The effect of central (macula) sparing on contralateral line bisection bias: a study with virtual hemianopia

Hemianopic patients show a contralesional bisection bias, but it is unclear whether this is a consequence of their field loss or related to extrastriate damage. One observation cited against the former is that hemianopic bisection bias does not vary with the degree of central (macular) sparing; however, it is unclear to what extent central sparing should affect this bias. Our goal was to determine the effect of central sparing on line bisection biases from field loss alone, with two approaches. First, we studied 12 healthy subjects viewing lines under conditions of virtual hemianopia, created by a gaze-contingent technique. Second, we calculated the effect predicted by a visuospatial model of the effect of central magnification on line representations in the visual system. Our results first replicated the contralateral line bisection bias with hemianopia, confirming that this can be generated by visual hemifield loss in the absence of extrastriate damage. Central sparing had only a modest effect on hemianopic bisection bias, with only slightly less bias with 10° compared to 2° of central sparing. In accordance with these empiric data, computing the center of mass for line representations in our model showed only a shallow decline in bisection bias as central sparing increased from 0 to 10°. We conclude that contralateral bisection bias only decreases slightly with central sparing, and that the absence of a statistically significant effect of central sparing in patients cannot be taken as evidence against a visual origin of contralateral hemianopic line bisection bias.     

The spatial representation of numerical and non-numerical sequences: evidence from neglect

Psychophysical and neuropsychological studies have revealed that humans represent numbers along a continuous, left-to-right oriented mental line. However, it has been recently claimed that this format of representation is not special to numbers because non-numerical sequences would be spatially coded in the same way. To test this hypothesis, the present study investigated the effects of left neglect upon the bisection of numerical and non-numerical intervals. Eight patients with left neglect performed a visual line bisection task and three mental bisection tasks with number, letter, and month intervals. The error pattern in the number bisection task, indexed by the modulating effect of interval length, mirrored that of the visual task and confirmed the left-to-right spatial orientation of the mental number line. In contrast, the bisection of non-numerical intervals showed a very different pattern. The results suggest that the spatial layout characterizing numerical representations constitutes a specific property of numbers rather than a general characteristic of ordered sequences.     

A common basis for visual and tactile exploration deficits in spatial neglect?

One of the fundamental characteristics of spatial neglect is an imbalanced visual search behaviour favouring stimuli on the right side of space while largely ignoring those on the left side. Opinions differ as to whether this reflects a general orientational bias caused by impaired supramodal body-centred reference systems, or a modality-specific search disorder. A prediction of the former model would be that exploratory activity is similarly impaired both in vision and in the absence of visual control. We addressed this hypothesis by comparing patients' visual and tactile search in the same workspace. Our results show that the centre of exploration activity in both modalities was substantially shifted towards the ipsilesional right side in the neglect group as compared to healthy and patient controls. This bias was more accentuated for visual search. We found a clear linear relationship between the visual and tactile search biases in the patient group with spatial neglect. Our finding suggests that the critical component guiding search behaviour in neglect, whether visually or tactually, is a general rightward orientation bias. In addition, we observed an increased repetition rate in both modalities which affected the whole workspace. This implies that the apparent spatial working memory deficit dissociates from the mechanisms inducing the orientation bias.     

Unconscious processing of Arabic numerals in unilateral neglect

This study explores the processing of Arabic numerals in three patients with dense left unilateral neglect. Three tasks have been used: a test of visual awareness (is the stimulus on the left, on the right or on both sides?), a number comparison task (is the number larger or smaller than 5?), a number parity judgment task (is the number odd or even?). The test of visual awareness indicated that all three patients were completely unaware of the stimuli presented in the left hemifield. Despite this, the number comparison and number parity judgment tasks clearly indicated that Arabic numerals were unconsciously processed at semantic level (i.e. quantity). These results show that patients with left unilateral neglect can still semantically process Arabic numerals unconsciously.     

Visuomotor functions of the posterior parietal cortex

In this special issue of Neuropsychologia leading experts in the field discuss controversies and advances in the role of the posterior parietal cortex (PPC) in visuomotor control. The papers are wide-ranging in their scope, covering monkey physiology and anatomy, functional imaging in humans and monkeys as well as transcranial magnetic stimulation and lesion studies in humans. The collection provides an important overview of the current state-of the-art in this area of research, including discussions on homologies between monkey and human parietal regions, the role of co-ordinate transformations and intermediate representations from vision to action, and reviews of controversial hot topics in this field.     

Pseudoneglect for mental alphabet lines is affected by prismatic adaptation

While patients with right parietal damage and spatial neglect bisect lines to the right, the general population bisects lines to the left; a phenomenon known as pseudoneglect. The leftward bias also occurs for mental representations, such as number and alphabet lines. Prismatic adaptation can have a dramatic effect on attentional bias and corrects neglect and pseudoneglect for physical and mental number lines. This study examined whether prismatic adaptation can correct leftward bisection biases for alphabet lines, which may have a different spatial arrangement compared to number lines. In pre-adaptation testing, students (n = 42) were shown letter trigrams (e.g. C H P) and judged whether the alphabetical distance before or after the inner-letter was larger. Participants were then split into three groups and were adapted to left-shifting, control or right-shifting prims. After adaptation, the mental alphabet bisection task was re-administered. The length of left side of the alphabet lines was overestimated by all three groups in the pre-adaptation phase. Right-shifting prisms and control spectacles had no effect on the leftward bias whereas exposure to left-shifting prisms corrected the bias. The results replicate an effect observed for mental number lines and demonstrate that low-level sensory-motor shifts can correct attentional biases associated with high-level representations, such as letters.     

