Motion correspondence in the Ternus display shows feature bias in spatiotopic coordinates.

How is the visual system able to maintain object identity as the objects or the eyes move? While many early studies have shown small or no influence of feature information on this correspondence process, more recent studies have shown large feature effects. Here we investigated if this incongruity might be due to the distance over which the feature influence has an effect. We used a variation of the Ternus display (Ternus, 1926), an ambiguous apparent motion display, in which two sets of three discs are presented and one can perceive either three discs moving together (group motion) or one disc jumping across the other two discs (element motion). We biased the percept toward element motion by matching the features of some of the discs. In Experiment 1, with the three discs aligned and moving vertically, we added a horizontal offset between the two sets of discs and found a strong bias toward element motion that decreased with increasing spatial offset. In Experiment 3 participants had to make horizontal saccades across the same Ternus displays so that the two Ternus frames were horizontally offset on the retina, but not in spatiotopic coordinates. We found that the bias showed a similar spatial range, but now it was clear that the range was set in spatial coordinates independently of the retinal position. These results show that feature information contributes to correspondence over a limited spatial range (Experiment 1) and that the range is imposed in spatial, not retinal, coordinates (Experiment 2).