in non-standard cases

Concluding about experimental evaluation of hypertext Experimental evaluation is a must for user- centred approach Evaluation must be done with precise questions But also subjective rating is interesting Understand hypertext advantages with respect to text

Seven barriers to successful hypermedia development Glushko (1992) quotes seven pitfalls: –Realistic expectations –Multidisciplinary project team –Establishing and following design guidelines –Dealing with installed base constraints –Obtaining usable source files –Finding appropriate software technologies and methods –Legal uncertainties wrt intellectual property concerns Good commercial hypertext is hard to develop

Some references Ronald M Baecker et al: Readings in Human-Computer Interaction (Toward the Year 2000), Morgan Kauffman, Chapters 9 and 13. Stuart K. Card, Thomas P. Moran, Allen Newell: The Psychology of Human- Computer Interaction, Lawrence Erlbaum Associates, 1983.