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.
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'.