Task-related modulation of visual neglect in cancellation tasks

Abstract

Unilateral neglect involves deficits of spatial exploration and awareness that do not always affect a fixed portion of extrapersonal space, but may vary with current stimulation and possibly with task demands. Here, we assessed any 'top-down', task-related influences on visual neglect, with novel experimental variants of the cancellation test. Many different versions of the cancellation test are used clinically, and can differ in the extent of neglect revealed, though the exact factors determining this are not fully understood. Few cancellation studies have isolated the influence of top-down factors, as typically the stimuli are changed also when comparing different tests. Within each of three cancellation studies here, we manipulated task factors, while keeping visual displays identical across conditions to equate purely bottom-up factors. Our results show that top-down task-demands can significantly modulate neglect as revealed by cancellation on the same displays. Varying the target/non-target discrimination required for identical displays has a significant impact. Varying the judgement required can also have an impact on neglect even when all items are targets, so that non-targets no longer need filtering out. Requiring local versus global aspects of shape to be judged for the same displays also has a substantial impact, but the nature of discrimination required by the task still matters even when local/global level is held constant (e.g. for different colour discriminations on the same stimuli). Finally, an exploratory analysis of lesions among our neglect patients suggested that top-down task-related influences on neglect, as revealed by the new cancellation experiments here, might potentially depend on right superior temporal gyrus surviving the lesion.

Spatio-Temporal Features of Visual Exploration in Unilaterally Brain-Damaged Subjects with or without Neglect: Results from a Touchscreen Test

“…These gradient indexes can be considered in close connection with published scientific works in which a gradient of the omission rate has been experimentally evidenced in neglect patients [18], [29], [30]–[31]. In those works, the display of a cancellation test was divided into 6 to 8 equal vertical columns, each characterized by a given omission rate which almost linearly increased moving controlesionally.…”

Dynamic attentional modulation of vision across space and time after right hemisphere stroke and in ageing

“…However, when central load was increased, responses to checkerboards presented to the left visual field were reduced or abolished (see also, Bonato et al. (2010); Peers et al., 2006; Sarri et al., 2009). Russell et al.…”

Inappropriate usage of the Brunner–Munzel test in recent voxel-based lesion-symptom mapping studies

“…Unfortunately, some of these papers (e.g. Coulthard et al , 2008a; Coulthard et al , 2008b; Malhotra et al , 2009; Molenberghs et al , 2008; Moro et al , 2008; Pazzaglia et al , 2008a; Pazzaglia et al , 2008b; Rossit et al , 2009; Sarri et al , 2009; Zihl et al , 2009) report results that are almost certainly due to the lack of appropriate procedures for infrequently lesioned voxels. These results may be critically flawed, and we therefore suggest that these papers (and any others that have been affected) be re-analyzed and revised using either the permutation generated test scores as implemented in the current version of NPM, or using other statistical tests (e.g.…”