Positron emission tomography (PET) was used to identify the neural systems involved in shifting spatial attention to visual stimuli in the left or right visual field along foveofugal or foveocentric directions. Psychophysical evidence indicated that stimuli at validly cued locations were responded to faster than stimuli at invalidly cued locations. Reaction times to invalid probes were faster when they were presented in the same than in the opposite direction of an ongoing attention movement. PET evidence indicated that superior parietal and superior frontal cortex were more active when attention was shifted to peripheral locations than when maintained at the center of gaze. Both regions encoded the visual field and not the direction of an attention shift. In the right superior parietal lobe, two distinct responses were localized for attention to left and right visual field. Finally, the superior parietal region was active when peripheral locations were selected on the basis of cognitive or sensory cues independent of the execution of an overt response. The frontal region was active only when responses were made to stimuli at selected peripheral locations. These findings indicate that parietal and frontal regions control different aspects of spatial selection. The functional asymmetry in superior parietal cortex may be relevant for the pathophysiology of unilateral neglect.

A PET study of visuospatial attention

The syndrome of contralesional neglect reflects a lateralized disruption of spatial attention. In the human, the left hemisphere shifts attention predominantly in the contralateral hemispace and in a contraversive direction whereas the right hemisphere distributes attention more evenly, in both hemispaces and both directions. As a consequence of this asymmetry, severe contralesional neglect occurs almost exclusively after right hemisphere lesions. Patients with left neglect experience a loss of salience in the mental representation and conscious perception of the left side and display a reluctance to direct orientating and exploratory behaviours to the left. Neglect is distributed according to egocentric, allocentric, world-centred, and object-centred frames of reference. Neglected events can continue to exert an implicit influence on behaviour, indicating that the attentional filtering occurs at the level of an internalized representation rather than at the level of peripheral sensory input. The unilateral neglect syndrome is caused by a dysfunction of a large-scale neurocognitive network, the cortical epicentres of which are located in posterior parietal cortex, the frontal eye fields, and the cingulate gyrus. This network coordinates all aspects of spatial attention, regardless of the modality of input or output. It helps to compile a mental representation of extrapersonal events in terms of their motivational salience, and to generate 'kinetic strategies' so that the attentional focus can shift from one target to another.

/pdf/spatial-attention-and-neglect-parietal-frontal-and-cingulate-3urebfqlps.pdf

Spatial attention and neglect: parietal, frontal and cingulate contributions to the mental representation and attentional targeting of salient extrapersonal events.

Space- and object-based attention components were examined in neurologically normal and parietal-lesion subjects, who detected a luminance change at 1 of 4 ends of 2 outline rectangles. One rectangle end was precued (75% valid); on invalid-cue trials, the target appeared at the other end of the cued rectangle or at 1 end of the uncued rectangle. For normals, the cost for invalid cues was greater for targets in the uncued rectangle, indicating an object-based component. Both right- and left-hemisphere patients showed costs that were greater for contralesional targets. For right-hemisphere patients, the object cost was equivalent for contralesional and ipsilesional targets, indicating a spatial deficit, whereas the object cost for left-hemisphere patients was larger for contralesional targets, indicating an object deficit.

http://psych.utoronto.ca/users/ferber/teaching/visualattention/readings/Oct13/1994_Egly_etal_JEPG.pdf

Shifting visual attention between objects and locations: evidence from normal and parietal lesion subjects.

The authors examined the question of whether a decrease in the efficiency of inhibitory processing with aging is a general phenomenon. Thirty elderly and 32 young adults performed a series of tasks from which the authors could extract measures of inhibitory function. The tasks and task components included response compatibility, negative priming, stopping, spatial precuing, Wisconsin Card Sorting Test (WCST), and the Cognitive Failures Questionnaire (CFQ). Only limited evidence for age-related differences in inhibitory function was obtained. Old adults had more difficulty than young adults in stopping an overt response and adopting new rules in a categorization task. However, elderly and young adults produced equivalent negative priming effects, response compatibility effects, spatial precuing effects, and self-reported cognitive failures. The findings are discussed in terms of the relationship between aging, inhibitory processes, and neuroanatomical and physiological function.

/pdf/aging-and-inhibition-beyond-a-unitary-view-of-inhibitory-2h9b7gg2qo.pdf

Aging and Inhibition: Beyond a Unitary View of Inhibitory Processing in Attention

https://visionlab.harvard.edu/Members/Patrick/PDF.files/CogPsychR.pdf

Frances A. Friedrich

Papers

How do the parietal lobes direct covert attention