Closed-loop and open-loop accommodative vergence eye movements.

We examined accommodative vergence eye movements under conditions in which feedback about retinal-image slip was and was not present (i.e. closed-loop and open-loop conditions). We found that (a) in both conditions the two eyes started to move at the same time; (b) in the open-loop condition, vergence continued in both eyes; and (c) in the closed-loop condition, vergence continued in the occluded eye only, and the magnitude and velocity exceeded that of the occluded eye in the open-loop condition by a factor of two.

Wondering about the wandering cyclopean eye.

Arguments against recent claims (Erkelens, Muijs & van Ee (1996). Vision Research, 36, 2141-2147; Mansfield & Legge (1996). Vision Research, 36, 27-41. (1997), Vision Research, 37, 1610-1613) that the position of the cyclopean eye is stimulus specific are presented. Critical to these arguments are the differences between relative and absolute visual direction tasks (Howard (1982). Human visual orientation. Wiley, New York; Ono & Mapp (1995). A restatement and modification of Wells-Hering's laws of visual direction. Perception, 24, 237-252), and between physical and perceptual descriptions of visual direction (Ono, Ohtsuka & Lillakas (1998). Proceedings of the international workshop on advances in research on visual cognition, Tsukuba, Japan (pp. 125-136); Ono & Lillakas (1997). Proceedings of the fourth international display workshop, Nagoya, Japan (pp. 831-834)).

Methodological caveats for monitoring binocular eye position with nonius stimuli.

Three experiments, using two sets of Nonius lines placed in a random-dot stereogram, indicated that Nonius alignment does not always reflect binocular eye position and, thus, a caveat is necessary when Nonius alignment is used to monitor binocular eye position. We found that: (a) two Nonius lines with visual line values that differed by up to 7.6 min of arc can appear aligned; (b) the two lines of each of the two Nonius sets continued to appear aligned despite a change in vergence angle of 5.9 min of arc; and (c) the Nonius alignment reflected eye position better, when the binocular dots near the Nonius lines were eliminated.

A restatement and modification of Wells-Hering's laws of visual direction.

The laws of visual direction proposed by Wells some 200 years ago and Hering over 100 years ago are restated as three laws with the terminology of these two pioneers. This restatement serves both to honour their work and to strengthen some of the weaknesses in their original treatises. Second, two simple experiments, or tests of the laws, which the readers can readily perform by using their fingers as stimuli, are illustrated. Third, one of the three laws is modified to incorporate recent findings. Fourth, two recent experiments relevant to these new laws are described briefly, and their theoretical and methodological implications are discussed.

Visual localization of briefly presented peripheral targets.

Reported here are the results from two experiments designed to investigate Mateeff and Gourevich's (1983, 1984) claim that adult observers make large constant errors when judging the direction of briefly presented peripheral targets, with respect to a continuously visible scale. Experiment 1 involved a virtually exact duplication of Mateeff and Gourevich's paradigm. Experiment 2 involved adjusting the position of a light emitting diode (LED) so as to match the direction of a LED previously flashed in the periphery. No significant constant errors were found in either experiment.

The rhino-optical phenomenon: ocular parallax and the visible field beyond the nose.

One of the consequences of the noncoincidence of the nodal point and the center of rotation of the eye is the disappearance of targets near the limit of the nasal visual field when the monocular gaze is directed towards them. This ocular parallax phenomenon, which we measured in six adult subjects, is discussed in terms of its usefulness in demonstrating ocular parallax in a classroom situation. Also, a possible laboratory exercise is suggested.