Neglect Levander.1991).However.patients with lesions Mennemeier.Wertman.Heilman,1992:Rapcsak. restricted to the posterior parietal cortex can have Fleet,Verfaellie,Heilman,1988).Bilateral intentional neglect (Mattingley.Husain,Rorden. lesions to temporal-parietal areas may produce Kennard.Driver 1998:Triggs Gold Gerstle neglect for lower and near peripersonal space Adair,Heilman,1994).Mattingley and col- whereas bilateral lesions to the ventral temporal leagues (Mattingley,Bradshaw,&Phillips,1992) r and reported that slowness in the initiation of left far extrapersonal space.Neglect in the vert ward movements is associated with right posterio complex interpl lays between the lesions whereas slowness in the exec ward movements is associated with right anterio (Mennemeier.Chatteriee Heilman.1994) and suboo cal lesions Most nat ients with neglec Left neglect may also vary,depending on whether probably have mixtures of attentional and inten the stimuli are located in close perip onal space onal glect (Adair na Schwa )which may be Heilm or in far rganization ofs ting thar quite comp sp in ace is dis tinct from the nizati n furthe of these (Pr gathe d th e body's nction the e link of gested ini trunk lly by B 941).w and the ect the P construc e reach of one's 1995:Ch terjee,1998).The rele Spatial Reference Frames tinction may a 6 by an tion c Objects in extrapersonal space are anchored to dif other by directi of limb movem ence I ames. interpretation would be conso nant with single-cel Viewe neurophysiological data from we can show that attentional neurons in the postenor pan locate a chair in a room in each of these frames etal cortex are selectively linked to eye or to limb A viewer-centered frame would locate the chair to movements (Colby.1998) the left or right of the viewer.This frame itself is divided into retinal,head-centered.or body- Spatial Attention in Three Dimensions centered frames.An object-centered frame refers to the intrinsic spatial coordinates of the object itselt, Neglect is usually described along the horizontal its top or bottom or right and left.These coordinates (left-right)axis.However,our spatial environment are not altered by changes in the position of the also includes radial (near-far)and vertical (up viewer.The top of the chair remains its top regard- down)axes.Neglect may also be evident in these less of where the viewer is located. coordinate systems.Patients with left neglect An environment-centered reference frame refers frequently have a more subtle neglect for near to the location of the object in relation to its envi- space.On cancellation tasks they are most likely ronment.The chair would he coded with respect to to omit targets in the left lower quadrant in which other obiects in the room and how it is related left and near neglect combine (Chatterjee et al to gravitational coordinates.The vestibular system 1999:Mark Heilman,1997).Patients with bilat through the otolith organs probably plays an impor eral lesions may have dramatic vertical and radial tant role in establishing the orientation of an object neglect (Butter.Evans.Kirsch.Kewman.1989: in relationship to the environmental vertical axisLevander, 1991). However, patients with lesions restricted to the posterior parietal cortex can have intentional neglect (Mattingley, Husain, Rorden, Kennard, & Driver, 1998; Triggs, Gold, Gerstle, Adair, & Heilman, 1994). Mattingley and col￾leagues (Mattingley, Bradshaw, & Phillips, 1992) reported that slowness in the initiation of left￾ward movements is associated with right posterior lesions, whereas slowness in the execution of left￾ward movements is associated with right anterior and subcortical lesions. Most patients with neglect probably have mixtures of attentional and inten￾tional neglect (Adair, Na, Schwartz, & Heilman, 1998b), which may be related in quite complex ways. One problem in the interpretation of these studies is that attention versus intention may not be the relevant distinction. Rather, the “attention” experi￾mental conditions may reflect the link of attention to eye movement and the “intention” conditions may reflect the link of attention to limb movements (Bisiach et al., 1995; Chatterjee, 1998). The relevant distinction may actually be between two perceptual￾motor systems, one led by direction of gaze and the other by direction of limb movements. Such an interpretation would be consonant with single-cell neurophysiological data from monkeys, which show that attentional neurons in the posterior pari￾etal cortex are selectively linked to eye or to limb movements (Colby, 1998). Spatial Attention in Three Dimensions Neglect is usually described along the horizontal (left-right) axis. However, our spatial environment also includes radial (near-far) and vertical (up￾down) axes. Neglect may also be evident in these coordinate systems. Patients with left neglect frequently have a more subtle neglect for near space. On cancellation tasks they are most likely to omit targets in the left lower quadrant in which left and near neglect combine (Chatterjee et al., 1999; Mark & Heilman, 1997). Patients with bilat￾eral lesions may have dramatic vertical and radial neglect (Butter, Evans, Kirsch, & Kewman, 1989; Mennemeier, Wertman, & Heilman, 1992; Rapcsak, Fleet, Verfaellie, & Heilman, 1988). Bilateral lesions to temporal-parietal areas may produce neglect for lower and near peripersonal space, whereas bilateral lesions to the ventral temporal structures are associated with neglect for upper and far extrapersonal space. Neglect in the vertical axis probably represents complex interplays between the visual and vestibular influences on spatial attention (Mennemeier, Chatterjee, & Heilman, 1994). Left neglect may also vary, depending on whether the stimuli are located in close peripersonal space or in far extrapersonal space, suggesting that the organization of space in peripersonal space is dis￾tinct from the organization in further extrapersonal space (Previc, 1998). This notion of concentric shells of space around the body’s trunk was sug￾gested initially by Brain (1941), who proposed that peripersonal space is a distinct spatial construct defined by the reach of one’s limbs. Spatial Reference Frames Objects in extrapersonal space are anchored to dif￾ferent reference frames. These frames are generally divided into viewer-, object-, and environment￾centered reference frames. For example, we can locate a chair in a room in each of these frames. A viewer-centered frame would locate the chair to the left or right of the viewer. This frame itself is divided into retinal, head-centered, or body￾centered frames. An object-centered frame refers to the intrinsic spatial coordinates of the object itself, its top or bottom or right and left. These coordinates are not altered by changes in the position of the viewer. The top of the chair remains its top regard￾less of where the viewer is located. An environment-centered reference frame refers to the location of the object in relation to its envi￾ronment. The chair would be coded with respect to other objects in the room and how it is related to gravitational coordinates. The vestibular system through the otolith organs probably plays an impor￾tant role in establishing the orientation of an object in relationship to the environmental vertical axis Neglect 9