Abstract
How is attention distributed within a spatially extended object? Some evidence suggests that, with multiple seconds of viewing, attention comes to be peaked at the center of an object, even when the end of an object is cued in top-down manners (Alvarez & Scholl, 2005). In addition, eye movements to objects often land at the center of gravity of the object (e.g., Kowler & Blaser, 1995; Melcher & Kowler, 1995), consistent with the idea that covert attention (prior to the saccade) comes to be concentrated at the center of the object. In the latter case, however, center of gravity effects have been observed for goal-directed saccades at relatively long latencies and thus might not reflect the automatic spread of attention through an object. In the present study, we examined the extent to which rapidly generated saccades to a part of an object are biased toward the center of the object. While one end of an extended object was cued, observers attempted to execute a saccade to that region of the object. Part structure was manipulated, with either strong image-based cues to segment the object into parts or no such cues. We predicted that part structure would constrain the spread of attention within the object, reducing the tendency for saccades to be biased toward the center of the object. Surprisingly, in contrast with earlier studies, the landing position of the saccade was not significantly biased toward the object center in either condition. These results indicate that covert attention prior to a saccade can be maintained within one part of an object and does not automatically come to be concentrated in the center.