Abstract
We used Ternus motion to test whether the selection of visual information can be mediated by the perceived object structure of dynamic displays separate from stimulus locations. Ternus displays consist of two cycling stimulus frames, separated by a blank interstimulus interval (ISI) of varying length. Each frame contains (for example) a row of three discs that are translated by one position between frames. At short ISIs, observers tend to perceive “element motion” where a single disc appears to “jump” from one end of the row to the other. At long ISIs, observers tend to perceive “group motion” where all three discs appear to translate back and forth together. These two percepts represent mutually exclusive perceptual organizations of which objects went where (i.e., object correspondence). We added a small gap in the upper-left, lower-left, upper-right, or lower-right of one disc of each of the final two frames of motion. Observers reported whether the final gap appeared on the left or right side of the disc. We measured response time (RT) as a function of ISI (short versus long) and the relative image-locations of the two discs in which gaps appeared (i.e., in the same image-location or adjacent image-locations). When the two gaps were presented in the same image-location, they were perceived as parts of the same object during element-motion (short ISIs), but as parts of different objects during group-motion (long ISIs). The reverse was true when the two gaps were presented in adjacent image-locations. Object status and image location are thereby dissociable through interactions between ISI and image location. In multiple variations of this experiment, reliable interactions between ISI and image location occurred. We conclude that the selection of visual information in dynamic displays is systematically mediated by the object organization of the scene, not simply stimulus location.