Alistair P. Mapp

What does the dominant eye dominate? A brief and somewhat contentious review

We examine a set of implicit and explicit claims about the concept of eye dominance that have been made over the years and note that the new literature on eye dominance does not reflect the old literature from the first half of the last century. We argue that the visual and oculomotor function of the dominant eye—defined by such criteria as asymmetry in acuity, rivalry, or sighting—remains unknown and that the usefulness of the concept for understanding its function is yet to be determined. We suggest that the sighting-dominant eye is the eye used for monocular tasks and has no unique functional role in vision.

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.

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.

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-Herings 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)).

The cyclopean eye is relevant for predicting visual direction

Wells-Herings laws summarize how we process direction and predict that monocular stimuli appear displaced with respect to the viewer, but not with respect to other seen objects [Erkelens, C. J., & van Ee, R. (2002). The role of the cyclopean eye in vision: sometimes inappropriate, always irrelevant. Vision Research 42, 1157-1163] criticized this view and claimed that there is no perceptual displacement of these stimuli. We challenge their claim and improve on shortcomings of past studies. LEDs were monocularly presented to the observers, without their knowledge of which eye was being stimulated. Viewing distance was 9-10 cm; fixation distance was 30 cm. Observers reported the perceived relative and absolute directions of monocular stimuli. Our results are consistent with Wells-Herings laws.

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.

Visual localization of briefly presented peripheral targets

Reported here are the results from two experiments designed to investigate Mateeff and Gourevichs (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 Gourevichs 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.

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.

The Singular Vision of William Charles Wells (1757–1817)

William Charles Wells retained an interest in vision throughout his life. His first book was on single vision with two eyes; he integrated vision and eye movements to determine principles of visual direction. On the basis of experiments and observations he formulated three principles of visual direction, which can readily be demonstrated. In the course of these studies, he also examined visual acuity, accommodation and convergence, visual persistence, and visual vertigo. Insights into visual processing were mainly derived from observations of afterimages that were used to provide an index of how the eyes moved. His experiments enabled him to distinguish between the consequences of active and passive eye movements (later called outflow and inflow) as well as describing nystagmus following body rotation. After providing a brief account of Wellss life, his neglected research on vision is described and assessed.

The cyclopean illusion unleashed.

The cyclopean illusion is the apparent lateral shift of stationary stimuli on a visual axis that occurs when vergence changes. This illusion is predictable from the rules of visual direction. There are three stimulus situations reported in the literature, however, in which the illusion does not occur. In the three experiments reported here we examine those stimulus situations. Experiment 1 showed that an afterimage seen on a stimulus moving on the visual axis does not produce the illusion as reported in the literature but an afterimage seen on a screen does. Experiment 2 showed that the illusion occurs for an intermittently presented stimulus in contrast to what has been reported previously. Experiment 3 showed that a monocular stimulus presented against a random-dot background produced the illusion, also in contrast to what has been reported. The results were consistent with the rules of visual direction.