Localizing the object tracked by attention

Purpose. Attention plays a crucial role determining the direction of motion perceived in an ambiguous apparent motion display. For example, alternation of frames A and B (see figure) can be seen as either clockwise or counterclockwise motion of disks. In such cases, some kind of token or pointer or even attention (Shioiri, 1995; Wertheimer, 1912) may be moving along the path between the visible disks during the ISI when no disks are present. We used a perpendicular bisector probe to judge the apparent location of target object during the ISI. Method. A target disk was identified for tracking in a repeating alternation of frames A and B with 105 msec ISIs. Observers maintained tracking in the same direction for about 2 seconds at which point two probe dots were presented during the ISI. The observer responded whether the apparent position of the target (not actually present during the ISI) was ahead of or behind the perpendicular bisector of the line connecting the two probe dots (no lines were actually presented). Observers were remarkably accurate at this task and responses were measured for different probe positions and different times within the ISI. Results. The apparent location of the target disk changed monotonically over time during the ISI. Conclusions. These results suggest that some internal representation moves smoothly along the path of the apparent motion during the intervals when the physical stimulus is not presented. (Graph Presented).