Evidence for the pre-attentive state comes from Treisman's own studies. In a well-known study, Treisman created a display of four objects flanked by two black numbers. The display flashed on a computer screen for 1/5 of a second and followed by a random-dot masking field to eliminate residual perception of the stimuli after the stimuli were turned off. Participants were asked to first report on the black numbers, followed by what they saw at each of the four locations where the shapes had been. Under these conditions, participants reported seeing illusory conjunctions in 18% of trials. That is, participants reported seeing objects that consisted of a combination of features from two different stimuli. For example, after seeing a big yellow circle, a big blue triangle, a small red triangle, and a small green circle, a person might report seeing a small red circle and a small green triangle. The reason illusory conjunctions occurred is that stimuli were presented rapidly and the observers' attention was distracted from the target object by having them focus on the black numbers; thus, elementary features had not yet been grouped or bound to an object. Having participants attend to the target objects eliminated the illusory conjunction.