78 BARRETT, EDMONDSON-JONES, HALL within normal limits, although the shallow function indi- cated a general loss of temporal acuity. In the visual TOJ, F.D.’s data revealed a large spatiotemporal bias against the contralesional object. This is consistent with prior entry models of neglect and extinction, which attribute spatiotemporal deficits to a disruption in the competitive interactions between ipsi- and contralesional stimuli (Di Pellegrino et al., 1997; Karnath et al., 2002; Rorden et al., 1997). F.D.’s data, therefore, reveal an association between visual and auditory deficits on one task (extinction) and a clear dissociation between visual and auditory deficits on another (TOJ). Data for J.B. also reveal a dissociation between the extinction and TOJ tasks. In this patient, intact performance on the vis- ual and auditory extinction tasks contrasts with a multi- modal deficit in the TOJ for the same objects presented to the same location. The pattern of dissociations above caution against the assumption that the same test presented in different modalities will tap identical attentional resources. Previ- ous studies comparing associations between visual and auditory attentional bias using extinction and TOJ tasks have found conflicting results (e.g., Eramudugolla et al., 2007; Sinnett et al., 2007) and highlight the variability typically observed in comparisons of visual and audi- tory inattention using different measures. The use of vis- ual and auditory stimuli precisely matched in their spatial and temporal parameters in this study suggests that this variation is attributable to the way individual patterns of impairment disrupt spatial and temporal selection in particular tasks rather than to confounds associated with the presentation of stimuli in each modality to different (intracranial and extrapersonal) locations (e.g., Sinnett et al., 2007). The strength of association between visual and auditory deficits in our patients depends upon whether the presentation of stim- uli is simultaneous or asynchronous. Recent evidence from transcranial magnetic stimulation studies has revealed modality-specific substrates of visual and audi- tory time perception (Bueti, Bahrami, & Walsh, 2008). Spatial and temporal deficits in neglect and extinction often coincide (Becchio & Berone, 2006; Danckert et al., 2007), and it is likely that associations between visual and auditory deficits will reflect the contribution of these to task performance in each modality. In audition, temporal asynchronies have been shown to be a power- ful determinant of scene segregation. Common onsets provide a cue for grouping while asynchronous onsets promote stimulus segregation (e.g., Hukin & Darwin, 1995). This temporal segregation is thought to occur prior to localization (Hill & Darwin, 1996; Woods & Colburn, 1992) and would have provided a nonspatial mechanism for segregating sounds in the TOJ but not the extinction task. Asking respondents to report the identity rather than the position of the first target in the TOJ task might have accentuated this nonspatial effect, distinguishing our data from evidence of an ipsilesional bias in TOJ for auditory targets identified by their spa- tial location (Eramudugolla et al., 2007; Karnath et al., 2002). Task-dependent variability in the effect of audi- tory spatial cues has previously been reported by McDonald and Ward (1999) and has been interpreted as evidence for mechanisms of auditory attention that operate independently of spatial location. This can be contrasted with the obligatory role of spatial informa- tion in delimiting object boundaries in the visual system (Baylis & Driver, 1993; Kim & Cave, 2001; Kramer, Weber, & Watson, 1997; Lamy & Tsal, 2000) and pro- vides a potential account for the (relative and absolute) dissociation of visual and auditory TOJs in our patients. An important implication of this account is that the assumption of equivalence that has informed much of the research investigating visual and auditory atten- tional biases inadequately describes modality-specific variation in the contribution of spatial information to performance on measures of neglect and extinction. In conclusion, the current results suggest that associa- tions between visual and auditory attentional deficits can occur but these are neither obligatory nor pervasive. Associations varied within patients and across tasks and were apparent despite the use of visual and auditory stimuli that were precisely matched in their spatial and temporal parameters. An important implication of this result is that measures of association between visual and auditory inattention will vary according to the type of task involved and the extent that performance in each modality is mediated by spatial information. This argues against the characterization of attention as either a uni- modal or a supramodal resource and instead supports a more complex model of task-specific impairment that may vary across modalities in neglect. Research has revealed both unimodal and multimodal responses to spatial information across a distributed network of corti- cal areas (Bushara, Weeks, Ishii, Catalan, & Tian, 1999; Lewis et al., 2000; Macaluso, Frith, & Driver, 2000), with neurons responding to spatially convergent input from different modalities found in the superior temporal and intraparietal sulci as well as the prefrontal cortices (Beauchamp, 2005; Gifford & Cohen, 2004; Maier, Neu- hoff, Logothetis, & Ghazanfar, 2004). Neglect symptoms can arise from damage to many different cortical and subcortical regions (Coulthard, Parton, & Husain, 2007; Halligan, Fink, Marshall, & Vallar, 2003; Vallar, 2001), and it is likely that individual patterns of impairment will reflect the contribution of these to different levels of spa- tial description (Ghazanfar & Schroeder, 2006; Karnath, 2001; Marshall, Halligan, & Robertson, 1993; Mesulam, 1981). Accordingly the type of deficit observed when this distributed system is compromised will depend on the site and extent of the causal lesion as well as the nature of spa- tial representation required by the task. By using matched tasks to explore the manifestation of these deficits across different sensory modalities, confounds associated with different measures of performance can be reduced. This approach supplements evidence from existing investiga- tions of neglect and extinction in order to specify more pre- cisely the way spatial selection operates across different sensory modalities and tasks. Original manuscript received 2 December 2008 Revised manuscript accepted 19 February 2009 First published online 29 May 2009