Subjective Usability, Mental Workload Assessments and Their Impact on Objective Human Performance

Self-reporting procedures and inspection methods have been largely employed in the fields of interaction and web-design for assessing the usability of interfaces. However, there seems to be a propensity to ignore features related to end-users or the context of application during the usability assessment procedure. This research proposes the adoption of the construct of mental workload as an additional aid to inform interaction and web-design. A user-study has been performed in the context of human-web interaction. The main objective was to explore the relationship between the perception of usability of the interfaces of three popular web-sites and the mental workload imposed on end-users by a set of typical tasks executed over them. Usability scores computed employing the System Usability Scale were compared and related to the mental workload scores obtained employing the NASA Task Load Index and the Workload Profile self-reporting assessment procedures. Findings advise that perception of usability and subjective assessment of mental workload are two independent, not fully overlapping constructs. They measure two different aspects of the human-system interaction. This distinction enabled the demonstration of how these two constructs cab be jointly employed to better explain objective performance of end-users, a dimension of user experience, and informing interaction and web-design

An investigation into usability and exclusivity issues of digital programmable thermostats

This is the pre-print version of the Article - Copyright @ 2011 Taylor & FrancisWith nearly 60% of domestic energy consumption relating to space heating, the interaction between users and their heating controls is crucial in reducing consumption. Yet, many heating controls are complex and exclude people due to the demands placed upon their capabilities in terms of vision, reach, dexterity and thinking. This study explores the scale of and reasons for user exclusion in relation to digital programmable thermostats. The Exclusion Calculator was used to estimate the percentage of the population excluded from the use of three products. Full user testing was then conducted to elicit specific usability problems of the devices. The participants were a group of 14 younger users (aged 24–44) and 10 older users (aged 62–75). The exclusion calculations underestimated the actual exclusion significantly for both age ranges (p<0.05). None of the older users were able to complete the programming of the thermostats. Additionally, the cognitive demands of these systems were considered using a subjective workload assessment method, based on the NASA Task Load Index, and were found to be excessive. In conclusion, this study makes recommendations to facilitate the design of more inclusive digital programmable thermostats. It is argued that such changes could result in reductions in domestic heat energy consumption.This work is funded by the ESPRC and Buro Happold

Questioning conventions : are product conventions trading off the usability of products for short term user satisfaction

Mapping conventions are a key aspect of user centered design as they present users with familiar interactions in unfamiliar products. Conventions evolve over time and are slow to be adopted, requiring a high percentage of acceptance within a society, ensuring that conventions exhibit a sufficient level of usability. However this paper argues that while usability is a necessary condition for good interactions it is not a sufficient one. Therefore user centered design which accents individuals bias towards conventions my in fact be hindering the innovation of product interactions. This paper argues that a cognitive approach should be adopted in order understand and reassess product interactions. An experiment was carried out that demonstrates the influence that simple mappings can have on cognitive load. The results showed that basic mappings of the types that are found throughout product conventions can have a substantial impact on mental load and subsequently product interaction

Analyzing the Impact of Cognitive Load in Evaluating Gaze-based Typing

Gaze-based virtual keyboards provide an effective interface for text entry by eye movements. The efficiency and usability of these keyboards have traditionally been evaluated with conventional text entry performance measures such as words per minute, keystrokes per character, backspace usage, etc. However, in comparison to the traditional text entry approaches, gaze-based typing involves natural eye movements that are highly correlated with human brain cognition. Employing eye gaze as an input could lead to excessive mental demand, and in this work we argue the need to include cognitive load as an eye typing evaluation measure. We evaluate three variations of gaze-based virtual keyboards, which implement variable designs in terms of word suggestion positioning. The conventional text entry metrics indicate no significant difference in the performance of the different keyboard designs. However, STFT (Short-time Fourier Transform) based analysis of EEG signals indicate variances in the mental workload of participants while interacting with these designs. Moreover, the EEG analysis provides insights into the user's cognition variation for different typing phases and intervals, which should be considered in order to improve eye typing usability.Comment: 6 pages, 4 figures, IEEE CBMS 201

Acquiring Procedural Knowledge of a Technology Interface: Introduction to this Special Issue.

Guidelines and models for procedural instructions can be supported by three types of research. Careful analytical studies of collections of instructions can help to identify, describe, and evaluate strategies that writers and designers apply. Empirical studies measure the effects of document variables on the performance of users, thus offering evidence, contraevidence, or refinements for existing guidelines. Theoretical studies, finally, aim to describe and explain the behavior of readers of instructions. To designers and writers, they provide a deeper insight in the underlying cognitive processes that determine success or failure of their work. This special issue offers research articles in all three categories

The design and evaluation of an auditory-enhanced scrollbar

A structured method is described for the analysis of interactions to identify situations where hidden information may exist and where non-speech sound might be used to overcome the associated problems. Interactions are considered in terms of events, status and modes to find any hidden information. This is then categorised in terms of the feedback needed to present it. An auditory-enhanced scrollbar, based on the method described, was then experimentally tested. Timing and error rates were used along with subjective measures of workload. Results from the experiment show a significant reduction in time to complete one task, a decrease in the mental effort required and an overall preference for the auditory-enhanced scrollbar