Apparent size as a function of vertical gaze direction: New tests of an old hypothesis.

Abstract

The hypothesis was tested that the decline of apparent size with elevated gaze results from a latent tendency of the eyes to diverge and thus increased vergence effort. Through the use of a method of category estimation, the decline of apparent size on elevation or depression of gaze was found not to be different between subjects with larger or smaller changes of dark vergence and thus vergence effort. In a 2nd experiment, vergence effort was varied by varying gaze elevation and the angle of convergence. With vergence effort constant, apparent size was dependent on the angle of convergence rather than being constant. It is concluded that apparent size does not depend on vergence effort and that the effect of gaze elevation on apparent size cannot be attributed to its concomitant effect on dark vergence.

Using eye height in different postures to scale the heights of objects.

“…This is known as the “angle of regard hypothesis.” In the present experiment, just such a visual angle was required for participants to see the tops of the targets while lying prone on the floor. However, there is no clear empirical evidence to support such a claim (e.g., Heuer, Wischmeyer, Brüwer, & Römer, 1991; Plug & Ross, 1989).…”

The moon illusion: Kaufman and Rock's (1962) apparent‐distance theory reconsidered1

“…This apparatus, however, was not necessarily perfect. For one thing, to view the artificial (virtual) moon superimposed on the half‐silvered mirror (5 cm × 5 cm), their participants must have been very restricted (see also Footnote 7). Even very small movements of the eye, head or body would have slipped the artificial moon away from the mirror, so it was necessary for the participant to fixate on the image of the moon without any eye‐head‐body movements.…”

“…13 13 Vergence effort (muscular tension in the two coordinated eyes) has often been thought to be responsible for the effect of eye elevation on apparent size: more than 100 years ago, Zoth (1899) had taken vergence effort as a probable cause for the moon illusion. However, Heuer, Wischmeyer, Brüwer, and Römer (1991) showed that the difference in apparent size might not result from vergence effort, but dependent partly on vergence itself. …”

A curious illusion suggests complex cue interactions in distance perception.

“…von Hofsten, 1976). Alteration of vergence-specified distance may be achieved by introducing a bias to the vergence system (changing the open loop vergence bias, or heterophoria ) either by adapting to the presence of a prism over one eye (Owens & Leibowitz, 1980) or by fixating a close target for an extended period (Heuer, Wischmeyer, Bruwer, & Romer, 1991; Shebilske, Karmiohl, & Proffitt, 1983). It has been observed that inducing convergent biases results in the expected overestimation of distance (Ebenholtz & Wolfson, 1975; Heuer et al, 1991; Owens & Leibowitz, 1980; Shebilske et al, 1983).…”

“…Alteration of vergence-specified distance may be achieved by introducing a bias to the vergence system (changing the open loop vergence bias, or heterophoria ) either by adapting to the presence of a prism over one eye (Owens & Leibowitz, 1980) or by fixating a close target for an extended period (Heuer, Wischmeyer, Bruwer, & Romer, 1991; Shebilske, Karmiohl, & Proffitt, 1983). It has been observed that inducing convergent biases results in the expected overestimation of distance (Ebenholtz & Wolfson, 1975; Heuer et al, 1991; Owens & Leibowitz, 1980; Shebilske et al, 1983). There are also several reports of distance underestimation following prolonged fixation of more distant stimuli, and these results have been attributed to the induction of divergent bias (Ebenholtz & Wolfson, 1975; Heuer & Luschow, 1983; Paap & Ebenholtz, 1976).…”