Abstract
Purpose. Vision Research will soon publish a paper by Erkelens and van Ee that claims the cyclopean eye in vision is irrelevant. To counter this claim, we conducted an experiment to explore and clarify two possible meanings of perceived direction, absolute and relative, and to examine how each meaning relates to their claim. Method. We presented pairs of LEDs on either one or both visual axes in three conditions: (a) “Double monocular”—both eyes were open and both pairs of LEDs were presented, (b) “Monocular with two eyes open”—the pair of LEDs for the right eye or the pair for the left eye was presented, and (c) “Monocular with one eye closed”—the same as (b) but the non-viewing eye was closed. The near LED of each pair was presented 2 cm in front of the face so that observers could report its absolute direction with reference to different parts of the face, for example, in front of the eye, and they could also report its relative direction with respect to a more distant LED. Results. The near LEDs were rarely seen in front of either eye as expected from Erkelens and van Ee's discussion. There were only two such reports out of the 72 reports made by our 12 observers. The most common report was that the near LED appeared either directly in front of the nose or very near the middle of it. Both pairs of LEDs were reported to be in the same relative direction (i.e., one on top of the other). Conclusion. We conclude that (a) their claim applies to relative direction but not to absolute direction, and (b) their claim about the cyclopean eye is unwarranted, because the absolute direction of a stimulus on the visual axis of one eye appears on the common axis, as shown in this study and many other studies since the time of Ptolemy, circa 100-170.