Egocentric and object-based transformations in the laterality judgement of human and animal faces and of non-corporeal objects.

Mental rotation of body parts is influenced by specific sensory-motor information, and may be performed using an egocentric (subject-based) or an object-based mental transformation. Neurologically healthy volunteers were asked to verbally judge the laterality of visually presented human face, owl face and front of a car with a black patch over one eye/headlight, presented in one of eight orientations. Subjects may or may not have their head held in a head brace. The transformation used to solve the task was assessed with a questionnaire. Response times were non-monotonical at 180 degrees for the object-based group, but not for the group using egocentric transformation. Having head movement constrained by the use of a head brace ("fixed") or not ("moving") did not influence performance. Within the two groups, no differences were found between the three types of stimuli. Hence, the response profile for mental rotation of human faces and face-like stimuli depended on the type of mental spatial transformation used to solve the task, independently from the possibility to move the head and from the kind of stimuli processed.