The subjective vertical as a function of visual and extraretinal cues

Abstract

This contribution tries to generalize a theory about the effect of the gravity and idiotropic vectors on the subjective vertical (SV) by encompassing the influence of ‘verticalizing’ visual patterns. Such patterns are first experimentally shown to form a resultant with, rather than to suppress, the gravito-idiotropic vector. By varying the position of the visual panorama, its effect on this resultant turns out to be determined by sine functions of the angle between the SV and the upright axis of the panorama, and of the angle's multiples (named ‘SV-function’). The peculiar features of the visual influence, and its seemingly incompatible effects in earlier experiments on tilt illusions are shown to result from qualitative and quantitative properties of the SV-function. The underlying information processing structure — after experimental falsification of two feedforward variants — is envisaged to contain a central nervous component generator, which is controlled by internal feedback of its own output, after the latter is cross-multiplied with circular Fourier components selected from a central nervous representation of the retinal pattern. Lastly, a weighting procedure is suggested which may extract the required even number circular Fourier components from arrays of cortical neurons of known properties.