A non-spatial bias favouring fixated stimuli revealed in patients with spatial neglect

Abstract

The cardinal feature of spatial neglect is severely impaired exploration of the contralesional space, a failure resulting in unawareness of many contralesional stimuli. This deficit is exacerbated by a reflexive attentional bias toward ipsilesional items. Here we show that, in addition to these spatially lateralized failures, neglect patients also exhibit a severe bias favouring stimuli presented at fixation. We tested neglect patients and matched healthy and right-hemisphere damaged patients without neglect in a task requiring saccade execution to targets in the left or right hemifield. Targets were presented alone or simultaneously with a distracter that appeared in the same hemifield, in the opposite hemifield, or at fixation. We found two fundamental biases in saccade initiation of neglect patients: irrelevant distracters presented in the preserved hemifield tended to capture gaze reflexively, resulting in a large number of saccades erroneously directed toward the distracter. Additionally, distracters presented at fixation severely disrupted saccade initiation irrespective of saccade direction, leading to disproportionately increased latencies of left and right saccades. This latency increase was specific to oculomotor responses of neglect patients and was not observed when a manual response was required. These results show that, in addition to their failure to inhibit reflexive glances toward ipsilesional items neglect patients exhibit a strong oculomotor bias favouring fixated stimuli. We conclude that impaired initiation of saccades in any direction contributes to the deficits of spatial exploration that characterize spatial neglect.

Exploring the world with Bálint syndrome: biased bottom-up guidance of gaze by local saliency differences

“…similar durations were observed in a previous study when a simultanagnosic patient was required to make saccades to peripheral targets while a central fixation stimulus was present (a so-called overlap task; Nyffeler et al 2005). however, the sudden appearance of a stimulus at fixation also strongly affects fixation durations in patients with unilateral posterior brain damage and spatial neglect (Ptak et al 2007;Walker and Findlay 1996), while the prolonged durations during visual scanning appear to be specific to Bálint syndrome. how can 'sticky' fixation during ocular exploration be explained?…”

Visual exploration pattern in hemineglect

“…For the number of saccades made during free exploration, we found direction-speciWc eVects: the number of saccades was signiWcantly reduced for leftward saccades and signiWcantly increased for rightward saccades. Studies in neglect patients examining saccade planning towards unilaterally presented visual targets reported signiWcantly decreased amplitude of contralesional saccades, but unaVected ipsilesional saccades (Heide & Kömpf, 1998;Ptak, Schnider, Golay, & Müri, 2007;Walker & Findlay, 1996). Furthermore, neglect patients are often slower to initiate contralesional saccades or making small, multistep saccades (Walker & Findlay, 1996;Behrmann, Ghiselli-Crippa & Dimatteo, 2001).…”

The Dorsal Attention Network Mediates Orienting toward Behaviorally Relevant Stimuli in Spatial Neglect

“…All patients had preserved visual fields for the central ϳ20°as assessed with computerized perimetry testing (white dot presented on black background at positions ranging between Ϫ25 and ϩ25 degrees) and/or clinical confrontation. All neglect patients manifested behavioral signs of left unawareness (e.g., failure to notice objects or persons placed on their left, difficulties with dressing or grooming) and lateralized failures in the following neglect tests: Bells cancellation (Gauthier et al, 1989), cancellation of inverted Ts (Ptak et al, 2007), line bisection (Schenkenberg et al, 1980), sentence copying (Wilson et al, 1987), and copying a landscape. Participants had similar age (ANOVA across all four groups, F (3,36) ϭ 0.44), and the three patient groups had comparable time since injury (F (2,27) ϭ 0.45).…”