The subjective visual vertical and the perceptual upright

Abstract

The direction of 'up' has traditionally been measured by setting a line (luminous if necessary) to the apparent vertical, a direction known as the 'subjective visual vertical' (SVV); however for optimum performance in visual skills including reading and facial recognition, an object must to be seen the 'right way up'--a separate direction which we have called the 'perceptual upright' (PU). In order to measure the PU, we exploited the fact that some symbols rely upon their orientation for recognition. Observers indicated whether the symbol 'horizontal P' presented in various orientations was identified as either the letter 'p' or the letter 'd'. The average of the transitions between 'p-to-d' and 'd-to-p' interpretations was taken as the PU. We have labelled this new experimental technique the Oriented CHAracter Recognition Test (OCHART). The SVV was measured by estimating whether a line was rotated clockwise or counter-clockwise relative to gravity. We measured the PU and SVV while manipulating the orientation of the visual background in different observer postures: upright, right side down and (for the PU) supine. When the body, gravity and the visual background were aligned, the SVV and the PU were similar, but as the background orientation and observer posture orientations diverged, the two measures varied markedly. The SVV was closely aligned with the direction of gravity whereas the PU was closely aligned with the body axis. Both probes showed influences of all three cues (body orientation, vision and gravity) and these influences could be predicted from a weighted vectorial sum of the directions indicated by these cues. For the SVV, the ratio was 0.2:0.1:1.0 for the body, visual and gravity cues, respectively. For the PU, the ratio was 2.6:1.2:1.0. In the case of the PU, these same weighting values were also predicted by a measure of the reliability of each cue; however, reliability did not predict the weightings for the SVV. This is the first time that maximum likelihood estimation has been demonstrated in combining information between different reference frames. The OCHART technique provides a new, simple and readily applicable method for investigating the PU which complements the SVV. Our findings suggest that OCHART is particularly suitable for investigating the functioning of visual and non-visual systems and their contributions to the perceived upright of novel environments such as high- and low-g environments, and in patient and ageing populations, as well as for normal observers.

When Up Is Down in 0g: How Gravity Sensing Affects the Timing of Interceptive Actions

“…The integration of visual, tactile, and proprioceptive signals, in addition to other graviceptors, would explain why subjects may react to targets moving off the gravitational axis (Miller et al, 2008;Moscatelli and Lacquaniti, 2011) or in weightlessness (McIntyre et al, 2001) as if the targets were moving downward, as noted above. Idiosyncratic differences in the weighting of different sensory modalities could also explain why some subjects did not show a timing reversal in weightlessness, in much the same way that individuals depend differently on visual, graviceptor and idiotropic cues to define the perceived vertical (Dyde et al, 2006) and that not all subjects experience conscious illusions of being turned upside-down in weightlessness (Simons and Gardner, 1963;Lackner, 1992). In fact, according to one theory, vestibular signals are ambiguous anyway, such that additional sensory cues are required to determine up and down even in a normal Earth environment (Bortolami et al, 2006).…”

Necessity is the Mother of Invention: Reconstructing Missing Sensory Information in Multiple, Concurrent Reference Frames for Eye–Hand Coordination

“…Kinesthetic representations are presumed to be referenced to egocentric proprioceptors and/or gravity (Soechting and Ross, 1984;Darling and Gilchrist, 1991) and would therefore be immune to the artificial deviation of the visual surround that we imposed during the head movement. The visual representation however, would be referenced both to the visual surround, to gravity, and to the head/ retinal axis Witkin and Asch, 1948;Luyat and Gentaz, 2002;Jenkin et al, 2003Jenkin et al, , 2005Dyde et al, 2006;McIntyre and Lipshits, 2008). Artificial tilt of the visual surround would cause the visual representation to deviate with respect to the physical vertical, although not necessarily by 100%.…”

Verticality Perception During Off-Vertical Axis Rotation

“…1A, which extends the canal-otolith interaction model with a stage that can explain the static A-effects in verticality perception. Inspired by several studies (Dyde et al 2006;Groen et al 2002;Mittelstaedt 1983;Zupan and Merfeld 2005;Zupan et al 2002), we modeled the subjective vertical as a weighted vector sum of the estimated direction of gravity and the direction of the long-body axis (g ϭ ĝ ϩ w⅐h; see Fig. 1B).…”