People underestimate average positions of lines and overestimate bars.
“Perceptual pull” also diminishes or exaggerates the effect of underestimation and overestimation depending on the spatial arrangement of the data series.
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Information visualizations contain many perceivable patterns. Viewers must exercise top-down attentional control to extract a series of relationships and patterns from the data values.
Top-down cues (a verbal description of a particular pattern) can increase visual salience for that particular pattern, driving it so strongly that participants could not turn it 'off'.
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