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An eye tracking methodology can help uncover subtle cognitive processing stages that are otherwise difficult to observe in visualization evaluation studies. Pros and cons of eye tracking methods are discussed here, including common analysis metrics. One example metric is the initial time at which all elements of a visualization that are required to complete a task have been viewed. An illustrative eye tracking study was conducted to compare how radial and linear graphs support value lookup tasks for both one and two data-dimensions. Linear and radial versions of bar, line, area, and scatter graphs were presented to 32 participants, who each completed a counterbalanced series of tasks. Tasks were completed more quickly on linear graphs than on those with a radial layout. Scanpath analysis revealed that a three-stage processing model was supported: (1) find desired data dimension, (2) find its datapoint, and (3) map the datapoint to its value. Mapping a datapoint to its value was slower on radial than linear graphs, probably because eyes need to follow a circular, as opposed to a linear path. Finding a datapoint within a dimension was harder using line and area graphs than bar and scatter graphs, possibly due to visual confusion of the line representing a data series. Although few errors were made, eye tracking was also used here to classify error strategies. As a result of these analyses, guidelines are proposed for the design of radial and linear graphs.

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Plasma Posters are large screen, digital, interactive posterboards situated in public spaces, designed to facilitate informal content sharing within teams, groups, organizations and communities. While interest in interactive community poster boards has grown recently, few successful examples have been reported. In this paper we describe an ongoing installation of Plasma Posters within our organization, and report qualitative and quantitative data from 20 months of use showing the Posters have become an integral part of information sharing, complementing email and Web-based sharing. Success factors include our design process, the reliability and flexibility of the technology and the social setting of our organization. We briefly describe three external installations of the Plasma Poster Network in public places. We then reflect on content posting as "information staging" and the ways in which the public space itself becomes part of the "interface" to content.