Visual Search Processes Used in Map Reading

This paper discusses visual search theories that explain how humans search for objects on maps. A mapreading experiment considered variations in visual search processes ref ated to searching for targets with unique features and mrgets that share features with other objects. Experimental objects differing in colour, shape, size, and orientation were constructed. The importance of these characteristics was evaluated, as was the effect of the location of the target on the map. The time needed to find a target in a display and the proportion of incorrect decisions were measures of efficiency in spatialsearch studies. The most efficient spatial searches occur when targeu 'pop out' of the map. These searches use parallel processes and are indicated bv reaction times being independent of the number of symbols on the map. 'Pop-out' effecu occur when targets have some unique charact~ristics that distinguish them from other symbols. Results indicated that 'pop-out' effects could he produced by colour differences between targets and distractor symbols, or by differences that combined colour with other dimensions. The location of the target on the map also had a significant effect on reaction time. This could be partially explained by the size of the map relative to people's fields of vision.