Vol.:(0123456789) 1 3 Exp Brain Res (2018) 236:275–284 DOI 10.1007/s00221-017-5125-y RESEARCH ARTICLE Dissociating object-based from egocentric transformations in mental body rotation: efect of stimuli size Hamdi Habacha 1,2  · David Moreau 3  · Mohamed Jarraya 4  · Laure Lejeune-Poutrain 1  · Corinne Molinaro 1   Received: 20 May 2017 / Accepted: 7 November 2017 / Published online: 11 November 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 manipulations involved during object-based and egocentric transformations. Keywords Mental rotation · Object-based transformations · Egocentric transformations · Mental size transformations · Motor processes. Introduction Mental rotation and mental size transformation Interaction with objects from everyday life takes place through several mental processes. Among these processes, mental rotation (MR), the ability to generate and rotate inter- nal representations of objects, seems to play a crucial role in the identifcation of and the interaction with objects. Mental rotation concept was frst introduced as a seminal paradigm in cognitive psychology by Shepard and Metzler (1971). In their classic chronometric MR task, Shepard and Metzler asked participants to judge whether two rotated images of asymmetric objects depict identical or diferent objects. Reaction times (RT) on this task increased as a function of the angular disparity between the target and comparison stimulus matching the increasing physical rotation time of a real object. These results show the equivalence between mental and real rotation, and suggest that mental rotation process is an internal equivalent to the physical rotation of a real object (Shepard and Metzler 1971). Moreover, objects of everyday life are present in very diferent sizes. Considering the large diferences between their sizes, processes of mental size transformation seem to be as critical as mental rotation itself to efectively interact with objects. Mental size transformation is another form of mental imagery where subjects mentally transform the size Abstract The efect of stimuli size on the mental rota- tion of abstract objects has been extensively investigated, yet its efect on the mental rotation of bodily stimuli remains largely unexplored. Depending on the experimental design, mentally rotating bodily stimuli can elicit object-based trans- formations, relying mainly on visual processes, or egocentric transformations, which typically involve embodied motor processes. The present study included two mental body rotation tasks requiring either a same–diferent or a lateral- ity judgment, designed to elicit object-based or egocentric transformations, respectively. Our fndings revealed shorter response times for large-sized stimuli than for small-sized stimuli only for greater angular disparities, suggesting that the more unfamiliar the orientations of the bodily stimuli, the more stimuli size afected mental processing. Impor- tantly, when comparing size transformation times, results revealed diferent patterns of size transformation times as a function of angular disparity between object-based and egocentric transformations. This indicates that mental size transformation and mental rotation proceed differently depending on the mental rotation strategy used. These fndings are discussed with respect to the diferent spatial * Hamdi Habacha hamdi.habacha@gmail.com 1 Laboratoire Psychologie de la Perception (UMR CNRS 8242), 45 rue des Saints Pères, 75006 Paris, France 2 Université de Caen Basse-Normandie CesamS, EA 4260, UNICAEN, 14032 Caen, France 3 School of Psychology and Centre for Brain Research, University of Auckland, Auckland, New Zealand 4 Research Unit (EMCS), High Institute of Sport and Physical Education, Sfax University, Sfax, Tunisia