How does knowing what you are looking for change visual search behavior?

When searching a display, users sometimes know what the target is but sometimes do not. It has generally been assumed that for this latter case people must engage in a deeper semantic evaluation of items during the search process. This idea is central to Information Foraging theory. But do people actually spend longer assessing items when engaged in a semantically demanding search task' We investigate this by having participants locate target items in 16-item menus. Participants were either told exactly what to look for (known-item search) or they were told the category that the target belonged to (semantic search). Participants were faster and more accurate at known-item searches. Eye-movement data show that this was because participants were more likely to skip over items when performing known-item searches. Contrary to expectation, we found limited empirical evidence to support the idea that deeper semantic evaluations of items lead to longer gaze durations (this occurred only when items were arranged very close together). This finding is important because it reveals how people adopt different eye gaze strategies depending on the kind of search activity they are engaged in.