ABSTRACT

Humans spend a lot of time searching for things, such as roadside traffic signs, soccer balls, or tumors in mammograms. These tasks involve the deployment of attention from one item in the visual field to the next. Common sense suggests that rejected items should be noted in some fashion so that effort is not expended reexamining items that have been attended and rejected. However, common sense is wrong. We had human observers search for a letter "T" among letters "L". This search demands visual attention and normally proceeds at the cost of 20-30 milliseconds per item. In the critical condition, we randomly relocated all letters every 111 msec. This made it impossible to keep track of the progress of the search. Nevertheless, the efficiency of the search was unchanged. Theories of visual search have uniformly assumed that search relies on accumulating information about the identity of objects over time^,,. Such theories must predict that search efficiency will be drastically reduced if the scene is continually shuffled while the observer is trying to search through it. Since efficiency is not impaired, the standard theories must be revised.