Abstract
Image a situation in which two uniquely colored and highly distinguishable objects are present in the visual field. Each time before you start searching, you are told which of the two objects you need to select. For example, on one trial you need to select the red object and on the next trial you need to select the green one. On the face of it, this should be no problem: Everyone expects that people can select the object they are told to select. This intuitive assumption is reinforced by basically all theories on visual search which predict that people can select the object needed for their task. The basic idea is that top-down set can increase the salience of the relevant feature dimension (in this example: the feature “red” or “green”) such that attention is guided to the relevant feature only Even though all theories predict efficient top-down selection, here we show that selection in a top-down manner is inefficient; people cannot flexibly select the object needed for their task. Observers viewed displays in which two equally salient color singletons were simultaneously present. Before each trial, observers received a word cue (e.g., the word ‘red’, or ‘green’) telling them which color singleton to select on the upcoming trial. The results show that selection was not perfect: When searching for the relevant color, observers could not prevent attentional capture by the irrelevant color singleton. Only when the color of the target singleton remained the same from one trial to the next was selection perfect, an effect which is thought to be the result of passive automatic intertrial priming. The present study demonstrates the limits of top-down attentional control.