Effect of linear magnification on target detection performance in visual inspection

This paper reports on an experiment on the effects of four levels of linear magnification (no scaling, 1.3 times scaling, 1.69 times scaling and 2.2 times scaling) on the detection of peripheral visual targets on four axes (eight meridians). Performance was measured by the linear dimensions of the sensitivity limit on a meridian (in deg) and by the number of locations at which targets were correctly detected within the two sensitivity limits on each axis. The sensitivity limit was defined as the farthest eccentricity at which 50% correct target detection was achieved. Detection performance with scaled stimuli was better than performance with non-scaled stimuli as shown by the increase in sensitivity limits with the increase in scaling. However, the number of targets correctly detected within the sensitivity limits was statistically equal for all the scaling levels. Enlarging object size at central locations to the same degree as those in the periphery yielded little benefit under the conditions of this experiment. For the conditions used here, this result indicated the ineffectiveness of scaling stimulus in the vicinity of fixation under linear magnification. The result emphasises the importance of selecting appropriate inter-object spacing as well as object size for displays designed to facilitate performance on visual search tasks. From an economic point of view, it seems to be wasteful to enlarge targets at the vicinity of fixation to the same degree as those at more eccentric locations.