Cross Modal Coordination of Attention

The existence of attentional selection in different modalities raises a basic question: Is there a single, supramodal attentional system that mediates selection across multiple modalities, or are there individual attentional systems for each modality that have some degree of cross talk with one another? Results from neuropsychological patients with neglect support a supramodal view of attention. Neglect patients have difficulty attending to both visual and auditory stimuli opposite the lesioned hemisphere, suggesting that parietal lobe attentional processes operate on a representation of space that codes both visual and auditory stimuli. Similar results have been reported from multimodal versions of the spatial precuing task. In the multimodal version of this task, neglect patients are asked to detect a lateralized visual stimulus. This visual target is preceded by a lateralized precue presented in either the visual or the auditory modality. Neglect patients show similar orienting behavior to both types of precues; specifically, neglect patients have difficulty disengaging attention from precues presented on the good (ipsilesional) side of peripheral space irrespective of the cue's modality. These results support a supramodal representation for parietal lobe attentional processes.

Further strengthening the supramodal view of attention, neglect patients also fail to attend to somatosensory stimuli presented on the bad (contrale-sional) side of peripheral space. However, somatosen-sory neglect could be explained by contralesional sensory deficits that accompany brain damage; inputs from the contralesional side of the body may be weaker than inputs from the ipsilesional side of the body. A convincing demonstration of somatosensory neglect was provided by testing neglect patients' ipsilesional hands, which have no sensory loss. The patients were touched simultaneously on the left and right sides of their right wrist and asked to report where they were touched. There were two key findings. First, left neglect patients failed to notice being touched on the left side of their right wrists, demonstrating that somatosensory neglect can occur in the absence of sensory deficits. Second, the attentional impairment for detecting contralesional touches occurred whether patients' hands were facing with the palm downward or facing with the palm upward. The neglect did not follow the rotation of the hands but instead remained fixed on the left side of the wrist. These results indicate that the attentional deficit did not occur in somato-sensory coordinates, such as always neglecting the thumb side of the wrist or always neglecting the left side of the body. Instead, neglect occurred in abstract spatial coordinates that represent the left and right sides of a limb independent of that limb's orientation. This "limb-centered" somatosensory neglect bears a striking similarity to the object-centered neglect observed in the visual modality: The neglected region is not necessarily defined by the patients' midline but by the midline of a stimulus (an object or a limb).

Finally, both behavioral and ERP studies with neurologically normal observers have extended the operation of selective attention across different modalities. There appear to be strong cross-modal links in spatial attention that allow observers to spatially attend a region and select stimuli occurring in different modalities. In behavioral studies, observers visually cued to one side of space detect more quickly both visual and auditory targets on the cued side of space than on the uncued side of space; this cued location advantage occurs when the modality of the target is unpredictable. Thus, spatial attention appears to operate across modalities. Behavioral studies have also attempted to decouple attentional shifts across modalities by varying the occurrences of auditory or visual targets. Can auditory spatial attention be allocated to a different region than visual spatial attention if an auditory target is expected at one location and a visual target is expected at another location? The answer to this question seems to be "no." If observers voluntarily shift auditory spatial attention to one region to detect a highly probable auditory target, visual spatial attention seems to follow. The same result holds for shifts of visual spatial attention; auditory attention will follow visual attention when visual attention is voluntarily shifted to a region to detect a highly probable visual target. ERP studies have reported similar results. For example, if observers are required to monitor a location for an infrequently occurring visual target, larger evoked responses are generated by both visual and auditory nontarget stimuli at the attended location than at the unattended location.

One caveat from the cross-modal studies of attention is that although visual and auditory attention appear to operate in concert, the effects across modalities are not equivalent to effects within a single modality. Larger attentional effects are found when the cue and target appear in the same modality than in different modalities. Such an observation cannot be explained with a strong supramodal account of spatial attention. The strong supramodal account would predict that each sensory modality could cause an equivalent shift of spatial attention, which would provide enhanced processing at the attended location across all modalities. However, cross-modal studies cannot distinguish between linked unimodal attention systems and a supramodal system that receives differ entially weighted inputs from each modality. Furthermore, a supramodal system may be an emergent property of the connections that link modality-specific attentional systems. Consistent with the multiple attentional systems in the visual modality, there are likely to be both unimodal and supramodal attentional mechanisms for the coordination of attention across sensory modalities.

Aspergers Answers Revealed

Aspergers Answers Revealed

Learn How to Help, Understand amp Cope with your Aspergers Child from a UK Chartered Educational Psychologist. Before beginning any practice relating to Aspergers it is highly recommended that you first obtain the consent and advice of a qualified health,education or social care professional.

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