Visual conspicuity and directed attention

In a previous paper (Engel, 1969) a method has been proposed for measuring the visual conspicuity of an object in its background. Associated with each object was a conspicuity area, defined as the retinal area within which the object to be looked for is seen during a short presentation. The size of this area was assumed to be a measure of an object factor called visual conspicuity. If the subject was informed about the retinal location of the test object with respect to the fixation point before each exposure, the object was correctly seen in a greater area, which was called visibility area. The difference in area illustrated the influence of preknowledge, a subject factor, on the results obtained. We have now investigated more closely how retinal areas within which the test object is seen, are influenced by directed attention due to expectation concerning the test object location. In the experimental set-up the subject was instructed to locate the tachistoscopically presented test object, while fixating a "fixation point" in the centre of the tachistoscope field. In addition, before each exposure a so-called "attention point" in a chosen fixed location in the tachistoscopic rest field was supplied. There was a high probability that the test object appeared indeed at the attention point, which helped the subject to direct his attention to the attention point while fixating the fixation point. The areas obtained under these circumstances were called "attention areas" and will be shown to link the conspicuity area with the corresponding visibility area.