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Hierarchical processing in Balint's syndrome: a failure of flexible top-down attention.

Mevorach C, Shalev L, Green RJ, Chechlacz M, Riddoch MJ, Humphreys GW - Front Hum Neurosci (2014)

Bottom Line: We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter.However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter.We conclude that in Balint' s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

View Article: PubMed Central - PubMed

Affiliation: Behavioural Brain Sciences Centre, School of Psychology, University of Birmingham Birmingham, UK.

ABSTRACT
Patients with Balint' s syndrome are typically impaired at perceiving multiple objects simultaneously, and at evaluating the relationship between multiple objects in a scene (simultanagnosia). These deficits may not only be observed in complex scenes, but also when local elements of individual objects must be integrated into a perceptual global whole. Thus, unlike normal observers, patients with simultanagnosia typically show a bias towards the local forms, even to the extent that they cannot identify the global stimuli. However, we have previously shown that global processing is still attainable in Balint patients in certain scenarios (e.g., when local elements are unfamiliar). This suggests that in addition to a possible perceptual deficit that favors the local elements in these patients, impaired attentional control may be at the core of their unique performance. To test this hypothesis we manipulated the perceptual saliency of the local and global elements in a compound letter task so that it included global-more-salient or local-more-salient displays. We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter. However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter. We conclude that in Balint' s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

No MeSH data available.


Example of the compound letters that were used in the present study incorporating global-more-salient and local-more-salient displays. The levels of each stimulus could be congruent (where local and global letters matched) or incongruent (where local and global letters differed).
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Figure 3: Example of the compound letters that were used in the present study incorporating global-more-salient and local-more-salient displays. The levels of each stimulus could be congruent (where local and global letters matched) or incongruent (where local and global letters differed).

Mentions: The stimuli were presented on a 17-in. monitor (1024 × 768 pixels) of a laptop. The viewing distance was approximately 60 cm so that each centimeter on the screen represented 0.968 of visual angle. All the stimuli appeared against a black background. Two sets of displays were used to represent high global saliency and high local saliency. For the condition with relatively high local saliency, the compound stimuli were created from orthogonal combinations of the letters H and S. Each compound contained both red and white local letters (see Figure 3). Each local letter subtended 1.348 × 1.068 of visual angle (in width and height, respectively) and the global letter subtended 8.268 × 5.388 of visual angle (in width and height, respectively). The inter-element distance was 0.388 of visual angle. In the condition with relatively high global saliency, the compound letters were again composed of the letters H and S, which were combined orthogonally at the local and global levels. All the local letters were red. Each local letter subtended 1.348 × 1.068 of visual angle (in width and height, respectively) and the global letter subtended 5.668 × 4.518 of visual angle (in width and height, respectively). The distance between local elements was 0.0968 of visual angle. These letters underwent a blur procedure in Paint Shop Pro 7.0 with factor = 7. The compound letters appeared at the center of the screen. A white asterisk (0.578), also presented at the center of the screen, served as fixation.


Hierarchical processing in Balint's syndrome: a failure of flexible top-down attention.

Mevorach C, Shalev L, Green RJ, Chechlacz M, Riddoch MJ, Humphreys GW - Front Hum Neurosci (2014)

Example of the compound letters that were used in the present study incorporating global-more-salient and local-more-salient displays. The levels of each stimulus could be congruent (where local and global letters matched) or incongruent (where local and global letters differed).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3936250&req=5

Figure 3: Example of the compound letters that were used in the present study incorporating global-more-salient and local-more-salient displays. The levels of each stimulus could be congruent (where local and global letters matched) or incongruent (where local and global letters differed).
Mentions: The stimuli were presented on a 17-in. monitor (1024 × 768 pixels) of a laptop. The viewing distance was approximately 60 cm so that each centimeter on the screen represented 0.968 of visual angle. All the stimuli appeared against a black background. Two sets of displays were used to represent high global saliency and high local saliency. For the condition with relatively high local saliency, the compound stimuli were created from orthogonal combinations of the letters H and S. Each compound contained both red and white local letters (see Figure 3). Each local letter subtended 1.348 × 1.068 of visual angle (in width and height, respectively) and the global letter subtended 8.268 × 5.388 of visual angle (in width and height, respectively). The inter-element distance was 0.388 of visual angle. In the condition with relatively high global saliency, the compound letters were again composed of the letters H and S, which were combined orthogonally at the local and global levels. All the local letters were red. Each local letter subtended 1.348 × 1.068 of visual angle (in width and height, respectively) and the global letter subtended 5.668 × 4.518 of visual angle (in width and height, respectively). The distance between local elements was 0.0968 of visual angle. These letters underwent a blur procedure in Paint Shop Pro 7.0 with factor = 7. The compound letters appeared at the center of the screen. A white asterisk (0.578), also presented at the center of the screen, served as fixation.

Bottom Line: We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter.However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter.We conclude that in Balint' s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

View Article: PubMed Central - PubMed

Affiliation: Behavioural Brain Sciences Centre, School of Psychology, University of Birmingham Birmingham, UK.

ABSTRACT
Patients with Balint' s syndrome are typically impaired at perceiving multiple objects simultaneously, and at evaluating the relationship between multiple objects in a scene (simultanagnosia). These deficits may not only be observed in complex scenes, but also when local elements of individual objects must be integrated into a perceptual global whole. Thus, unlike normal observers, patients with simultanagnosia typically show a bias towards the local forms, even to the extent that they cannot identify the global stimuli. However, we have previously shown that global processing is still attainable in Balint patients in certain scenarios (e.g., when local elements are unfamiliar). This suggests that in addition to a possible perceptual deficit that favors the local elements in these patients, impaired attentional control may be at the core of their unique performance. To test this hypothesis we manipulated the perceptual saliency of the local and global elements in a compound letter task so that it included global-more-salient or local-more-salient displays. We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter. However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter. We conclude that in Balint' s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

No MeSH data available.