Top-bottom and front-behind decisions on rotated objects.

Human adults decided whether a dot was nearer the top or bottom of rotated drawings of objects in a top-bottom task, and whether a dot was at the front of or behind rotated objects in a front-behind task. These two tasks were performed with the head upright and with the head tilted clockwise and counterclockwise in separate blocks of trials in order to dissociate retinal from environmental perceptual frames of reference. Response times increased approximately linearly with increasing departure from the orientation of the perceptual reference frame in both tasks and the magnitude of the effect was similar across tasks. In the head tilted conditions, the perceptual frame of reference was located midway between the environmental and retinal upright for both tasks.