Umesh Rajashekar, Lawrence K. Cormack, Alan C. BovikDiscrimination Images at the Fixation Point in Visual Search |
What draws the eye? Since the human visual system is foveated, there is something of an chicken-and-egg-problem concerning how we decide where to look when we shift our gaze about the world. We don’t want to waste energy looking at uninteresting or uninformative things, yet how do we know what would be useful to look at before we look at it? To answer this question, we have been using a modified version of the discrimination image paradigm of Beard and Ahumada (1998) combined with accurate eye-movement monitoring during visual search. The animated figure below illustrates the fundamental paradigm. A subject searches for a target embedded in 1/f noise, in this case a 64-pixel-square black-over-white edge. The noise about each fixation point is sampled and averaged to form a discrimination image which can be thought of as the template for which the subject is actually searching. The panel on the left shows a simulated pattern of fixations (a “scanpath”) from a single trial. The two panels on the right show an actual evolving discrimination image in which each update represents the addition of ~100 trials. The upper-right panel shows the simple average and the lower figure shows pixels that are significantly above or below the mean at a 95% confidence level.
