Reference frame and effects of orientation on finding the tops of rotated objects.

Effects of stimulus orientation across trial blocks and the spatial reference frame were investigated with a task in which Ss, with their head upright or tilted, judged a dot to be near the top or the bottom of rotated line drawings of objects. Objects used in this task were also named. Response times from the first block of trials increased linearly for objects rotated from 0 degrees to 120 degrees from the upright. Across blocks, orientation effects diminished for naming but remained the same for top-bottom discriminations. Practice with top-bottom discriminations diminished orientation effects when the same objects were subsequently named. The spatial reference frame for top-bottom discriminations was midway between retinal and environmental coordinates. Specifying the location of object features is of greater importance for top-bottom discriminations than for naming and underlies orientation effects in these tasks.