Journal of the International Neuropsychological Society (2013), 19, 1–9. Copyright E INS. Published by Cambridge University Press, 2012. doi:10.1017/S1355617712000963 Egocentric and Allocentric Spatial Representations in Williams Syndrome Ine ˆs Bernardino, 1 Susana Mouga, 1,2 Miguel Castelo-Branco, 1 AND Marieke van Asselen 1 1 Visual Neuroscience Laboratory, IBILI, Faculty of Medicine, Coimbra, Portugal 2 Child Center, Neurodevelopment and Autism Department, Pediatric Hospital of Coimbra, CHUC, Coimbra, Portugal (RECEIVED January 10, 2012; FINAL REVISION June 13, 2012; ACCEPTED June 14, 2012) Abstract Williams syndrome (WS) is a neurodevelopmental disorder characterized by severe visuospatial deficits, particularly affecting spatial navigation and wayfinding. Creating egocentric (viewer-dependent) and allocentric (viewer-independent) representations of space is essential for the development of these abilities. However, it remains unclear whether egocentric and allocentric representations are impaired in WS. In this study, we investigate egocentric and allocentric frames of reference in this disorder. A WS group (n 5 18), as well as a chronological age-matched control group (n 5 20), a non- verbal mental age-matched control group (n 5 20) and a control group with intellectual disability (n 5 17), was tested with a computerized and a 3D spatial judgment task. The results showed that WS participants are impaired when performing both egocentric and allocentric spatial judgments even when compared with mental age-matched control participants. This indicates that a substantial deficit affecting both spatial representations is present in WS. The egocentric impairment is in line with the dorsal visual pathway deficit previously reported in WS. Interestingly, the difficulties found in performing allocentric spatial judgments give important cues to better understand the ventral visual functioning in WS. (JINS, 2013, 19, 1–9) Keywords: Spatial cognition, Reference frames, Dorsal visual stream, Viewer-dependent coordinates, Viewer-independent coordinates, Visuospatial INTRODUCTION Williams syndrome (WS) is a genetic neurodevelopmental disorder resulting from a hemideletion on chromosome 7q11.23 (Bayes, Magano, Rivera, Flores, & Perez-Jurado, 2003; Korenberg et al., 2000). This rare syndrome is character- ized by a specific cognitive profile defined by a predominant visuospatial impairment while language processing is relatively spared (Bellugi, Lichtenberger, Jones, Lai, & St George, 2000). Visuospatial deficits have been widely reported in WS, par- ticularly concerning the perception of two-dimensional (2D) form-from-motion stimuli (Reiss, Hoffman, & Landau, 2005), the discrimination of coherent motion and action planning (Atkinson et al., 2003). Furthermore, a decreased efficiency in visual search was reported and is characterized by a less structured scan-pattern. This involves an increase in fixation duration and number of fixations which results in more time required to process the visual scene (Montfoort, Frens, Hooge, Haselen, & van der Geest, 2007). WS participants were also found to be impaired on visual working memory tasks requiring the recognition of the location of a previously presented object appearing in one of four quadrants (Vicari, Bellucci, & Carlesimo, 2005). These deficits regarding the processing of spatial information have been demonstrated in small-scale as well as in large-sale environ- ments (Farran, Courbois, & Cruickshank, 2009). WS participants were found to be slightly impaired in learning a route in the real world (Farran, Blades, Boucher, & Tranter, 2010) and in correctly performing wayfinding tasks (Atkinson et al., 2001). The aforementioned weaknesses have important outcomes for the daily life of these patients which are evidenced by their parents’ reports revealing difficulties in following directions and establishing their perceptual organization of space (Semel & Rosner, 2003). The develop- ment of the spatial representation of the surrounded space under different frames of reference is pivotal for the acquisition of spatial navigation and wayfinding abilities. Nardini, Atkinson, Braddick, and Burgess (2008), defined developmental trajectories of different spatial frames of reference in WS by using a spatial memory paradigm Correspondence and reprint requests to: Ine ˆs Bernardino, IBILI - Visual Neuroscience Laboratory, Faculty of Medicine, University of Coimbra, Azinhaga de Santa Comba, 3000-354 Coimbra, Portugal. E-mail: ibernardi- no@fmed.uc.pt 1