Different strategies in pointing tasks and their impact on clinical bedside tests of spatial orientation

Subjective spatial orientation discomfort is associated with decreased real-world spatial performance and lower cognitive function

Background

Spatial memory and orientation deficits often precede cognitive impairment in incipient dementia, e.g., Alzheimer's disease. Therefore, early diagnosis of spatial impairment may be crucial to the initiation of an adequate therapeutic intervention. Subjective tests, such as spatial anxiety and spatial discomfort questionnaires, and objective tests in the form of quantitative measures of orientation, are available. In these tests, vestibular hypofunction has often been neglected as a potential confounder. The major research question in this study was how self-assessed questionnaires correlate with the data from objective measures in participants with proven normal vestibular function.

Methods

A heterogeneous group of 135 participants (72 females, 63 males, mean age 62.75 ± 14.46 years) from a tertiary center for vertigo and balance disorders consisting of two cohorts, with (n = 49) and without (n = 86) cognitive deficits in a screening test (MoCA), was examined (a) with a newly introduced inventory for subjective spatial discomfort (Extended Inventory for Spatial Orientation Discomfort, EISOD), (b) a well-established questionnaire for subjective spatial skills (Santa Barbara Sense of Direction Scale, SBSODS), and (c) the objective three-dimensional real-world pointing task (3D-RWPT) before and after horizontal body rotations. In all patients, acute central or peripheral vestibular deficits were ruled out by neuro-orthoptics, bithermal water calorics and video head impulse testing.

Results

Self-assessed spatial orientation discomfort (EISOD) correlated with the amount of spatial impairment in the 3D-RWPT for both cohorts. The cognitively impaired patients showed significantly higher levels of spatial discomfort (i.e., lower scores; Welch's t-test t-2.58, p < 0.01, Cohen's d - 0.46), and higher angular deviations in the (cognitively demanding) transformation paradigm of the 3D-RWPT (t 2.37, p 0.02, Cohen's d 0.44). They preferred retinotopic/egocentric spatial encoding strategies in the pointing task (Welch's t-test t-2.61, p < 0.01, Cohen's d - 0.47). In contrast, the self-report of spatial abilities (SBSODS) yielded no significant group differences (t - 1.66, p 0.10) and was not reliably associated with objective accuracy in the pointing task.

Conclusion

In patients without vestibular deficits, subjective spatial discomfort (EISOD) correlated with the accuracy in an objective 3D-pointing task for both cohorts, and higher discomfort was associated with more severe cognitive impairment. EISOD-scores showed higher correlation indices than a self-report of spatial skills using the SBSODS. When investigating spatial abilities in patients with suspected cognitive impairment, it appears reasonable that both subjective spatial discomfort, subjective spatial abilities, and objective spatial measures should be combined. Future research in patients with vestibular dysfunction is needed to understand the role of vestibular deficits for the development of spatial orientation discomfort.

A clinical 3D pointing test differentiates spatial memory deficits in dementia and bilateral vestibular failure

BACKGROUND

Deficits in spatial memory, orientation, and navigation are often neglected early signs of cognitive impairment or loss of vestibular function. Real-world navigation tests require complex setups. In contrast, simple pointing at targets in a three-dimensional environment is a basic sensorimotor ability which provides an alternative measure of spatial orientation and memory at bedside. The aim of this study was to test the reliability of a previously established 3D-Real-World Pointing Test (3D-RWPT) in patients with cognitive impairment due to different neurodegenerative disorders, bilateral vestibulopathy, or a combination of both compared to healthy participants.

METHODS

The 3D-RWPT was performed using a static array of targets in front of the seated participant before and, as a transformation task, after a 90-degree body rotation around the yaw-axis. Three groups of patients were enrolled: (1) chronic bilateral vestibulopathy (BVP) with normal cognition (n = 32), (2) cognitive impairment with normal vestibular function (n = 28), and (3) combined BVP and cognitive impairment (n = 9). The control group consisted of age-matched participants (HP) without cognitive and vestibular deficits (n = 67). Analyses focused on paradigm-specific mean angular deviation of pointing in the azimuth (horizontal) and polar (vertical) spatial planes, of the preferred pointing strategy (egocentric or allocentric), and the resulting shape configuration of the pointing array relative to the stimulus array. Statistical analysis was performed using age-corrected ANCOVA-testing with Bonferroni correction and correlation analysis using Spearman's rho.

