Neglect 13 the anterior cingulate were also active (BA 24).but tied to distinct sensory and motor systems.To not consistently address this question,Wojciulik and Kanwisher Nohre and colleagues (obre Sebestver (1999)used fMRI in three different tasks of visual Gitelman,Mesulam,1997).also using PET. attention.These tasks involved shifting attention found that an exogenous shift in attention wa matching obiects in different locations.and con associated with activation around the intraparieta joining visual features of an object at a specific loca sulcus.Taking advantage of fMRI's bette spatial tion.They found that the intraparietal sulcus wa resolution Corbetta and colleagues (Corb ett activated in all three tasks.While one cannot pr 1998)confirmed activation of the intr the null hypothesis that the intraparietal sul sulcus as well as the postce and pre involved in all attenti suleus with shifts of attention This act this area might mediate a eneral atte found even when explicit motor r selection module.Similarly.Coull and Frith (1998) ired that n be ged without motor in a PET study found that while the on The tial than prep. etal lobule s in the r 么 ietal sulcus nd precentral e whe direc nost striking aspect of neglect synd rather thar just shifting to a of contra solater in which ortex is also acti that spac into a d The stream (Ungerleider 982 Th am proc the spa the loca of objec s of inter n of eye mover ent might be dorsolatera y to ic corte and co-worke 1999)showed tha ormation to be aware of both the "where"and areas on attentional tasks is what”of objects probably not due to these processes However Attention modulates the activity of neural struc the studies did not completely control for tures in the ventral stream dedicated to identify- movements.which could be contributing to these ing objects.Patients with prefrontal damage are activations.Nonetheless. given that dorsolatera impaired in discriminating contralesional visual prefrontal cortex lesions also produce disorders of targets.This impairment is associated with dimin- attention.it is likely that these areas are linked to ished event-related potentials at 125 ms and lasting the posterior parietal regions involved in directing for another 500ms (Barcelo,Suwazono,Knight, spatial attention. 2000).These event-related potentials are linked to extrastriate processing.which is associated with Supramodal,Space-Based,and Object-Based tonic activation as well as the selection of features Attention and the postselection analyses of objects. The earliest point in visual processing at which A long-standing question about the organization attentional modulation can occur is not clear of attention is whether there is a supramodal all- Several studies suggest that the primary visual oaa“ohm cortex might be modulated attention (Brefczynski DeYoe,1999:Gandhi,Heeger.the anterior cingulate were also active (BA 24), but not consistently. Nobre and colleagues (Nobre, Sebestyen, Gitelman, & Mesulam, 1997), also using PET, found that an exogenous shift in attention was associated with activation around the intraparietal sulcus. Taking advantage of fMRI’s better spatial resolution, Corbetta and colleagues (Corbetta, 1998) confirmed activation of the intraparietal sulcus as well as the postcentral and precentral sulcus with shifts of attention. This activation was found even when explicit motor responses were not required, suggesting that these areas can be atten￾tionally engaged without motor preparation. They also found similar blood flow increases in the right intraparietal sulcus and precentral cortex when attention was directed at a peripheral location in a sustained manner, rather than just shifting to a peripheral location. The dorsolateral prefrontal cortex is also acti￾vated in most studies in which visual attention is shifted to different locations. These activations seem to center around the frontal eye fields (BA 6/8) and the adjacent areas. Working memory or in￾hibition of eye movement might be associated with dorsolateral prefrontal cortex activity. Gitelman and co-workers (Gitelman et al., 1999) showed that activation of these areas on attentional tasks is probably not due to these processes. However, the studies did not completely control for eye movements, which could be contributing to these activations. Nonetheless, given that dorsolateral prefrontal cortex lesions also produce disorders of attention, it is likely that these areas are linked to the posterior parietal regions involved in directing spatial attention. Supramodal, Space-Based, and Object-Based Attention A long-standing question about the organization of attention is whether there is a supramodal all￾purpose attention module, or whether attention is better viewed as a collection of different modules tied to distinct sensory and motor systems. To address this question, Wojciulik and Kanwisher (1999) used fMRI in three different tasks of visual attention. These tasks involved shifting attention, matching objects in different locations, and con￾joining visual features of an object at a specific loca￾tion. They found that the intraparietal sulcus was activated in all three tasks. While one cannot prove the null hypothesis that the intraparietal sulcus is involved in all attentional tasks, they suggest that this area might mediate a general attention and selection module. Similarly, Coull and Frith (1998) in a PET study found that while the superior pari￾etal lobule was more responsive to spatial than nonspatial attention, the intraparietal sulcus was responsive to both. The most striking aspect of neglect syndromes is that patients are unaware of contralesional space and of objects that inhabit that space. A central tenet of visual neuroscience is the relative segregation of visual information into a dorsal “where” stream and a ventral “what” stream (Ungerleider & Mishkin, 1982). The dorsal stream processes the spatial locations of objects of interest, whereas the ventral stream processes features necessary to identify the object. Somehow humans integrate these streams of information to be aware of both the “where” and “what” of objects. Attention modulates the activity of neural struc￾tures in the ventral stream dedicated to identify￾ing objects. Patients with prefrontal damage are impaired in discriminating contralesional visual targets. This impairment is associated with dimin￾ished event-related potentials at 125ms and lasting for another 500ms (Barcelo, Suwazono, & Knight, 2000). These event-related potentials are linked to extrastriate processing, which is associated with tonic activation as well as the selection of features and the postselection analyses of objects. The earliest point in visual processing at which attentional modulation can occur is not clear. Several studies suggest that the primary visual cortex might be modulated by attention (Brefczynski & DeYoe, 1999; Gandhi, Heeger, & Neglect 13