Effects of task load on continuous visual search

One of the standard observations with the continuous visual search task is that the subject will frequently detect the target prior to scanning the ro w of the search list that contains it. This indicates that the subject can detect the target not only within the row actually being scanned but, rathe r, within a somewhat larger field around the fixation location (detection f ield). First, we outline the results of some previous experiments in which we studied how the size of detection fields depends on task difficulty. In the first set of experiments task difficulty was increased by means of an i ncrease in visual load. In the second set it was increased by means of a no n-visual secondary task administered in addition to the search task. Second , we consider two models that can account for the results of these experime nts. Third, we then discuss an experiment that was conducted in order to te st the two models against each other. We shall come up with the conclusion that the size of detection fields depends on an attentional operation that specifies the locations of the display from which information gets processe d.