Increased attentional load moves the left to the right

Abstract

Introduction Unilateral brain damage can heterogeneously alter spatial processing. Very often brain-lesioned patients fail to report (neglect) items appearing within the contralesional space. Much less often patients mislocalize items' spatial position. We investigated whether a top-down attentional load manipulation (dual-tasking), known to result in contralesional omissions even in apparently unimpaired cases, might also induce spatial mislocalizations. Method Nine right-hemisphere damaged patients performed three computer-based tasks encompassing different levels of attentional load. The side of appearance of visual targets had to be reported either in isolation or while processing additional information (visual or auditory dual-task). Spatial mislocalizations (from the contralesional hemispace towards the ipsilesional -unaffected-one) were then contrasted with omissions both within and across tasks, at individual as well as at group level. Results The representation of ipsilesional targets was accurate and not affected by dual-tasking requirements. Contralesional targets were instead often omitted and, under dual-task conditions, also mislocalized by four patients. Three cases reported a significant number of left targets as appearing on the right (alloesthesia). Two of these patients perceived more targets (albeit to a wrong spatial location) under dual-than under single-task load. In a fourth patient, increased visual load resulted in synchiria, the (mis)perception of single, contralesional targets as being two (one on each side). Conclusions When the neural circuitry subtending spatial processing is damaged, an increase in task load can lead to either a disregard or a bias in the processing of contralesional hemispace. The spatial bias subtending mislocalizations seems to index a more severe deficit than neglect, as if contralesional space would be completely erased rather than merely ignored.

Hemispatial Neglect Shows That “Before” Is “Left”

“…Patients with neglect mislabeled items belonging to the past as being “future” items both in recall and in recognitions tasks significantly more than participants without neglect did. This spatial distortion closely mirrors spatial mislocalizations in the visual space whereby contralesional targets, under demanding tasks, are reported to appear in the ipsilesional space [ 27 ].…”

Increased Cognitive Load Reveals Unilateral Neglect and Altitudinal Extinction in Chronic Stroke

“…In the dual-task context, he made 0% omissions but, on 8% of the trials, he reported having seen a stimulus in both parts of the screen, while there was a stimulus in the upper part only. This phenomenon is reminiscent of synchiria (Bonato & Cutini, 2016).…”

The Neuropsychology of Feature Binding and Conscious Perception

“…This idea is also consistent with other (above-mentioned) phenomena related to attentional deficits that may follow parietal damage: when content features are not tightly bound to the representation of their locations, because of a damage to the attentional mechanisms subtending this binding process, false conjunctions of features of different objects (e.g., in Balint patients) or allochiric misallocation of objects toward the focus of attention (e.g., in UN patients) can occur. Accordingly, an increased number of allochiric misallocations in UN patients has been observed when the availability of patients' attentional resources were further reduced by increasing the attentional load, that is, under dual-task (vs. single-task) conditions (Bonato and Cutini, 2016).…”