Neglect 5 Attentional Theories weak vector.Therefore,after right brain damage the left hemisphere's unfettered vector of attention Attentional theories are based on the idea that is powerfully oriented to the right.Since the right neglect is a disorder of spatial attention.Spatial hemisphere's intrinsic vector of attention is only attention is the process by which objects in certain weakly directed after left brain damage,there is not a similar orientation bias to the left.Thus,right sided neglect is less common than left-sided volve selection for perception or for actions.The idea that objects in spatial locations are selected for Heilman and co-workers,in contrast to action has ven rise to the notion of"intentional neglect,"in which patients are disinclined to act in tial attention (Heilman or toward contralesional space.(Intentional eg 1979:Heilman Van Den Abell.1980).Patients is discussed more fully later in this cha Attention is gen rally phic slowing than with left br ope Normally. the They also demonst rate nished sses ed with Visual subjects left her visual scene eiagaceod e righ to be cap The oth often oper spa while the acros ent spatial locati afte h nage can produc left.Thus. isphere is i fter Vecera the right and no often have relatively preserved preattentive vision. occur with the same severity as after right brair as evidenced by their ability to separate figure from damage.Mesulam (1981.1990).emphasizing the ground and their susceptibility to visual illusions distributed nature of neural networks dedicated (Driver,Baylis,Rafal,1992:Mattingley,Davis. to spatial attention.also proposed a similar hemi Driver,199/:Ricci,Calhoun, spheric organization for spatial attention 2000:Vallar.Daini.Antonucci.2000) Posner and colleagues proposed an influential In neglect.attention is directed ipsilesionally model of spatial attention composed of elementary and therefore patients are aware of stimuli only in operations.such as engaging.disengaging.and this sector of space.A major concern of general shifting (Posner,Walker,Friedrich,Rafal,1984: attentional theories is to understand why neglect Posner Dehaene.1994).They reported that is more common and severe after right than after patients with right superior parietal damage are left brain damage.Kinsbourne postulates that each selectively impaired in disengaging attention from hemisphere generates a vector of spatial attention right-sided stimuli before they shift and engage directed toward contralateral space,and these left-sided stimuli.This disengage deficit is likely to attentional vectors are inhibited by the opposite account for some symptoms of visual extinction. hemisphere (Kinsbourne,1970.1987).The left In more recent versions of this theory.Posner and hemisphere's vector of spatial attention is strongly colleagues proposed a posterior and an anterion biased,while the right hemisphere produces only a attentional network,which bears considerableAttentional Theories Attentional theories are based on the idea that neglect is a disorder of spatial attention. Spatial attention is the process by which objects in certain spatial locations are selected for processing over objects in other locations. The processing may in￾volve selection for perception or for actions. The idea that objects in spatial locations are selected for action has given rise to the notion of “intentional neglect,” in which patients are disinclined to act in or toward contralesional space. (Intentional neglect is discussed more fully later in this chapter.) Attention is generally considered effortful and usually operates serially. Normally, the nervous system processes visual information in stages. Visual elements, such as color, movement, and form, are extracted initially from the visual scene. These elements are segregated or grouped together “preattentively,” to parse the visual scene before attention is engaged. Preattentive processing is generally considered automatic and often operates in parallel across different spatial locations. Brain damage can produce selective deficits at this preat￾tentive level with relatively normal spatial attention (Ricci, Vaishnavi, & Chatterjee, 1999; Vecera & Behrmann, 1997). By contrast, patients with neglect often have relatively preserved preattentive vision, as evidenced by their ability to separate figure from ground and their susceptibility to visual illusions (Driver, Baylis, & Rafal, 1992; Mattingley, Davis, & Driver, 1997; Ricci, Calhoun, & Chatterjee, 2000; Vallar, Daini, & Antonucci, 2000). In neglect, attention is directed ipsilesionally, and therefore patients are aware of stimuli only in this sector of space. A major concern of general attentional theories is to understand why neglect is more common and severe after right than after left brain damage. Kinsbourne postulates that each hemisphere generates a vector of spatial attention directed toward contralateral space, and these attentional vectors are inhibited by the opposite hemisphere (Kinsbourne, 1970, 1987). The left hemisphere’s vector of spatial attention is strongly biased, while the right hemisphere produces only a weak vector. Therefore, after right brain damage, the left hemisphere’s unfettered vector of attention is powerfully oriented to the right. Since the right hemisphere’s intrinsic vector of attention is only weakly directed after left brain damage, there is not a similar orientation bias to the left. Thus, right￾sided neglect is less common than left-sided neglect. Heilman and co-workers, in contrast to Kinsbourne, propose that the right hemisphere is dominant for arousal and spatial attention (Heilman, 1979; Heilman & Van Den Abell, 1980). Patients with right brain damage have greater electroen￾cephalographic slowing than those with left brain damage. They also demonstrate diminished gal￾vanic skin responses compared with normal control subjects or patients with left hemisphere damage (Heilman, Schwartz, & Watson, 1978). This dimin￾ished arousal interacts with hemispheric biases in directing attention. The right hemisphere is thought to be capable of directing attention into both hemi￾spaces, while the left hemisphere directs attention only into contralateral space. Thus, after right brain damage, the left hemisphere is ill equipped to direct attention into left hemispace. However, after left brain damage, the right is capable of directing atten￾tion into both hemispaces and neglect does not occur with the same severity as after right brain damage. Mesulam (1981, 1990), emphasizing the distributed nature of neural networks dedicated to spatial attention, also proposed a similar hemi￾spheric organization for spatial attention. Posner and colleagues proposed an influential model of spatial attention composed of elementary operations, such as engaging, disengaging, and shifting (Posner, Walker, Friedrich, & Rafal, 1984; Posner & Dehaene, 1994). They reported that patients with right superior parietal damage are selectively impaired in disengaging attention from right-sided stimuli before they shift and engage left-sided stimuli. This disengage deficit is likely to account for some symptoms of visual extinction. In more recent versions of this theory, Posner and colleagues proposed a posterior and an anterior attentional network, which bears considerable Neglect 5