Human Brain Activity Related to the Perception of Spatial Features of Objects Isabelle Faillenot,* , † Jean Decety,* , † ,1 and Marc Jeannerod‡ *INSERM U280, 151 cours Albert Thomas, 69003 Lyon, France; †CERMEP, 59 boulevard Pinel, 69003 Lyon, France; and ‡Institut des Sciences Cognitives, 67 boulevard Pinel, 69675 Bron, France Received September 23, 1998 The role of the parietal cortex in visuospatial analy- sis of object was investigated by cerebral blood flow measurements in seven subjects using positron emis- sion tomography. Data were acquired while subjects performed a matching task requiring the discrimina- tion of simultaneously presented objects based on one of their spatial properties. Three properties were stud- ied separately during three scanning conditions re- peated twice: surface orientation, principal axis orien- tation, and size. Scans were also obtained during a sensorimotor control task (similar visual stimulation, same motor action, voluntary saccades toward each object) as well as during rest (no stimulation, eyes closed). Compared to rest, the three property match- ing tasks showed the same pattern of activation: the whole occipital lobe, the right intraparietal sulcus (IPS), and the right occipitotemporal (OT) junction. Compared to the control condition, only right IPS and OT junction were significantly activated during dis- crimination of the spatial properties. The IPS focus was located between the superior parietal lobule and the angular gyrus, and the OT activation overlapped the posterior part of the inferior temporal gyrus and the middle occipital gyrus. These results indicate that discrimination of spatial attributes requires the activa- tion of both the parietal and the temporal cortices of the right hemisphere and provide further evidence that the IPS plays a critical role in visuospatial analy- sis of objects.  1999 Academic Press Key Words: PET; functional anatomy; vision; percep- tion; object orientation; object size; temporal cortex; parietal cortex INTRODUCTION A well-known model has postulated that the visual cortex is organized into two distinct pathways both originating in the primary visual cortex. The ventral pathway, which reaches the inferotemporal cortex, is involved in object perception whereas the dorsal path- way, which projects into the parietal cortex, is engaged in visuospatial perception (e.g., Ungerleider and Mish- kin, 1982). Later, Milner and Goodale substantially reinterpreted these functions on the basis of neuropsy- chological dissociations. They postulated that both pathways process the same visual information about objects but with different purposes. The dorsal stream would process visual information for controlling actions on objects, whereas the ventral stream would extract cues for object perception and identification (Goodale and Milner, 1992; Milner and Goodale, 1995). Although these two models may provide useful generalizations, they do not fully reflect the complexity of the cortical operations and the close cooperation that exists be- tween both systems (see, for example, Merigan and Maunsell, 1993). In a previous PET study in human subjects, Faillenot et al. (1997b) found that grasping objects involved only parietal regions while shape matching was associated with temporal and parietal activations. The fact that a common parietal region (anterior intraparietal sulcus, IPS) was involved in both tasks underlines that percep- tion and action are not completely independent pro- cesses and further demonstrates that the parietal cortex participates in object perception. One possible interpretation of Faillenot et al.’s data is that this IPS region plays a role in integrating some spatial proper- ties of objects such as orientation, size, and the relative location of object parts. Those properties are equally important for grasping and for identifying object shape. This interpretation is congruent with the finding that monkey IPS neurons may exhibit selectivity for 3D structure of objects; e.g., they may fire when an object of the preferred configuration is seen or grasped (for a recent review, see Sakata et al., 1997). In the anterior part of IPS (area AIP), neurons may encode spatial characteristics of objects for manipulation (Taira et al., 1990). In the caudal part of the lateral bank of IPS, 1 To whom correspondence should be addressed. E-mail: decety@lyon151.inserm.fr. NeuroImage 10, 114–124 (1999) Article ID nimg.1999.0449, available online at http://www.idealibrary.com on 114 1053-8119/99 $30.00 Copyright  1999 by Academic Press All rights of reproduction in any form reserved.