Spatial cognition: evidence from visual neglect

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Abstract

Recent work on human attention and representational systems has benefited from a growing interplay between research on normal attention and neuropsychological disorders such as visual neglect. Research over the past 30 years has convincingly shown that, far from being a unitary condition, neglect is a protean disorder whose symptoms can selectively affect different sensory modalities, cognitive processes, spatial domains and coordinate systems. These clinical findings, together with those of functional neuroimaging, have increased knowledge about the anatomical and functional architecture of normal subsystems involved in spatial cognition. We provide a selective overview of how recent investigations of visual neglect are beginning to elucidate the underlying structure of spatial processes and mental representations.

Section snippets

Selective preservation of pre-attentive processes

Investigations of visual neglect have contributed to the classic debate regarding the processing locus of attentional selection 2, 6. According to the late selection view, pre-attentive analysis of the whole scene takes place up to and including initial recognition of the object. However, early selection accounts argue that only basic perceptual processing takes place pre-attentively and focal attention is necessary for object recognition. The question thus hinges on the cognitive level to

Spatial reference frames

The brain codes visual inputs with respect to some spatial frame of reference. These frames provide the basis for attributing up–down, and left–right to spatial arrays and can be based on the direction of the viewer's gaze (egocentric) and/or intrinsic characteristics of an object or its environment (allocentric) (see also Box 1):

Egocentric: Egocentric space coding (with respect to different viewer-centred frames of reference, including eye-, head-, torso-, shoulder-, arm- and hand-centred

Selective impairments of imaginal representation

Left lateralized breakdown in imaginal representations without corresponding deficits in perceptual-motor performance (and vice versa) has also been found [16]. This double dissociation challenges Kosslyn's claim that perceptual and imagery processes share the same mental operations and neural structures 16, 17.

Elucidating the neuropsychological structure of space

Although Euclidian space extends seamlessly to infinity in three dimensions, space for embodied creatures, such as ourselves, can plausibly be divided into three fundamental regions: personal space, peripersonal space, and extrapersonal space [5]. Personal space is the space of the body surface: the space on which one can feel a touch or a jab, the space within which one can comb one's hair or scratch an itch. Peripersonal space is space within arm's reach, the space in which one picks up a cup

Neuroanatomical basis of spatial neglect: lesion studies in humans

Current knowledge concerning the neuroanatomical basis of spatial unilateral neglect in humans, and, by implication, of conscious spatial representation and directed attention comes from two main sources: (1) the traditional anatomo-clinical correlation between the site of the cerebral lesion and the behavioural deficit; (2) the more recently developed temporary interference with the function of specific cerebral areas, induced by transcranial magnetic stimulation (TMS). Anatomo-clinical

Neural systems underlying spatial processing

Human functional neuroimaging highlights the importance of posterior parietal cortex (PPC) for attending to spatial locations (space-based attention) or features of visual stimuli (object-based attention) [48]. More importantly, these techniques extend the information provided by lesion studies: where neuropsychological studies are limited by large lesion sizes and remote effects, functional imaging studies allow a more detailed specification of the areas involved in the cognitive operations

Conclusions

The neuropsychological syndrome of unilateral spatial neglect has become a strong and increasingly relevant tool to dissect the functional and anatomical architecture of the systems involved in spatial cognition. There is now definite evidence that spatial cognition involves a complex set of independent, although related, systems, which are likely to have discrete neuroanatomical correlates. Recent investigations of patients with spatial neglect have clear implications for our understanding of

Acknowledgements

J.C.M. and P.W.H. are supported by the UK Medical Research Council; G.R.F. is supported by the Deutsche Forschungsgemeinschaft. G.V.'s research is being supported in part by a MIUR-Cofin Grant.

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