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Objects and mappings: incompatible principles of display design--a critique of Marino and Mahan.

Article Excerpt
Mappings in Support of Integration Tasks

Representation aiding is a "problem-driven" or an "ecological" approach to display design with a general orientation that is consistent with cognitive systems engineering (Rasmussen, Pejtersen, & Goodstein, 1994). Effective decision support depends upon three system components: the domain (the work to be done), the agents (the humans or machines doing the work), and the interface between them (usually, but not necessarily, computerized). Each of these components contributes a set of constraints; the effectiveness of graphical decision support will ultimately depend upon the quality of very specific sets of mappings between these constraints (e.g., Bennett & Flach, 1992).

PCP is an alternative approach to display design with a distinctly different emphasis (Wickens & Carswell, 1995). Marino and Mahan's (2005) interpretation of PCP places a central role on perceptual "objects" (all italics added): "In object configural displays, multiple pieces of information are mapped to a single perceptual object" (p. 122). Objects are the primary consideration in the authors' definition of the core principle of display proximity: high display proximity occurs "[w]hen different features of the same object represent multiple pieces of information" (p. 122); low display proximity occurs "[w]hen separate perceptual objects ... represent multiple pieces of information" (p. 122). For tasks in which multiple pieces of information must be considered to reach a decision (high-proximity tasks), Marino and Mahan predict that high-proximity displays will facilitate performance: "high-proximity tasks should be best supported by high-proximity displays" (p. 122).

Over a decade ago Bennett and Flach (1992) reviewed the visual attention, object perception, and display design literatures with regard to the role that a perceptual object should play as a display design principle. They urged designers to reconsider the prominent role that was often conferred. Bennett and Flach (1992, p. 528) provided reasonably compelling evidence that "improved performance at integrated tasks is more closely tied to configural properties of visual forms ... than to objectness per se." (Note that the terms integrated tasks and high-proximity tasks are interchangeable for the purposes of this critique.) For example, it has been demonstrated that a nonobject display can produce significantly belier performance at integrated tasks than an object display can (Sanderson, Flach, Buttigieg, & Casey, 1989). The critical considerations are configurality (i.e., emergent features) and the degree to which the emergent features map into domain properties. Configural display formats will provide effective decision support for integrated tasks if "the display produces highly salient emergent features and these emergent features directly reflect the critical data relationships and inherent constraints in the domain" (Bennett & Flach, 1992, p. 530).

Marino and Mahan (2005) describe their working premise with regard to the critical data relationships in the domain of nutritional quality: "[T]here was general consensus among the subject-matter experts that nutritional quality reflects the balance between nutrients that need to be limited in the diet and those that need to be consumed in adequate amounts" (p. 126. italics added). The authors assume no interactions between nutrients and therefore adopt the design goal of developing a display that illustrates the difference in the overall quality of the nutrients between the two categories (i.e., limited and adequate).

For the moment this working...

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