Demonstrating set size effects in the absence of Visual search
A cornerstone finding in the Visual search literature is that search times increase with the number of items appearing in a display. This "set size" effect is believed to result from an attentional process moving from one display item to the next in search of the target. On average, the more items there are in a display, the more movements will be required to find the target, resulting in a set size effect. According to this simple model of search, if an observer already knew the location of the target in the display, then only a single movement would be required regardless of the actual number of display items. This hypothesis was tested and a set size effect was observed even in the absence of Visual search (Zelinsky, 1999d). This finding challenges the widely held assumption that target spatial uncertainty is the sole factor determining set size effects in a search task. Ongoing work is attempting to parameterize this finding and offer a theoretical explanation (Zelinsky, 2000c, 2001a).
Research Philosophy
Each time we engage in a moderately complex task, we likely enlist the help of an untold number of simpler visuo-motor operations that exist largely outside of our conscious awareness. Consider for instance the steps involved in preparing a cup of coffee. For the sake of simplicity, assume that the coffee has already been brewed and is waiting in the pot, and that all of the essential accessories, an empty cup, a spoon, a carton of
cream, and a tin of sugar, are sitting on a countertop in front of you. What is your first step toward accomplishing this goal? The very first thing that you might do is to move your eyes to the handle of the coffee pot, followed shortly thereafter by the much slower movement of your preferred hand to the same target. Because the coffee pot is hot and the handle is relatively small, this change in fixation is needed to guide your hand to a safe and useful place in which to grasp the object. After lifting the pot, your eye may then dart over to the cup. This action is needed, not only to again guide the pot to a very specific point in space directly over the cup, but also to provide feedback to the pouring operation so as to avoid a spill. After sitting the pot back on the counter (an act that may or may not require another eye movement), your gaze will likely shift to the spoon. Lagging shortly behind this behavior may be simultaneous movements of your hands, with your dominant hand moving toward the sugar tin and your non-preferred hand moving to the spoon. The spoon is a relatively small and slender object that again requires assistance from foveal vision for grasping; the tin is a rather bulky and indelicate object that does not require precise Visual information to inform the grasping operation. Once the spoon is in hand and the lid to the tin is lifted, gaze can then be directed to the tin in order to help scoop out the correct measure of sugar. To ensure that the spoon is kept level, a tracking operation may be used to keep your gaze on the loaded spoon as it moves slowly to the cup. After receiving the sugar, and following a few quick turns of the spoon, your coffee would finally be ready to drink (see Land et al., 1998, for a similarly framed example).
eye movements and visual cognition