Abstract

The feature integration theory (Treisman et ai., 1982) predicts that illusory conjunctions are not affected by the distance between stimuli. The location uncertainty hypothesis (Ashby et al., 1996), however, proposes that illusory conjunctions occur only between the adjacent stimuli. Four experiments investigated the distance effect of illusory conjunction. Using a new primary task in which memory load is minimized Experiment 1 showed that illusory conjunctions occurred only between the adjacent items when only two letters was displayed and perceptual grouping was controlled. In Experiment 2, a nontarget was added in the display, and increased attentional load and perceptual grouping was manipulated (horizontal, vertical, and random array). Attentional load made quite large illusory conjunctions between letters at far distances, but perceptual grouping had no effect at far distances. In Experiment 3, small attention load conditions demonstrated a clear distance effect, whereas a large load produced about same amount of illusory conjunctions at all distances. Finally, Experiment 4 replicated the results on the random array condition in ex. 2 and ex. 3, and confirmed that illusory conjunctions are an attentional failure in nature rather than a sensory failure. Also it implicated that illusory conjunctions between the adjacent letters and those between the far letters may be influenced by the different variables.