Revisiting Previously Searched Locations in Visual Neglect: Role of Right Parietal and Frontal Lesions in Misjudging Old Locations as New

Abstract

Right-hemisphere patients with left neglect often demonstrate abnormal visual search, re-examining stimuli to the right while ignoring those to the left. But re-fixations alone do not reveal if patients misjudge whether they have searched a location before. Here, we not only tracked the eye movements of 16 neglect patients during search, but also asked them to click a response button only when they judged they were fixating a target for the very first time. ''Re-clicking'' on previously found targets would indicate that patients erroneously respond to these as new discoveries. Lesions were mapped with high-resolution MRI. Neglect patients with damage involving the right intraparietal sulcus or right inferior frontal lobe ''re-clicked'' on previously found targets on the right at a pathological rate, whereas those with medial occipito-temporal lesions did not. For the intraparietal sulcus patients, the probability of erroneous re-clicks on an old target increased with time since first discovering it; whereas for frontal patients it was independent of search time, suggesting different underlying mechanisms in these two types of patient. Re-click deficits correlated with degree of leftward neglect, mainly due to both being severe in intraparietal cases. These results demonstrate that misjudging previously searched locations for new ones can contribute to pathological search in neglect, with potentially different mechanisms being involved in intraparietal versus inferior frontal patients. When combined with a spatial bias to the right, such deficits might explain why many neglect patients often re-examine rightward locations, at the expense of items to their left.

Continuous ASL perfusion fMRI investigation of higher cognition: Quantification of tonic CBF changes during sustained attention and working memory tasks

“…Sustained attention tasks used in most previous studies had strong working memory components, such as updating consecutive digits (Coull et al, 1996;Lawrence et al, 2003) or counting certain types of events (Pardo et al, 1991). If parietal activation in those studies reflected maintenance processes of working memory (e.g., Jonides et al, 1998;Mannan et al, 2005;Ravizza et al, 2005), lack of parietal activation in the present study may be due to the fact that our visual target detection task required minimal working memory load.…”

Rapid Formation of Spatiotopic Representations As Revealed by Inhibition of Return

“…In such a task, patients typically refixate visited targets in their supposedly intact right visual field much more frequently than healthy controls (Husain et al, 2001;Mannan et al, 2005). Indeed, Mannan et al (2005) suggested that "difficulties in keeping track of previously inspected targets (because of impaired transsaccadic remapping and/or memory) may be one contributing component to visual neglect . .…”

Convergence between Lesion-Symptom Mapping and Functional Magnetic Resonance Imaging of Spatially Selective Attention in the Intact Brain

“…Other spatial-attentional processes seen in neglect patients, such as deficits in spatial working memory (Malhotra et al, 2005;Mannan et al, 2005), in gaze-centric spatial remapping (Vuilleumier et al, 2007) or in stimulus-driven reorienting (Corbetta et al, 2000;Kincade et al, 2005), may relate to other parietal localizations (e.g., more inferiorly). Impaired performance on clinical tests such as target cancellation most likely results from a combination of different attentional deficits within the same patient (Malhotra et al, 2005;Mannan et al, 2005;Nachev and Husain, 2006).…”