Eye tracking for visualization evaluation: Reading values on linear versus radial graphs

Abstract

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.

Star and polyline glyphs in a grid plot and on a map display: which perform better?

“…910 However, if comparisons are made among glyphs or if a compact area of glyphs is found with glyphs that are similar to each other, then star glyphs work better. These findings confirm, to some extent, those reported by Goldberg and Helfman (2011). Indeed, linear graphs 915 support the dimension-finding task better than do radial graphs.…”

“…By contrast, radial encoding of time in star glyphs works better if one has to find a particular temporal location. These findings contradict to some 215 extent Goldberg and Helfman (2011) claim that linear graphs can better support the dimension-finding phase, since their linearly aligned dimensions support searches better than radial graphs. Lee, Reilly, and Butavicius (2003) compare four visualization techni-220 ques, including Chernoff faces and star glyphs, in terms of their usefulness in user tasks.…”

“…One of the most commonly used glyph types is star glyphs. Although they have been 35 implemented in many geovisualization environments (Gribov et al, 2006;Takatsuka & Gahegan, 2002), their use is impeded by polar coordinates in which visual scanning is more time-consuming and more error-prone than reading vertical and horizontal axes 40 (Goldberg & Helfman, 2011). Therefore, Opach and Rød (2017) propose the use of polyline glyphs that resemble polylines from parallel coordinates as an alternative to star glyphs.…”

“…Since parallel coordinates are aligned in the polyline glyphs, users may find it easier to get datapoint values than with star glyphs, in which polar coordinates are used. Goldberg and Helfman's (2011) eye-tracking study revealed that 195 visual scanning can be done more quickly along vertical and horizontal axes than circular scanning along rings, and the latter method is error-prone and not reliable. However, since star glyphs are more centered and compacted than polyline glyphs, they 200 might perform better in tasks involving either similar or distinctive glyphs.…”

“…According to Goldberg and Helfman (2011), to date, this technique has been underutilized as a method for understanding how individuals make use of information 235 graphics. Although there has been a rapid increase in eye-tracking studies in geovisualization, studies of glyph-based visualization have been sparse and seldom.…”