What Do People See in a Twenty-Second Glimpse of Bivariate Vector Field Visualizations?

Little is known about how people learn from a brief glimpse of three-dimensional (3D) bivariate vector field visualizations and about how well visual features can guide behavior. Here we report empirical study results on the use of color, texture, and length to guide viewing of bivariate glyphs: these three visual features are mapped to the first integer variable (v1) and length to the second quantitative variable (v2). Participants performed two tasks within 20 seconds: (1) MAX: find the largest v2 when v1 is fixed; (2) SEARCH: find a specific bivariate variable shown on the screen in a vector field. Our first study with eighteen participants performing these tasks showed that the randomized vector positions, although they lessened viewers' ability to group vectors, did not reduce task accuracy compared to structured vector fields. This result may support that these color, texture, and length can provide to a certain degree, guide viewers' attention to task-relevant regions. The second study measured eye movement to quantify viewers' behaviors with three-errors (scanning, recognition, and decision errors) and one-behavior (refixation) metrics. Our results showed two dominant search strategies: drilling and scanning. Coloring tended to restrict eye movement to the task-relevant regions of interest, enabling drilling. Length tended to support scanners who quickly wandered around at different v1 levels. Drillers had significantly less errors than scanners and the error rates for color and texture were also lowest. And length had limited discrimination power than color and texture as a 3D visual guidance. Our experiment results may suggest that using categorical visual feature could help obtain the global structure of a vector field visualization. We provide the first benchmark of the attention cost of seeing a bivariate vector on average about 5 items per second.