The role of the pitched-up orientation of the otoliths in two recent models of the subjective vertical

Publisher Website
Google Scholar
Abstract
Two recent models of the subjective vertical (SV), proposed by Dai, Curthoys and Halmagyi (1989; abbr. DCH-model) and by Mittelstaedt (1983a, b, 1988; abbr. M-model), respectively, are analyzed, experimentally tested and evaluated with regard to the role they attribute to the consequences of the pitchedup orientation of the labyrinth in the human skull. In the DCH-model the response to the resulting pitch shear is, after subtraction from a constant reference and normalization, multiplied with the response to roll shear and thence leads to the well-known Müller- and Aubert-deviations from veridicality. In the M-model the pitched-up orientation is accounted for by a shortcut type of coordinate transformation: subtraction of the saccular afference from the utricular response to pitch yields the head-fixedX-(pitch)component, whereas their addition yields the head-fixedZ-component. The SV will be veridical in a normal range of head positions if the amplitude of the saccular response is related to the utricular one as the sine is to the cosine of the pitched-up angle (≈ 30°). But then, typical deviations must result in other specifiable positions. The DCH- and the M-model are experimentally tested in positions where they predict SV-deviations of opposite sign. The results in 5 partly naive partly well-versed probands are highly significantly different from the DCH-model predictions whereas well compatible with those of the M-model. The implications for the models under scrutiny are discussed as well as for the global modelling of systems when essential internal constituents are unknown or inaccessible.