Effects of secondary tasks on search performance

Summary Two experiments studied the effect of secondary task load on continuous visual search. Two effects were observed when a secondary task was applied. Search speed (which is assumed to reflect the efficiency of nontarget rejection) was impaired, whereas target detection distance (which presumably reflects the efficiency of target detection) increased. These findings are explained in the framework of a two-process model of visual search which assumes that two operations are performed simultaneously during each fixation, that is, automatic detection and controlled search. The secondary task interferes with the operation of controlled search which reacts to this impairment by way of a compensatory slow-down of search speed. This gain in time also benefits the operation of automatic detection which converts the temporal gain into a spatial extension of the area under its control.