Competition between color and luminance in motion correspondence.

The visual system needs to solve the correspondence problem (i.e., which elements belong together across space and time) to allow stable representations of objects. It has been shown that spatiotemporal and feature information can influence this correspondence process, but it is unclear how these factors interact with each other, especially when they are more or less prominent due to changes in contrast magnitude. We investigated this question using a variation of the Ternus display, an ambiguous apparent motion display, in which three elements can either be perceived as moving together (group motion) or as one element jumping across the others (element motion). In the first experiment, we biased the percept by presenting some of the elements with the same feature (isoluminant color or luminance), such that they were either compatible with group motion or with element motion (simple feature biases). To change the strength of the feature bias, we manipulated the contrast magnitude of the feature. In three more experiments we introduced competitive displays, in which some of the elements showed a color/luminance based element bias of varying contrast magnitude, while other elements showed a luminance/color based group bias of varying contrast magnitude (competing feature bias). We found that for a simple feature bias the contrast magnitude did not affect the strength of the bias. For competing feature biases, however, the contrast magnitude did influence correspondence, as the bias strength increased with contrast. The implications of our results for current motion and feature-based theories of correspondence are discussed.