The prevalence of non-accidental trauma among children with polytrauma: A nationwide level-I trauma centre study

ObjectiveWe aimed to investigate the prevalence and characteristics of non-accidental trauma (NAT) in children with polytrauma treated at level-I trauma centres (TC).Summary of backgroundData 6–10% Of children who present at the emergency department with injuries, sustain polytrauma. Polytrauma may result from either accidental (AT) or NAT, i.e. inflicted or neglect. The prevalence of NAT among children with polytrauma is currently unclear.MethodsThis is a retrospective study that included children (0–18 years) with an Injury Severity Score >15, who presented at one of the 11 Level-I trauma centers (TC) in the Netherlands between January 1, 2010 and January 1, 2016. Outcomes were classified based on the conclusions of the Child Abuse and Neglect-team. Cases in which conclusions were unavailable and there was no clear accidental cause of injuries were reviewed by an expert panel.ResultsThe study included 1623 children, 1452 (89%) were classified as AT, 171 (11%) as NAT; 39 (2,4%) inflicted and 132 (8,1%) neglect. Of pre-school aged children (<5 years) 41% sustained NAT (OR26.73, 95%CI 17.70–40.35), 35/342 (10%) inflicted and 104/342 (31%) neglect. Admission due to ‘cardiopulmonary arrest’ was the result of inflicted trauma (30% vs 0%,p < 0.001). NAT had a higher mortality rate (16% vs 10%, p = 0.006). Indicators of NAT were: (near-)drowning (OR10.74, 95%CI 5.94–19.41), burn (OR8.62, 95%CI 4.08–18.19) and fall from height (OR2.18, 95%CI 1.56–3.02).ConclusionsNAT was the cause of polytrauma in 11% of children in our nationwide level-I TC study; 41% of these polytrauma were the result of NAT experienced by preschool-aged children. Our data show the importance of awareness for NAT.     

Lasting improvements in left spatial neglect following a protocol combining neck-muscle vibration and voluntary arm movements: a case-study

Purpose: Beyond promising experimental results of sensory passive stimulations in spatial cognition disorders, some questions still remain regarding interests of these stimulations during the daily activities in neglect. The aim of this case-study was to evaluate the effects of a protocol combining left neck-muscle vibration with daily simple movements, like arm pointing movements, on perceptivo-locomotor deficits in a left spatial neglect patient.

Materials and methods: Two neuropsychological tests, one subjective straight-ahead pointing (SSA) test and one wheelchair navigation test were carried out before the combination protocol, immediately after, 1?h later, and 24?h later.

Results: The results showed a reduction of neglect spatial bias following the protocol lasted at least 24?h in all the tests (except for the SSA test due to the unavailability of the pointing device).

Conclusions: The range of improvements in the symptoms of spatial neglect suggests that this therapeutic intervention based on the combining neck-muscle vibration to voluntary arm movements could be a useful treatment for this condition. One of future investigation axes should be the development of a vibratory tool in order to facilitate the combining this proprioceptive stimulation to daily activities.

• Implications for rehabilitation

• Spatial neglect is a perplexing neuropsychological syndrome, affecting different domains of spatial cognition and impacting also the functional domain.

• The treatments based on neck-muscle vibration are simple to use, non-invasive and requires none active participation of patient.

• A therapeutic intervention based on the combining left neck-muscle vibration and voluntary arm movements in a left-spatial-neglect show a lasting reduction of symptoms especially in daily activities.

• The combination of treatments based on the Bottom–Up approach opens innovative perspectives in rehabilitation.

     

Sensory and response contributions to visual awareness in extinction

Brain-damaged patients may extinguish contralesional stimuli when ipsilesional stimuli are presented simultaneously. Most theories of extinction postulate that stimuli compete for pathologically limited attentional resources with a bias to process ipsilesional over contralesional stimuli. Implicit in this view is the idea that responses follow the outcome of an earlier competition between inputs. In the current study of two patients, we used signal detection analyses to test the hypothesis that response criteria and response modalities also contribute to visual awareness. We found that identification was more sensitive than detection in uncovering deficits of contralesional awareness. Extinction was worse with bilateral stimuli when the ipsilesional stimulus was identical or similar to the target than when it was dissimilar. This diminished awareness was more likely to reflect a shift towards more conservative responses rather than diminished discrimination of contralesional stimuli. By contrast, one patient was better able to discriminate contralesional stimuli when using his contralesional limb to indicate awareness of targets than when using his ipsilesional limb. These data indicate that the nature of stimuli can modulate response criteria and the motor response can affect the sensory discriminability. Sensory discrimination and response output are not organized in a simple serial manner. Rather, input and output parameters interact in complicated ways to produce visual awareness. Visual awareness itself appears to be the outcome of two bottlenecks in processing, one having to do with sensory processing that may be covert and the other having to do with decision making, which by definition is overt. Finally, we advocate the use of signal detection analyses in studies of extinction, a method that has been surprisingly neglected in this line of research.