THE SCALE BANDWIDTH OF VISUAL-SEARCH

Observers were asked to locate a target in a brief, two-scale display. Accuracy of locating the target was measured as a function of the rat io between the two scales. At each scale ratio, the probability of loc ating the target as a function of the number of elements is well fit b y the idea that the observer accurately monitors only a ''critical'' n umber of elements. The dependence of critical number on scale ratio is well accounted for by a model that assumes that the observer's decisi on is based on an evenly spaced array of samples. The sample spacing i s under attentional control, but is always uniform.