RESULTS

Patients with cognitive impairment employed more egocentric pointing strategies while patients with BVP but normal cognition and HP used more world-based solutions (pBonf 5.78 × 10-3**). Differences in pointing accuracy were only found in the azimuth plane, unveiling unique patterns where patients with cognitive impairment showed decreased accuracy in the transformation tasks of the 3D-RWPT (pBonf < 0.001***) while patients with BVP struggled in the post-rotation tasks (pBonf < 0.001***). Overall azimuth pointing performance was still adequate in some patients with BVP but significantly decreased when combined with a cognitive deficit.

CONCLUSION

The 3D-RWPT provides a simple and fast measure of spatial orientation and memory. Cognitive impairment often led to a shift from world-based allocentric pointing strategy to an egocentric performance with less azimuth accuracy compared to age-matched controls. This supports the view that cognitive deficits hinder the mental buildup of the stimulus pattern represented as a geometrical form. Vestibular hypofunction negatively affected spatial memory and pointing performance in the azimuth plane. The most severe spatial impairments (angular deviation, figure frame configuration) were found in patients with combined cognitive and vestibular deficits.

Vestibular contribution to spatial orientation and navigation

PURPOSE OF REVIEW

The vestibular system provides three-dimensional idiothetic cues for updating of one's position in space during head and body movement. Ascending vestibular signals reach entorhinal and hippocampal networks via head-direction pathways, where they converge with multisensory information to tune the place and grid cell code.

RECENT FINDINGS

Animal models have provided insight to neurobiological consequences of vestibular lesions for cerebral networks controlling spatial cognition. Multimodal cerebral imaging combined with behavioural testing of spatial orientation and navigation performance as well as strategy in the last years helped to decipher vestibular-cognitive interactions also in humans.

SUMMARY

This review will update the current knowledge on the anatomical and cellular basis of vestibular contributions to spatial orientation and navigation from a translational perspective (animal and human studies), delineate the behavioural and functional consequences of different vestibular pathologies on these cognitive domains, and will lastly speculate on a potential role of vestibular dysfunction for cognitive aging and impeding cognitive impairment in analogy to the well known effects of hearing loss.

Measuring visually guided motor performance in ultra low vision using virtual reality

Introduction

Ultra low vision (ULV) refers to profound visual impairment where an individual cannot read even the top line of letters on an ETDRS chart from a distance of 0.5 m. There are limited tools available to assess visual ability in ULV. The aim of this study was to develop and calibrate a new performance test, Wilmer VRH, to assess hand-eye coordination in individuals with ULV.

Methods

A set of 55 activities was developed for presentation in a virtual reality (VR) headset. Activities were grouped into 2-step and 5-step items. Participants performed a range of tasks involving reaching and grasping, stacking, sorting, pointing, throwing, and cutting. Data were collected from 20 healthy volunteers under normal vision (NV) and simulated ULV (sULV) conditions, and from 33 participants with ULV. Data were analyzed using the method of successive dichotomizations (MSD), a polytomous Rasch model, to estimate item (difficulty) and person (ability) measures. MSD was applied separately to 2-step and 5-step performance data, then merged to a single equal interval scale.

Results

The mean ± SD of completion rates were 98.6 ± 1.8%, 78.2 ± 12.5% and 61.1 ± 34.2% for NV, sULV and ULV, respectively. Item measures ranged from -1.09 to 5.7 logits and - 4.3 to 4.08 logits and person measures ranged from -0.03 to 4.2 logits and -3.5 to 5.2 logits in sULV and ULV groups, respectively. Ninety percent of item infits were within the desired range of [0.5,1.5], and 97% of person infits were within that range. Together with item and person reliabilities of 0.94 and 0.91 respectively, this demonstrates unidimensionality of Wilmer VRH. A Person Item map showed that the items were well-targeted to the sample of individuals with ULV in the study.

Discussion

We present the development of a calibrated set of activities in VR that can be used to assess hand-eye coordination in individuals with ULV. This helps bridge a gap in the field by providing a validated outcome measure that can be used in vision restoration trials that recruit people with ULV, and to assess rehabilitation outcomes in people with ULV.

