Influences of visual pitch and visual yaw on visually perceived eye level (VPEL) and straight ahead (VPSA) for erect and rolled-to-horizontal observers

Abstract

Localization within the space in front of an observer can be specified along two orthogonal physical dimensions: elevation ('up', 'down') and horizontal ('left','right'). For the erect observer, these correspond to egocentric dimensions along the long and short axes of the body, respectively. However, when subjects are rolled-to-horizontal (lying on their sides), the correspondence between the physical and egocentric dimensions is reversed. Employing egocentric coordinates, localization can be referred to a central perceptual point-visually perceived eye level (VPEL) along the long axis of the body, and visually perceived straight ahead (VPSA) along the short axis of the body. In the present experiment, measurements of VPEL and of VPSA were made on each of eight subjects who were either erect or rolled-to-horizontal while monocularly viewing a long 2-line stimulus (two parallel, 64 degrees -long lines separated by 50 degrees ) in otherwise complete darkness that was centered on the eye of the observer and was tilted out of the frontoparallel plane by a variable amount and direction (from -30 degrees to +30 degrees in 10 degrees steps). The stimulus tilt was either around an axis through the center of the two eyes (pitch; VPEL was measured) or around the long axis of the body that passed through the center of the viewing eye (yaw; VPSA was measured). Large variations in the localization settings were measured that were systematic with stimulus tilt. The slopes of the functions plouing the deviations from veridicality against the orientation of the 2-line stimulus ('induction functions') were larger for the rolled-to-horizontal observer than for the erect observer for both VPEL and VPSA, and for a given body orientation were larger for the VPEL discrimination than for the VPSA discrimination; the influences of body orientation in physical space and the direction of the discrimination relative to the body were lineraly additive. Both the y-intercepts of the induction functions and the central perceptual point measured in complete darkness were lower when the norm setting by the subject was along the vertical than when it was along the horizontal; this held for both the VPEL and VPSA discriminations. The systematic effects of body orientation on the slopes and of line orientation on the y-intercepts and dark values result from an effect of gravity on the settings and fit well to a general principle: any departure from erect posture increases the induction effects of the visual stimulus. The effect of gravity is consistent with the effect of gravity in previous work in high-g environments with the VPEL discrimination.

Influence of gaze elevation on estimating the possibility of passing under high obstacles during body tilt

“…Numerous authors have stressed the importance of eye level in height and distance judgments (Li et al 2001;Matin and Li 1995;Ooi et al 2001). Specifically, eye level is commonly considered as a central reference in egocentric (Matin and Li 1995) and geocentric spatial localization in darkness (Bringoux et al 2004(Bringoux et al , 2008Stoper and Cohen 1989).…”

The Rod-and-Frame Effect: The Whole is Less than the Sum of its Parts

“…That this was essentially Witkin's view at the time he died in 1979 was noted by his close colleague in a symposium to Witkin's memory (Goodenough 1986). This latter view, in which the rod-and-frame illusion is treated as a set of phenomena whose determinants lie largely within more primitive neurophysiologically based special systems regulating space perception, has become the common approach to studying a number of large-field spatial illusions in several different dimensions since the 1970s (Dichgans et al 1972;Dichgans and Brandt 1974;Mittelstaedt 1986Mittelstaedt , 1988Matin and Fox 1989;Matin and Li 1992, 1994b, 1995, 1999Hudson et al 2000, in press;Li et al 2001). The major basis for the large individual differences in dependence on the visual field can be interpreted as differences in the extent to which the influences are weighted toward vision or toward a body-referenced mechanism (1) separately from theories concerning higher-level cognitive/personality traits.…”

Short-lived effects of a visual inducer during egocentric space perception and manual behavior

“…Moreover, the small average negative bias (-2.9°w ith the erect inducer) also appeared in the data for the individual subjects. See Li, Dallal, and Matin (2001, pp. 2888-2889 for a discussion of the theoretical significance of the bias in VPEL functions and for references related to this issue.…”

“…The effects are very large and vary linearly with the pitch of the inducer over a wide range. Furthermore, they are not limited to a target that appears to be at eye level-targets above and below VPEL undergo a similar translation, as if the VPEL established a zero-point on a subjective elevation dimension (Li, Dallal, & Matin, 2001;Li & L. Matin, 2005;Robison, Li, & Matin, 1995).…”