A Predictive Model of Human Performance With Scrolling and Hierarchical Lists

ABSTRACT

Many interactive tasks in graphical user interfaces involve finding an item in a list but with the item not currently in sight. The two main ways of bringing the item into view are scrolling of one-dimensional lists and expansion of a level in a hierarchical list. Examples include selecting items in hierarchical menus and navigating through “tree” browsers to find files, folders, commands, or e-mail messages. System designers are often responsible for the structure and layout of these components, yet prior research provides conflicting results on how different structures and layouts affect user performance. For example, empirical research disagrees on whether the time to acquire targets in a scrolling list increases linearly or logarithmically with the length of the list; similarly, experiments have produced conflicting results for the comparative efficacy of “broad and shallow” versus “narrow and deep” hierarchical structures. In this article we continue in the human–computer interaction tradition of bringing theory to the debate, demonstrating that prior results regarding scrolling and hierarchical navigation are theoretically predictable and that the divergent results can be explained by the impact of the dataset's organization and the user's familiarity with the dataset. We argue and demonstrate that when users can anticipate the location of items in the list, the time to acquire them is best modeled by functions that are logarithmic with list length and that linear models arise when anticipation cannot be used. We then propose a formal model of item selection from hierarchical lists, which we validate by comparing its predictions with empirical data from prior studies and from our own. The model also accounts for the transition from novice to expert behavior with different datasets.     

Safety-critical Java programs from Circus models

Safety-Critical Java (SCJ) is a novel version of Java that addresses issues related to real-time programming and certification of safety-critical applications. In this paper, we propose a technique that reveals the issues involved in the formal verification of an SCJ program, and provides guidelines for tackling them in a refinement-based approach. It is based on Circus, a combination of well established notations: Z, CSP, Timed CSP, and object orientation. We cater for the specification of timing requirements and their decomposition towards the structure of missions and event handlers of SCJ. We also consider the integrated refinement of value-based specifications into class-based designs using SCJ scoped memory areas. We present a refinement strategy, a Circus variant that captures the essence of the SCJ paradigm, and a substantial example based approach on a concurrent version of a case study that has been used as a benchmark by the SCJ community: an aircraft collision detector.     

The Safety-Critical Java memory model formalised

Safety-Critical Java (SCJ) is a version of Java for real-time programming, restricted to facilitate certification of implementations of safety-critical systems. Its development is the result of an international effort involving experts from industry and academia. What we provide here is, as far as we know, the first formalisation of the SCJ model of memory regions. We use Hoare and He’s unifying theories of programming (UTP), enabling the integration of our theory with refinement models for object orientation and concurrency. In developing the SCJ theory, we also make a contribution to UTP by providing a general theory of invariants (an instance of which is used in the SCJ theory). The results presented here are a first essential ingredient to formalise the novel programming paradigm embedded in SCJ, and enable the justification and development of formal reasoning techniques based on refinement.     

Hi-trees and their layout

We introduce hi-trees, a new visual representation for hierarchical data in which, depending on the kind of parent node, the child relationship is represented using either containment or links. We give a drawing convention for hi-trees based on the standard layered drawing convention for rooted trees, then show how to extend standard bottom-up tree layout algorithms to draw hi-trees in this convention. We also explore a number of other more compact layout styles for layout of larger hi-trees and give algorithms for computing these. Finally, we describe two applications of hi-trees: argument mapping and business decision support.     

Superpositional connectionism: A reply to Marinov

Marinov's critique I argue, is vitiated by its failure to recognize the distinctive role of superposition within the distributed connectionist paradigm. The use of so-called subsymbolic distributed encodings alone is not, I agree, enough to justify treating distributed connectionism as a distinctive approach. It has always been clear that microfeatural decomposition is both possible and actual within the confines of recognizably classical approaches. When such approaches also involve statistically-driven learning algorithms — as in the case of ID3 — the fundamental differences become even harder to spot. To see them, it is necessary to consider not just the nature of an acquired input-output function but the nature of the representational scheme underlying it. Differences between such schemes make themselves best felt outside the domain of immediate problem solving. It is in the more extended contexts of performance DURING learning and cognitive change as a result of SUBSEQUENT training on new tasks (or simultaneous training on several tasks) that the effects of superpositional storage techniques come to the fore. I conclude that subsymbols, distribution and statistically driven learning alone are indeed not of the essence. But connectionism is not just about subsymbols and distribution. It is about the generation of whole subsymbol SYSTEMS in which multiple distributed representations are created and superposed.Some of the material in sections 2 and 3 is drawn from Clark, A., ASSOCIATIVE ENGINES: CONNECTIONISM, CONCEPTS AND REPRESENTATIONAL CHANGE (Cambridge, MA MIT/Bradford Books, forthcoming 1993). Thanks to the publishers for permission to reproduce that material here. Thanks also to Chris Thornton for an illuminating discussion of ID3.     

Development of an Apparatus for pH-Isolated Electrokinetic In Situ Chemical Oxidation

An apparatus was designed, manufactured, and implemented to isolate pH during electrokinetic in situ chemical oxidation (EK-ISCO). H+ and OH- electromigration were used to determine the adequacy of the designed apparatus for pH isolation. A series of pH-isolation and normal-mode (no pH-isolation) experiments were undertaken and compared. It was found that pH isolation was achieved when the electrode reservoirs were separated by porous media combined with the purging of the electrode reservoir fluid. The electromigration retardation factor of H+ and OH- was calculated for the porous media using the observed pH breakthrough times. The retardation factor for H+ was also calculated by considering mass flux data. The retardation factors for H+ and OH- were found to be 28.3 and 95, respectively, when using the breakthrough time. The retardation factor for H+ was calculated to be 36.7 using the mass flux data.     

Rate of change of composition of lettuce in response to nitrogen depletion or re‐supply

BACKGROUND: Lettuce accumulates high levels of nitrate when grown in winter in heated greenhouses. Temporarily removing nitrate from the nutrient solution may lower tissue nitrate. The composition of hydroponic lettuce was examined over a 6‐ to 13‐day interval of nitrogen depletion or re‐supply. RESULTS: Growth responses were delayed by 6 days or more after changing N supply, except root growth responded in 3–4 days. The total nitrogen increased or decreased for 6 days. When measured in the light, nitrate concentration changed 10‐fold in roots within 2 days. The change in leaf and petiole tissue was slower. Amino acids responded to a change in N‐supply within 1 day in leaf and root. All tissues of N‐depleted plants had more sugars compared to N‐sufficient plants within 2 days after the start of depletion. Nitrogen depletion had reversible effects on growth or tissue concentrations if applied for only 6 days. CONCLUSIONS: Tissue nitrate changed more rapidly than total nitrogen, or growth responses. However, nitrate changed more slowly in petiole than in leaf blade or roots, and larger plants have more biomass in petioles. Thus, clearing nitrate from lettuce is slower for large compared to smaller lettuce plants. Copyright © 2012 Society of Chemical Industry     

A Triangular Double Cantilever Beam Test for Measuring Adhesive or Cohesive Fracture Energy

A thin layer of adhesive bonded between two stiff elastic plates of uniform thickness and triangular in shape is recommended as a test specimen for measuring cohesive or adhesive strength. A similar test was employed many years ago by Mostovoy et al. ^1,2 but appears to have received little attention in the intervening period. Nevertheless, it has marked advantages in comparison with current ASTM tests in simplicity of construction and use. Examples are given using silicone rubber layers bonded between steel plates.