Academic journal article Attention, Perception and Psychophysics

The Effects of Luminance, Size, and Duration of a Visual Line on Apparent Vertical While the Head Is Being Inclined in Roll

Academic journal article Attention, Perception and Psychophysics

The Effects of Luminance, Size, and Duration of a Visual Line on Apparent Vertical While the Head Is Being Inclined in Roll

Article excerpt

Published online: 28 October 2014

(Q> The Psychonomic Society, Inc. 2014

Abstract We determined orientation of a line that is seen to be vertical (i.e., apparent vertical) while the head is inclined with the trunk upright. In this condition, it has been documented that apparent vertical is independent of head orientation (i.e., orientation constancy) or is in a direction opposite to the head inclination (i.e., the Müller effect). In this study, we have focused not only on the effect of head inclination but also on visual parameters of the line that was used to indicate apparent vertical. As the visual parameters, size (5.5° and 22° in visual angle), duration (0.1 s, 3 s, and no time limit), and luminance (0.026, 0.003, and 0.001 cd/m^sup 2^ against total darkness) were varied with the head being inclined within ±30°. The main findings were: 1) the Müller effect was at best 2°, but the head inclination was judged to be much larger than it was; 2) the correlation between apparent vertical and the judgmental error of head inclination was significant but was not very high (r = -0.20); 3) the line of short duration or of low luminance facilitated the Müller effect; and 4) the magnitude of the Müller effect was large when the head was inclined to the right rather than to the left. These findings were compared with the predictions from the theory of allowing for apparent head position, the theory of ocular countertorsion, and the sensory-tonic field theory. Many aspects of the results were consistent with the predictions from the sensory-tonic field theory.

Keywords Spatial Vision . Multisensory Processing . Kinesthesis

Apparent vertical or horizontal is defined as the orientation of a line that is seen to be vertical or horizontal. It provides the frame of reference in space perception, because orientation of a visual line in the frontal plane is usually judged with respect to apparent vertical or horizontal. In this paper, we address apparent vertical. It seems that apparent vertical is determined by a complex process of head/trunk inclination that accompanies changes in vestibular and somesthetic inputs (Day & Wade, 1969; Ebenholtz, 2001; Lackner & DiZio, 2005; Howard, 1982, 1986 for review) and other sensory factors that include visual, auditory, and tactile stimulation (Wapner & Werner, 1957; Werner & Chandlar, 1951; Werner & Wapner, 1952).

Apparent vertical often was determined by adjusting orientation of a luminous line in otherwise total darkness (De Vrijer, Medendorp, & van Gisbergen, 2009; Mast, 2000; van Beuzekom, Medendorp, & van Gisbergen, 2001; Wade & Curthoys, 1997; Yardley, 1990) or in visually informative conditions (Dyde, Jenkin, & Harris, 2006). In other studies, apparent vertical was determined by haptically adjusting orientation of a rod (Bortolami, Pierobon, DiZio, & Lackner, 2006; Bauermeister, 1964; Wade & Curthoys, 1997).

In both visual and haptic adjustments, it has been shown that apparent vertical depends on whole body (or the head-trunk ensemble) inclination: for a small inclination up to 10°, the apparent vertical approximated the gravitational vertical (i.e., constancy; Tamutzer, Bockisch, & Straumann, 2010 for a recent study); for a moderate inclination between 20° and 60°, it was in a direction opposite to the body inclination (i.e., the Müller effect, 1916; Wade & Curthoys, 1997 for a recent study); and for a large inclination between 60° and 90°, it was in the same direction as the body inclination (i.e., the Aubert effect, 1861; van Beuzekom et al., 2001 and Trousselard et al., 2003 for recent studies). It also was reported that for the inclination of 120-130°, there was a sudden alternation between the Müller and the Aubert effects (Kaptein & van Gisbergen, 2004).

When the head and the trunk differ in orientation, the apparent vertical differs from the apparent vertical obtained for the aligned head-trunk combination. …

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