Adaptation to virtual prisms and its relevance for neglect rehabilitation: a single-blind dose-response study with healthy participants

Abstract

Prism adaptation (PA) has been applied with mixed success as a rehabilitation method of spatial neglect. Results from many single-case and multiple case studies as well as randomised controlled trials do not produce a clear picture of the efficacy of PA. We here tested a new method of PA, by inducing adaptation effects in the virtual reality. Healthy participants were attributed to one of four groups: no deviation, 10-, 20-, or 30-degrees rightward deviation. In contrast to classical wedge prisms, we induced the visual shift progressively. Participants performed two variants of the bisection and the landmark task to measure cognitive transfer of adaptation effects. Pointing error was directly related to the degree of optical deviation, and was greatest immediately following adaptation. Transfer was only observed in the bisection tasks, and only in the 30-degrees group. Due to the gradual induction of the spatial deviation the majority of participants were unaware of the adaptation effects. These findings show that large rightward deviation may affect sensorimotor performance in healthy participants similarly to neglect patients. Moreover, the finding that only participants adapted to 30-degrees showed biased bisection performance suggests that a critical threshold must be reached in order to induce significant visuomotor transfer.

<p>Unilateral Spatial Neglect After Stroke: Current Insights</p>

“…[94][95][96][97] A possible explanation of negative findings might be that visuomotor adaptation (ie, aftereffect) has to reach a critical threshold to affect performance in other tasks. 98 Given the high intra-and interindividual variability of individuals with USN, visuomotor adaptation induced by low power prisms (i.e., shifting the visual field of 5°, 6°or 10°)as those used in RCT studies that did not find any beneficial outcomes after PA [94][95][96][97] might be too small to produce detectable effects in all patients. The fact that the critical threshold can only be reached with prisms of high power (i.e., shifting the visual field of 10°or 12°, as those used in the above studies that found significant PA effects) might explain some negative findings.…”

“…144 A final promising protocol was tested in a single-blind dose-response study in healthy subjects, by using VR as an alternative to real prisms. 98 Authors progressively induced a displacement of the visual field following the virtual PA procedure, making difficult for the subject to become aware of the experimental manipulation. Results showed that large rightward deviations may affect sensorimotor performance in healthy participants similarly to neglect patients without generating discomfort linked to the large visual shift.…”

Immersive virtual prism adaptation therapy with depth-sensing camera: A feasibility study with functional near-infrared spectroscopy in healthy adults

“…During VPAT mode, the behavioral adaptation during pointing was observed according to the degree of virtual hand deviation (Fig 6). In recent studies with a VPAT system using HMD and a hand-held controller, healthy adults or stroke patients with USN showed clear post-VPAT adaptations in open-loop pointing (Gammeri et al 2020;Bourgeois et al 2021). The pointing errors in post-VPAT adaptation at 20° deviation was about 8° in healthy adults (Gammeri et al 2020), and that after 15° deviation VPAT was 4.4° in stroke patients with USN (Bourgeois et al 2021), similar to our study (8.48°).…”

“…Two previous studies evaluated the transfer effect of VPAT using bisection, landmark or cancellation tasks but their results were contradictory (Gammeri et al 2020;Bourgeois et al 2021). The transfer effect was observed after 30° VPAT adaptation in healthy adults (Gammeri et al 2020), but not in the cross-over study among stroke patients with USN (Bourgeois et al 2021). We think that the negative results of VPAT in the study by Bourgeois et al (Bourgeois et al 2021) with stroke patients should be cautiously interpreted.…”

“…Therefore, further clinical trials to investigate the VPAT's efficacy on USN are required. Specifically, a future trial should consider conducting multiple VPAT sessions over an extended period to prove the long-term cumulative effects (Frassinetti et al 2002;Serino et al 2007) and offer more intensity in terms of the degree of rightward deviations, considering the threshold of deviations for the immediate VPAT aftereffects (Gammeri et al 2020). In addition, a multicenter trial may have to be considered, due to the relatively small effect sizes of PA (Umeonwuka, Roos, and Ntsiea 2020) and higher severity and older ages in stroke patients with USN, preventing them to participate PA trials (Gottesman et al 2008).…”