Motion grouping: Spatial manipulations of contrast in the ternus display

In the Ternus display, group motion is generally seen at long ISI durations, and element motion at short ISI durations. If the Ternus display is thought of in terms of a space-time plot, grouping of elements within and between frames can be seen as a means of solving the problem of what motion percept will be seen at what time. Grouping and perceived surface properties in static displays can be influenced by luminance configuration (e.g. Spehar and Zaidi, 1996). An adapted form of He and Ooi's (1999) stimulus containing occluders between the tokens was used to examine whether manipulations that affect grouping in a static display would affect motion grouping in a first-order and a second-order display. For a first-order display, there was a significant increase in group motion responses in conditions in which tokens and occluders were of the same contrast polarity, compared to conditions in which the tokens and occluders were of opposite contrast polarity. Results for the second-order display were equivocal. These findings indicate that factors that affect grouping and perceived surface properties in static displays can also affect the perception of motion grouping in the Ternus display, suggesting that similar principles are involved in both cases.