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Dagmar Wismeijer, Tomas Knapen, Raymond van Ee, Casper Erkelens; Influence of perspective and disparity on vergence smooth pursuit. Journal of Vision 2008;8(6):671. doi: 10.1167/8.6.671.
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We have investigated how perspective and disparity contribute to vergence smooth pursuit eye movements, when following a target's motion in depth (MID). It has previously been shown that vergence is produced in response to both disparity and sufficiently strong size cues, however, only with both cues defining the same MID direction . Here, we varied the two cues so as to also counteract one another to elucidate the relative efficacies of the two cues in driving vergence smooth pursuit eye movements.
The smooth pursuit target was an annulus surrounding fixation (3°–5°), consisting of dynamic or static random dots. The target performed periodic triangular MID with constant velocity (0.4Hz) and was displayed for the duration of one period. The MID was specified by applying changing binocular disparities and changing the size of the target (texture and size changed congruently). We varied the direction of MID defined by changing size while MID defined by disparity remained constant.
Vergence movements followed the changing disparity quite accurately, with an onset latency of 150ms, when both cues defined the same MID direction. However, vergence decreased as a function of the direction of MID defined by changing size. Results were independent of motion amplitude (100, 150 and 200 mm from screen depth). Dynamic dots had a slight negative influence on performance, because both changing size and disparity cues were degraded.
Our results show that both monocular cues and binocular cues significantly contribute to vergence. Although disparity is the main contributor, about 7–35% of vergence could be attributed to perspective.
 Erkelens C.J., Regan D., Human ocular vergence movements induced by changing size and disparity, J.Physiol. (1986), 379, pp.145-169.
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