ABSTRACT

The useful field of view is defined as the area around the fixation point from which information is being processed, in the sense of being stored or acted upon during a given visual task. The main question is: Why is this useful field of view or effective fixation area often limited in size, as compared with the physiologically possible field of view? Mackworth (1965) found useful fields of view reduced to 2° in tachistoscopic studies involving visual noise and small objects. Three letters were shown for 100 msec, and the distance between them was varied. Even at separations of 10° the subjects could easily compare the letters, but when extra "noise" letters were added to the same displays, the target letters had to be as close as 2° before they could be recognized. Even in a situation with only two dials, the subject could not detect an infrequent signal on one dial when he was looking at the other one, although the distance between the dial centers was only 6° (Mackworth, Kaplan, & Metlay, 1964).