Abstract
We recently reported (Psychonomic Society Meeting, 2003) that when objects were in optical contact with both a ground and ceiling surface, layout was determined by ground contact (a ground dominance effect). Here we report two new experiments testing whether the ground dominance effect depends on where the judgment is made. The stimuli in the first experiment were composed of checkerboard textured ground and ceiling planes tilted either to the right or to the left, with two striped vertical posts at the same distance from the observer and at the same height in the image. One post was attached to the ground and had a gap between its top surface and the ceiling; the other was attached to the ceiling and had a gap between its bottom surface and the ground. Optical contact with the ground thus indicated that one post was closer to the observer, whereas optical contact with the ceiling indicated that the other post was closer. A blue dot was attached to each post at the same height. The height of the dots varied randomly over trials from the bottom to the top of the posts. On each trial the observer moved a mouse cursor over the dot that appeared to be closer and clicked on it. The proportion of judgments consistent with ground contact was 1.0 when the dots were at the bottom of the posts and dropped as the dots were placed higher, but remained close to .75 with the dots at the top of the posts. This showed that a ground dominance effect was present even when the judgment was made at a location close to the ceiling. We also found an increase in response time as the dots were moved from the bottom to the top of the posts. In the second experiment the posts were replaced by gray ellipses in order to eliminate any effect of the regular striped texture and the shape of the posts. The task was the same as in the first experiment and similar results were found. Overall, we found that the ground dominance effect cannot be explained by the location of the judgment.
Supported by NIH Grant EY-12437.