Shape configuration of mental targets representation as a holistic measure in a 3D real world pointing test for spatial orientation

Deficits in spatial memory are often early signs of neurological disorders. Here, we analyzed the geometrical shape configuration of 2D-projections of pointing performances to a memorized array of spatially distributed targets in order to assess the feasibility of this new holistic analysis method. The influence of gender differences and cognitive impairment was taken into account in this methodological study. 56 right-handed healthy participants (28 female, mean age 48.89 ± 19.35 years) and 22 right-handed patients with heterogeneous cognitive impairment (12 female, mean age 71.73 ± 7.41 years) underwent a previously validated 3D-real-world pointing test (3D-RWPT). Participants were shown a 9-dot target matrix and afterwards asked to point towards each target in randomized order with closed eyes in different body positions relative to the matrix. Two-dimensional projections of these pointing vectors (i.e., the shapes resulting from the individual dots) were then quantified using morphological analyses. Shape configurations in healthy volunteers largely reflected the real-world target pattern with gender-dependent differences (ANCOVA area males vs. females F(1,73) = 9.00, p 3.69 × 10-3, partial η2 = 0.10, post-hoc difference = 38,350.43, pbonf=3.69 × 10-3**, Cohen's d 0.76, t 3.00). Patients with cognitive impairment showed distorted rectangularity with more large-scale errors, resulting in decreased overall average diameters and solidity (ANCOVA diameter normal cognition/cognitive impairment F(1,71) = 9.30, p 3.22 × 10-3, partial η2 = 0.09, post-hoc difference = 31.22, pbonf=3.19 × 10-3**, Cohen's d 0.92, t 3.05; solidity normal cognition/cognitive impairment F(1,71) = 7.79, p 6.75 × 10-3, partial η2 = 0.08, post-hoc difference = 0.07, pbonf=6.76 × 10-3** Cohen's d 0.84, t 2.79). Shape configuration analysis of the 3D-RWPT target array appears to be a suitable holistic measure of spatial performance in a pointing task. The results of this methodological investigation support further testing in a clinical study for differential diagnosis of disorders with spatial memory deficits.

Different approaches to test orientation of self in space: comparison of a 2D pen-and-paper test and a 3D real-world pointing task

Spatial orientation is based on a complex cortical network with input from multiple sensory systems. It is affected by training, sex and age as well as cultural and psychological factors, resulting in different individual skill levels in healthy subjects. Various neurological disorders can lead to different patterns or specific deficits of spatial orientation and navigation. Accordingly, numerous tests have been proposed to assess these abilities. Here, we compare the results of (1) a validated questionnaire-based self-estimate of orientation/navigation ability (Santa Barbara Sense of Direction Scale, SBSODS) and (2) a validated pen-and-paper two-dimensional perspective test (Perspective Taking Spatial Orientation Test, SOT) with (3) a newly developed test of finger-arm pointing performance in a 3D real-world (3D-RWPT) paradigm using a recently established pointing device. A heterogeneous group of 121 participants (mean age 56.5 ± 17.7 years, 52 females), including 16 healthy volunteers and 105 patients with different vestibular, ocular motor and degenerative brain disorders, was included in this study. A high correlation was found between 2D perspective task and 3D pointing along the horizontal (azimuth) but not along the vertical (polar) plane. Self-estimated navigation ability (SBSODS) could not reliably predict actual performance in either 2D- or 3D-tests. Clinical assessment of spatial orientation and memory should therefore include measurements of actual performance, based on a 2D pen-and-paper test or a 3D pointing task, rather than memory-based questionnaires, since solely relying on the patient's history of self-estimated navigation ability results in misjudgments. The 3D finger-arm pointing test (3D-RWPT) reveals additional information on vertical (polar) spatial performance which goes undetected in conventional 2D pen-and-paper tests. Diseases or age-specific changes of spatial orientation in the vertical plane should not be clinically neglected. The major aim of this pilot study was to compare the practicability and capability of the three tests but not yet to prove their use for differential diagnosis. The next step will be to establish a suitable clinical bedside test for spatial memory and orientation.