Pre-Attentive Features

Much experimentation has been performed to determine the types of items are pre-attentively processed. Under experimental conditions, a feature is considered pre-attentively processed if it can be recognized within a set of "distractors" in less than 10 milleseconds. Non-preattentively processed items take 40 milleseconds per item or more. Pre-attentively processed features can be used in display design when we want the user to instantly (at a glance) extract information. (Figures adapted from Colin Ware's web-posted lecture slides, Data Visualization Lab, University of New Hamphsire.)

Summetry - Symmetrical lines tend to be perceived as a unit. The non-symmetrical line "pops-out."
Color - Color difference can make an item "pop-out" from surrounding items.
Size - Size is easily pre-attentively processed.
Shape - A difference in shape can be used to draw attention to an item.