Regular articleRight hemisphere control of visuospatial attention: line-bisection judgments evaluated with high-density electrical mapping and source analysis☆☆
Introduction
Line-bisection tasks are a commonly used metric for the clinical assessment of visuospatial neglect syndrome, a condition that predominantly results from vascular lesions to the right inferior parietal or temporoparietal cortex (e.g., Vallar et al 1987, Cappa et al 1991, Mesulam 2000, Na et al 2000, Kerkhoff 2001; see Karnath, 2001 for a comprehensive treatment). Patients with visuospatial neglect syndrome generally bisect lines significantly to the right of veridical center (Robertson and Halligan, 1999), due either to a decrement in the ability to allocate attention to left visual space or to hyperattention to rightward space. Clinical findings from neglect patients allied to the scores of neuroimaging studies showing a predomination of right parietal activity during tasks requiring visuospatial attention (e.g., Corbetta et al 2000, Coull et al 2001 have led to the formulation that while both left and right parietal areas are involved in attention to the right visual field, right parietal areas alone may control attention to the left visual hemifield (e.g., Heilman and van den Abell 1980, Weintraub and Mesulam 1987. A measure of support for this conjecture is derived from the finding that neurologically normal subjects demonstrate a phenomenon known as “pseudoneglect” (Bowers and Heilman, 1980), in which a significant and systematic misbisection of lines (or space) occurs that is leftward of veridical center. This leftward tendency in normal observers has been theorized to result from a profound parietal asymmetry in attentional control, which gives rise to some degree of hyper-attentiveness to the left visual field (in space-based attention), or to the left-hand side of individual objects (in object-based attention) (see Jewell and McCourt 2000, McCourt 2001, McCourt and Jewell 1999, McCourt et al 2000.
Functional imaging (fMRI) studies have confirmed a central role for right parietal cortices in performance of both line-bisection tasks Weiss et al 2000, Fink et al 2000a, Fink et al 2000b, Fink et al 2001, Fink et al 2002, Galati et al 2000 and judgments of object location relative to the midsagittal plane Vallar et al 1999, Galati et al 2000. There have, to date, been no electrophysiological investigations of line bisection; consequently the timing of right parietal involvement relative to the timing of ongoing stimulus processing is as yet unknown. In the current study, we performed high-density electrical mapping (from 128 scalp electrodes) of the visual event-related potential (ERP) while subjects engaged in either a tachistoscopic forced-choice line-bisection task (McCourt and Olafson, 1997) or a control task in which they simply judged whether or not lines were transected. Our main objectives were to both confirm the involvement of and define the timecourse of right parietal activity in performance of the line-bisection task. In particular, we wished to assess the relationship of parietal attentional processes in the dorsal visual processing stream to the processing of the line stimuli by object recognition areas of the ventral visual stream. An open question is whether line midpoint judgments can only be made upon completion of object recognition processes for the object that is to be bisected. In the present study, we systematically varied the timing of object-recognition processes by varying the contrast level at which lines were displayed. We used the well-characterized N1 component of the visual evoked potential (VEP) as an index of the timing of object recognition processes, since this component has repeatedly been shown to be correlated with the processes involved in object recognition (e.g., Allison et al 1999, Bentin et al 1999, Doniger et al 2000, Doniger et al 2001. Systematically varying the latency of this component allowed us to assess whether bisection processes tracked this latency manipulation.
Section snippets
Subjects
Nine (4 male) neurologically normal, paid volunteers (ages 19–45 years, mean = 29.2 years) participated. All subjects provided written informed consent, and the Institutional Review Boards of the Nathan Kline Research Institute and North Dakota State University approved all procedures. All subjects possessed normal or corrected-to-normal vision and were right-handed, as measured using the Oldfield (1971) laterality inventory (mean score = 58.3, SD = 22.7).
Instrumentation and stimuli
Subject responses were sensed and
Behavioural results
Fig. 2 presents group-averaged psychometric functions obtained in the Line-Bisection condition at each level of line contrast. Open symbols plot the mean percentage “left” responses (± 1 SEM) against transector location (in degrees relative to veridical line midpoint). The data are well behaved, and the range of transector locations sampled is observed to encompass perceived line midpoint in this sample of subjects. Solid lines depict cumulative Gaussian distributions fitted to the data by
Discussion
The current findings explicate the brain mechanisms underlying performance of the visual line-bisection task, a perceptual version of the perceptual-motor task that is frequently employed in the clinic to disclose the presence and severity of visuospatial neglect syndrome. We define an electrophysiological correlate of line-bisection judgments, which manifests as a right parieto-occipital negative potential that is significantly earlier in latency and larger in magnitude than that over left
Acknowledgements
We express our sincere appreciation to Deirdre Foxe, Beth Higgins, and Dr. Micah Murray for their technical help with this study. We are most grateful to Dr. Gereon Fink and his colleagues for generously allowing us to reproduce their fMRI data in the current report. Dr. Antigona Martinez provided valuable comments on an earlier version of the manuscript for which we are indebted to her. Our thanks also go to two anonymous reviewers for their careful and constructive comments. This work was
References (88)
- et al.
