Neuropsychologia 45 (2007) 2553–2560 Object-centred neglect: Simulation with head-centred coding based on Gaussian gaze-dependent units Massimo Silvetti a,b,∗ , Eliano Pessa c , Fabrizio Doricchi a,b a Fondazione Santa Lucia IRCCS, Roma, Italy b Dipartimento di Psicologia, Universit` a degli Studi di Roma “La Sapienza”, Italy c Dipartimento di Psicologia, Universit` a degli Studi di Pavia, Italy Received 14 September 2006; received in revised form 7 March 2007; accepted 13 March 2007 Available online 23 March 2007 Abstract Right brain damaged patients affected by contralesional object-centred neglect are able to process all objects around them but systematically omit the left part of these objects. We show that pure object-centred neglect can be simulated by a basis function neural network in which the activity of units allowing head-centred coding of space is based on the activity of gaze-dependent units with no lateral gradient of preferred eye positions along the horizontal space. This type of network simulates complete dissociation between object-centred and egocentric neglect, as observed in patients’ copies of multi-item drawings. Based on these results and available neurophysiological, clinical and brain imaging data, it is proposed that disruption of a cerebral network including dorsal occipital and parietal areas and the supplementary eye fields could be the main cause of object-centred neglect. © 2007 Elsevier Ltd. All rights reserved. Keywords: Neural model; Visual; Object-centred neglect; Neglect; Coordinate transformation; Space; Attention 1. Introduction The neglect syndrome is a frequent consequence of right parietal-frontal cortical-sub-cortical brain damage (Doricchi & Tomaiuolo, 2003; Gaffan & Hornak, 1997; Leibovitch et al., 1998; Mort et al., 2003; Thiebaut de Schotten et al., 2005) caus- ing unawareness of the left side of personal and extra-personal space, objects and mental images (Bartolomeo & Chokron, 2002). This invalidating syndrome frequently affects different spatial reference frames simultaneously (Bisiach, Capitani, & Porta, 1985; Calvanio, Petrone, & Levine, 1987; Farah, Brunn, Wong, Wallace, & Carpenter, 1990; Ladavas, 1987). When tested in copy drawing, neglect patients typically omit objects placed to the left of the head-body midline, providing com- plete copy of objects placed to the right of the body midline (i.e., egocentric or body-centred neglect; Walker, 1995). More rarely, and curiously, some patients are able to detect all of the ∗ Corresponding author at: Dipartimento di Psicologia 39, Universit` a degli Studi di Roma “La Sapienza”, Via dei Marsi 78, 00185 Roma, Italia. Tel.: +39 06 49917929/51501509. E-mail address: massimo.silvetti@uniroma1.it (M. Silvetti). objects in a multi-item model but systematically omit copying the left side of the very same objects. This form of neglect, first described by Apfeldorf (1962) and originally defined by Gainotti and Tiacci (1970) “piece-meal” neglect, is now commonly called “object-based” neglect and has been described in several clini- cal reports (for a review see Olson, 2003). Object-based neglect can, in turn, affect two different frames of reference (Olson, 2003): (a) an “object-aligned” frame such that the left side of objects with canonical horizontal orientation (i.e., letters and words) or with gravitationally defined left and right sides is neglected regardless of canonical (i.e., “R”) or mirror-reversed presentation (i.e., “Я”), and regardless of object rotations on the frontal plane (Behrmann & Moscovich, 1994; Driver, Baylis, Goodrich, & Rafal, 1994; Driver & Halligan, 1991; Tipper & Behrmann, 1996); (b) an “object-centred” frame, such that the left side of objects without canonical left–right orientation is neglected independently of their lateral egocentric spatial posi- tion as typically observed in patients’ copies of multi-item line drawings (Fig. 1)(Doricchi & Galati, 2000; Gainotti & Tiacci, 1970; Marshall & Halligan, 1993; Pachalska, Franczuk, MacQueen, & Talar, 2004; Walker, Findlay, Young, & Lincoln, 1996). 0028-3932/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2007.03.012