Experiment 2: Stimuli and results.

Stimuli: The vertical surface is stereoscopically in front of the horizontal surfaces (A) or behind them (B). The green arrow indicates whether the vertical surface is stereoscopically “placed” forward or backward. The same is indicated for the horizontal surfaces by the red arrows. Results: The proportion of trials motion was perceived in a direction indicating that the decremented horizontal surface was grouped with the other horizontal surface (C), and trials for which motion was not perceived (D). There were too few ‘bidirectional’ responses, and too few responses in directions indicative of horizontal-vertical grouping to include in the graph. Vertical lines in C and D indicate +/- one standard error. Standard errors smaller than the markers are omitted.