Awareness-independent gradual spread of object-based attention

Although attention can be directed at certain objects, how object-based attention spreads within an object and whether this spread interacts with awareness remain unclear. Using a modified spatial cuing paradigm with backward masking, we addressed these issues with either visible or invisible displays presenting the real (Experiment 1) and illusory (Experiment 2) U-shaped objects (UOs), whose ends and middles, the possible locations of the cue and target, have iso-eccentric distances from the fixation. These equidistant ends and middles of UOs offered us a unique opportunity to examine whether attention gradually spreads within a given object, i.e., within an UO, attention spreads from its cued-end to uncued-end via the uncued-middle. Despite the visibility (visible or invisible) of UOs, both experiments supported this gradual spread manner by showing a faster response of human participants (male and female) to the target in the uncued-middle than that in the uncued-end. Our results thus indicate a gradual spread of object-based attention and further reveal that this gradual spread is independent of both the "visual objectness" (whether the object is defined as the real or illusory boundaries) and conscious access to objects.