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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 72, Iss. 7 — Jul. 1, 1982
  • pp: 871–877

Nonmotor component of fusional response to vertical disparity: a second look using an afterimage method

A. L. Duwaer  »View Author Affiliations

JOSA, Vol. 72, Issue 7, pp. 871-877 (1982)

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An afterimage method has been used to investigate the relative magnitudes of the nonmotor and motor components of the fusional response to vertical disparity in a complex visual stimulus of diameter 57° consisting of 50 horizontal lines and a square of side 2.5° in the middle. The largest vertical disparity that evokes a stable fusional response was found to be in the range 3–6°, of which the nonmotor component amounted only to 8–15′, i.e., 2–10% of the total. At these fusional amplitudes, binocular single vision was already disrupted in the foveola. When the 50 horizontal lines were omitted from the stimulus so that only the central square of side 2.5° remained, the fusional amplitudes decreased by only 25% while the absolute level of the nonmotor components remained the same. The non-motor components found here are much smaller than those (amounting to about 2°, or 25–40% of the total response) reported recently in the literature.

© 1982 Optical Society of America

A. L. Duwaer, "Nonmotor component of fusional response to vertical disparity: a second look using an afterimage method," J. Opt. Soc. Am. 72, 871-877 (1982)

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  1. A. E. Kertesz, "Effect of stimulus size on fusion and vergence," J. Opt. Soc. Am. 71, 289–293 (1981).
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  9. A. L. Duwaer and G. van den Brink, "Foveal diplopia thresholds and fixation disparities," Percept. Psychophys. 30, 321–329 (1982).
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  11. Fender and Julesz10 reported an extension of foveal diplopia thresholds (for horizontal disparity) by an order of magnitude up to 1.1° for binocularly stabilized bars and up to 2° for binocularly stabilized random-dot patterns (with a hidden square of side 1.37° and a relative horizontal disparity of 8′). This result would suggest a major change in retinal correspondence. In an attempt to demonstrate changes in retinal correspondence directly by using afterimages, Flom and Eskridge12 found that retinal correspondence remained stable to within the visual resolving power. Diner13 replicated the experiments of Fender and Julesz for binocularly stabilized bars and failed to obtain foveal diplopia thresholds beyond the classical limit of 0.4°. Crone and Hardjowijoto14 determined fusional limits for nonstabilized random-dot patterns (with a hidden square of side 13° and a relative horizontal disparity of 90′) and found values exceeding 2°. These limits were, however, based on the disappearance of global stereoscopic depth in the hidden square and not on disruption of singleness of local stimulus features in the fovea. It is well known that stereoscopic depth can be perceived in the presence of image doubling and during monocular image suppression, especially when the stimulus is scanned with the eyes, as was done by the subjects in the study of Crone and Hardjowijoto.15–18 Their fusional limits therefore can not be interpreted as foveal diplopia thresholds. As a result, Kertesz's findings seem to be the first confirmation of the results obtained by Fender and Julesz.
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  18. J. Linschoten, "Strukturanalyse der binokularen tiefenwahrnehmung," Ph.D. Thesis (University of Utrecht, Utrecht, The Netherlands, 1956).
  19. A. J. Duwaer, "Assessment of retinal image displacements during head movements using an afterimage method," Vision Res. (to be published).
  20. R. W. Ditchburn, Eye-Movements and Visual Perception (Clarendon, Oxford, 1973).
  21. A. L. Duwaer and G. van den Brink, "What is the diplopia threshold?" Percept. Psychophys. 29, 295–309 (1981).

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