Effect of prism adaptation on the perceived visual vertical

The purpose of this study is to explore how the human brain code for spatial representation and whether spatial coding in different dimensions share common processes. To this end, we will investigate within the same participants whether prism adaptation (Prablanc et al., 2020; Rossetti et al., 1998) can shift the orientation of the perceived visual vertical (VV) and straight-ahead (SA) in a congruent, co-dependent, fashion. During prism adaptation, participants will be asked to perform a dynamic pointing task while bearing glasses shifting the visual field by 10° rightward or leftward. Each participant will undergo the left prisms and right prisms conditions across two sessions separated by at least one week. VV and SA will be measured before and after prism adaptation. In a first recent pre-registered study (https://osf.io/dfe7t), we found the VV shifts (posttest – pretest) to differ significantly (p = .025) between the left and right prisms conditions. Nevertheless, in this first study the left and right prisms conditions were performed by two independent groups, resulting in weak statistical power (around 50%). To be more confident that prisms can bias verticality perception or not, we will therefore try to replicate this effect with a well-powered (80%) within-subjects design.