Interaction between Accommodation and Vergence on Distance Perception

Fisher and Ciuffreda (1988) and Mon-Williams and Tresilian (1999) reported that, without vergence cue, diopter change in accommodation induced change in apparent distance. Meanwhile, there is conflicting evidence about the relative roles of accommodation and vergence in distance perception (Richards & Miller, 1969; von Holst, 1973). In the current study, we investigated interaction between accommodation and vergence on distance perception. The perceived distance from integration of vergence evoked by a fixation target and accommodation by a pair of concave or convex lenses in front of eyes is measured with a mirror stereoscope. The stimulus was a white square with a black cross-shaped fixation on a black background. In dark surroundings, subjects were asked to commit the apparent distance of the target to memory, and then without the lenses, re-create the distance by changing distance of another fixation target. The apparent size of the target through lenses were equivalent to the size without lenses. The results showed that not only vergence but accommodation affect the apparent distance, and they were summed linearly.