Color and Visual Search in Large and Small Display Fields

In previous experiments we have attempted to measure color differences required to obtain parallel visual search. (Nagy and Sanchez, 1988) The observer's task was to search for a small target disk that differed only in color from white distractor disks also present in the display. When the color difference between the target and distractors was small the time required to find the target depended on the number of distractors present. We refer to this as a serial search. When the color difference was large the search time was independent of the number of distractors present. We refer to this as parallel search. In order to estimate the color difference required to obtain parallel search we measured search time as a function of color difference in displays with a large number of distractors. Search times decreased with increases in color difference until a minimum was reached and then remained constant with further increases in color difference. From these experiments we estimated the smallest color difference at which parallel search could be obtained along several lines in color space. We will refer to these color differences as critical color differences, or CCD's. CCD's varied from approximately 12 to 40 times the size of the MacAdam unit of color difference depending on the direction in color space.