Pseudoneglecteffects of hemispace on a tactile line bisection task
Neuropsychologia
(1980) - et al.
Left visuo-spatial neglect can be worse in far than in near space
Neuropsychologia
(1994) - et al.
Disordered sensorimotor transformations for reaching following posterior cortical lesions
Neuropsychologia
(2001) - et al.
Concurrent processing streams in monkey visual cortex
Trends Neurosci
(1988) - et al.
Visual perceptual learning in human object recognition areasa repetition priming study using high-density electrical mapping
NeuroImage
(2001) - et al.
‘Where’ depends on ‘what’a differential functional anatomy for position discrimination in one- versus two-dimensions
Neuropsychologia
(2000) - et al.
Task instructions influence the cognitive strategies involved in line bisection judgmentsevidence from modulated neural mechanisms revealed by fMRI
Neuropsychologia
(2002) - et al.
Pseudoneglecta review and meta-analysis of performance factors in line bisection tasks
Neuropsychologia
(2000) Spatial hemineglect in humans
Prog. Neurobiol
(2001)- et al.
Putting spatial attention on the maptiming and localization of stimulus selection processes in striate and extrastriate visual areas
Vision Res
(2001)
Performance consistency of normal observers in forced-choice tachistoscopic visual line bisection
Neuropsychologia
The influence of unimanual response on pseudoneglect magnitude
Brain Cogn
Stimulus modulation of pseudoneglecteffect of line geometry
Neuropsychologia
Visuospatial attention in line bisectionstimulus modulation of pseudoneglect
Neuropsychologia
Cognitive and perceptual influences on visual line bisectionpsychophysical and chronometric analyses of pseudoneglect
Neuropsychologia
Electric source imaging of human brain functions
Brain Res. Brain Res. Rev
Ipsilesional versus contralesional neglect depends on attentional demands
Cortex
The assessment and analysis of handednessthe Edinburgh Inventory
Neuropsychologia
Contributions of object- and space-based mechanisms to line bisection errors
Neuropsychologia
Coding of image contrast in central visual pathways of the macaque monkey
Vision Res
Cat and monkey retinal ganglion cells and their functional roles
Trends Neurosci
The anatomy of unilateral neglect after right-hemisphere stroke lesions. A clinical/CT-scan correlation study in man
Neuropsychologia
Electrophysiological studies of human face perception. I. Potentials generated in occipitotemporal cortex by face and non-face stimuli
Cereb. Cortex
Spatial reference frames and hemispatial neglect
ERP manifestations of processing printed words at different psycholinguistic levelstime course and scalp distribution
J. Cogn. Neurosci
Perceptual and premotor factors of unilateral neglect
Neurology
Dysfunction of early-stage visual processing in schizophrenia
Am. J. Psychiatr
Computed tomography correlates of chronic unilateral neglect
Neuropsychology
Voluntary orienting is dissociated from target detection in human posterior parietal cortex
Nature Neurosci
The noradrenergic α2 agonist clonidine modulates behavioural and neuranotomical correlates of human attentional orienting and alerting
Cereb. Cortex
Activation time-course of ventral visual stream object-recognition areashigh density electrical mapping of perceptual closure processes
J. Cogn. Neurosci
Object centered visual neglect, or relative egocentric neglect?
J. Cogn. Neurosci
Contralateral neglect induced by right posterior parietal rTMS in healthy subjects
Neuroreport
Timing of right parietal and frontal cortex activity in visuo-spatial perceptiona TMS study in normal individuals
Neuroreport
Line bisection judgments implicate right parietal cortex and cerebellum as assessed by fMRI
Neurology
The neural basis of vertical and horizontal line bisection judgmentsan fMRI study of normal volunteers
NeuroImage
Early visual processing deficits in schizophreniaimpaired P1 generation revealed by high-density electrical mapping
Neuroreport
Parieto-occipital ∼ 10 Hz activity reflects anticipatory state of visual attention mechanisms
Neuroreport
Timecourse of activation flow from V1 to frontal cortex in humansa framework for defining “early” visual processing
Exp. Brain Res
Attention-dependent suppression of distracter visual input can be cross-modally cued as indexed by anticipatory parieto-occipital alpha-band oscillations
Cogn. Brain Res
An improved boundary element method for realistic volume-conductor modeling
IEEE Trans. Biomed. Eng
The neural basis of egocentric and allocentric coding of space in humansa functional magnetic resonance study
Exp. Brain Res
Visual properties of neurons in inferotemporal cortex of the Macaque
J. Neurophysiol
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Supplementary data associated with this article can be found at doi: 10.1016/S1053-8119(03)00057-0.