Mental rotation for spatial environment recognition.

We investigated the importance of retinal and body inclination in the recognition of spatial environment. The paradigm involved the recognition, in body upright and tilted conditions, of tilted images -intervals of 15 degrees from 0 degrees to 90 degrees leftward and rightward respective to head coordinates - of known spatial layouts encountered while walking in Paris. The analysis of reaction times was consistent with the subjects mentally rotating the spatial layout so that the environment was subjectively vertical before making their decisions. In contrast, when the body was roll-tilted (33 degrees ), overall reaction time was not affected; however, reaction time and spatial layout tilt with respect to the head were correlated when the body was tilted but not when upright. Both results indicate that gravity was slightly important in performing the task.