Anian chatteriee 10 (Mennemeier et al 1994:Pizzamiglio vallar tactile awareness (Vaishnavi et al.,1999).Since Doricchi.1997).Several reports de onstrate that 、with neglect may hay nal neglect ccur in an of these refer ence fra (Bisiach et al..1986)or deficit of their ov vitch Rlack Mozer 1994 schema (Coslett. 1998).the que of bo Chatteriee 1994:Driver Halli &C Tactil ced 1995:Laday arpent 1990,Hi being ced h patia suggesti ention operates across these different pect of the extrapersona Crss-Modal inte the space (Vaishnavi,Calhoun, Humans have a cohe erent sense of space in which pcpe2001 they perceive objects and act (Driver Spence Guiding mov nents by vision also involve 1998).Neglect studies visual signals nsual-moto r mapping can be altered if a subject of space.Presumably,multiple sensory modalities wears prisms that displace stimuli to the left or right interact in complex ways to give rise to multiple of their field of view.Recent work suggests tha representations of space. patients with neglect who are wearing prisms tha Rubens and colleagues (Rubens,1985)de- displace visual stimuli to their right remap ballisti monstrated that left-sided vestibular stimulation movements leftward,and that this remapping can be mproves extrapersonal neglect.Presumably,ves useful in rehabilitation (Rossetti et al..1998). tibular inputs influence visual and spatial atten- tion in complex ways.Vestibular stimulation can Psvchophvsics.Attention also improve contralesional somatosensory aware and Perception in Neglect ness (Vallar.Bottini.Rusconi.Sterzi.1993) and may transiently improve anosognosia as well What is the relationship between the magnitude of (Cappa.Sterzi.Guiseppe.Bisiach.1987).Spatial stimuli and the magnitude of patients'representa- attention may also be influenced by changes in tions of these stimuli?This question features promi- posture.which are presumably mediated by otolith nently in psychophysical studies dating back to the vestibular inputs (Mennemeier et al..1994) seminal work of Gustav Fechner in the nineteenth Similarly,proprioceptive inputs from neck muscles century (Fechner.1899).How do we understand can influence spatial attention (karnath.sievering the kinds of spatial distortions (Anderson.1996 Fetter,1994:Karath,Schenkel,Fischer,1991) Karnath Ferber.1999:Milner Harvey,1995) and serve to anchor viewer-centered referenc and "anisometries"(Bisiach Ricci Modona frames to an individual's trunk. 1998b)shown in the pe ception of neglect patients? Recent studies of patients with tactile extinc It turns out that pati ents are not always aware of tion have also focused on cross. modal factors in the same n on of space.Nor are they always awareness.Visual input when close to the loca aware of th quantity of stimuli.Rather tion of tactile stimulation may improve contra their awareness is sy stematically related to the lesional tactile awareness (di Pelleg rino Basso antity of stimuli esented (Chatterjee et al. Frassinetti.1998:Ladavas.Di Pelleg 1992b. Zeloni.1998:Vaishnavi iet al 1999)Sin ilarly the The evidence that neglect patients are systemati intention to move may also improve contralesiona cal the magnitude of the stimuli (Mennemeier et al., 1994; Pizzamiglio, Vallar, & Doricchi, 1997). Several reports demonstrate that neglect may occur in any of these reference frames (Behrmann, Moscovitch, Black, & Mozer, 1994; Chatterjee, 1994; Driver & Halligan, 1991; Farah, Brun, Wong, Wallace, & Carpenter, 1990; Hillis & Caramazza, 1995; Ladavas, 1987), suggesting that spatial attention operates across these different reference frames. Cross-Modal and Sensorimotor Integration of Space Humans have a coherent sense of space in which they perceive objects and act (Driver & Spence, 1998). Neglect studies suggest that multiple spatial representations are embedded within this sense of space. Presumably, multiple sensory modalities interact in complex ways to give rise to multiple representations of space. Rubens and colleagues (Rubens, 1985) de￾monstrated that left-sided vestibular stimulation improves extrapersonal neglect. Presumably, ves￾tibular inputs influence visual and spatial atten￾tion in complex ways. Vestibular stimulation can also improve contralesional somatosensory aware￾ness (Vallar, Bottini, Rusconi, & Sterzi, 1993) and may transiently improve anosognosia as well (Cappa, Sterzi, Guiseppe, & Bisiach, 1987). Spatial attention may also be influenced by changes in posture, which are presumably mediated by otolith vestibular inputs (Mennemeier et al., 1994). Similarly, proprioceptive inputs from neck muscles can influence spatial attention (Karnath, Sievering, & Fetter, 1994; Karnath, Schenkel, & Fischer, 1991) and serve to anchor viewer-centered reference frames to an individual’s trunk. Recent studies of patients with tactile extinc￾tion have also focused on cross-modal factors in awareness. Visual input when close to the loca￾tion of tactile stimulation may improve contra￾lesional tactile awareness (di Pellegrino, Basso, & Frassinetti, 1998; Ladavas, Di Pellegrino, Farne, & Zeloni, 1998; Vaishnavi et al., 1999). Similarly, the intention to move may also improve contralesional tactile awareness (Vaishnavi et al., 1999). Since patients with neglect may have personal neglect (Bisiach et al., 1986) or a deficit of their own body schema (Coslett, 1998), the question of how body space is integrated with extrapersonal space also arises. Tactile sensations are experienced as being produced by an object touching the body, an as￾pect of peripersonal space. Visual sensations are experienced as being produced by objects at a dis￾tance from the body, in extrapersonal space. The integration of tactile and visual stimulation may contribute to the coordination of extrapersonal and peripersonal space (Vaishnavi, Calhoun, & Chatterjee, 2001). Guiding movements by vision also involves integrating visual signals for movement. This visual-motor mapping can be altered if a subject wears prisms that displace stimuli to the left or right of their field of view. Recent work suggests that patients with neglect who are wearing prisms that displace visual stimuli to their right remap ballistic movements leftward, and that this remapping can be useful in rehabilitation (Rossetti et al., 1998). Psychophysics, Attention, and Perception in Neglect What is the relationship between the magnitude of stimuli and the magnitude of patients’ representa￾tions of these stimuli? This question features promi￾nently in psychophysical studies dating back to the seminal work of Gustav Fechner in the nineteenth century (Fechner, 1899). How do we understand the kinds of spatial distortions (Anderson, 1996; Karnath & Ferber, 1999; Milner & Harvey, 1995) and “anisometries” (Bisiach, Ricci, & Modona, 1998b) shown in the perception of neglect patients? It turns out that patients are not always aware of the same proportion of space. Nor are they always aware of the same quantity of stimuli. Rather, their awareness is systematically related to the quantity of stimuli presented (Chatterjee et al., 1992b). The evidence that neglect patients are systemati￾cally influenced by the magnitude of the stimuli Anjan Chatterjee 10