Usability Heuristics: Friend or Foe in Maritime Navigation Instrument Design?
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2011
The sphere of maritime navigation instruments is regulated by a comprehensive set of standards, including the RADAR and ECDIS performance standards issued by the IMO, and their corresponding IEC test standards. This complex of standards serves to provide a baseline for the minimum performance of the instruments in question, aimed towards ensuring that the mariner is suitably equipped to support the tasks associated with the navigation of the ship. In other terms, the IMO performance standards are conceived with a view towards ensuring that the navigation instruments are effective, efficient and satisfactory to use, which fundamentally makes them a collection of usability requirements standards. From this vantage point, especially MSC.191(79) is noteworthy: These performance standards cater for the harmonization of the presentation of navigation-related information on the bridge of a ship, the explicit purpose being to ensure that all navigation displays adopt a consistent human machine interface philosophy and implementation. It is of significance that not only does MSC.191(79) supersede the performance standards for individual equipment, it also extends beyond the main navigation instruments and covers the presentation of navigation-related information by equipment for which no performance standards have been adopted. The clear intention is to provide a complete bridge working environment with good interaction qualities.
The means towards this aim is arguably a set of usability heuristics, or rules of thump, described in the IMO performance standards and, often in greater detail, in the corresponding IEC test standards. Usability heuristics are however open-ended, for which reason the assessment of compliance is not a simple, binary issue. Given such circumstances, the assessment framework must be stringent; conversely, the outcome of usability evaluations will be difficult to predict, judge and compare.
Through analysis of the performance and test standards, we find that the usability heuristics contained in IEC 62288 undoubtedly addresses important usability aspects, and expectedly leads to improved usability of maritime navigational information systems. We however also find that important usability aspects such as good feedback, effective error prevention, easy error recovery, reduction of the user’s memory load and keeping the user in contro are absent from the usability requirements. Furthermore, it is found that the ‘Observation’ usability inspection method prescribed by IEC 62288 may be suboptimal for evaluation of task-related, context-dependent issues, whereas the usability inspection methods of Cognitive Walkthrough and Formal Usability Inspection may be more appropriate.
It is furthermore suggested to augment the IEC 62288 test standards with guidance on the number of usability inspectors required, their required knowledge of the domain and context-of-use, and their human factors skill-sets. As an alternative it is suggested that the inspection of evidence pertaining to usability work and testing performed by the navigational information display manufacturers may be an appropriate substitute for direct evaluation.
It is finally recommended to observe that usability inspection methods never were intended as a full-blown methodology, but as a part of one which also comprises user testing. In recognition, it is proposed that user testing becomes a mandatory part of the rule-base for the assessment of maritime navigational information displays.