Perceptual grouping of objects occupied by target and flankers affects target-flanker interference

We report four experiments that tested whether object-based attentional spreading can be modulated by the perceptual structure of objects occupied by target and flankers in a flanker task. The target and flankers were presented on a single object or three separate objects (of same or different shape), displayed at fixed, known locations. The flanker compatibility effect was larger when the target and flankers were on the same object or on three objects of the same shape than when they were on three objects of different shapes, indicating that perceptual grouping of background objects occupied by target and flankers can affect the target-flanker interference. These results imply that attention likely spreads across different objects occupied by target and flankers when these objects are separated by small gaps or have identical shapes, and attentional spreading is impeded when these objects have different shapes, suggesting that object-based attentional spreading can be modulated by the perceptual structure of objects.