Dmax for Stereoscopic Depth Perception with Simulated Monovision Correction

in Seeing and Perceiving
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Purpose: Persons who wear monovision correction typically receive a clear image in one eye and a blurred image in the other eye. Although monovision is known to elevate the minimum stereoscopic threshold (Dmin), it is uncertain how it influences the largest binocular disparity for which the direction of depth can reliably be perceived (Dmax). In this study, we compared Dmax for stereo when one eye’s image is blurred to Dmax when both eyes’ images are either clear or blurred.

Methods: The stimulus was a pair of vertically oriented, random-line patterns. To simulate monovision correction with +1.5 or +2.5 D defocus, the images of the line patterns presented to one eye were spatially low-pass filtered while the patterns presented to the other eye remained unfiltered.

Results: Compared to binocular viewing without blur, Dmin is elevated substantially more in the presence of monocular than binocular simulated blur. Dmax is reduced in the presence of simulated monocular blur by between 13 and 44%, compared to when the images in both eyes are clear. In contrast, when the targets presented to both eyes are blurred equally, Dmax either is unchanged or increases slightly, compared to the values measured with no blur.

Conclusion: In conjunction with the elevation of Dmin, the reduction of Dmax with monocular blur indicates that the range of useful stereoscopic depth perception is likely to be compressed in patients who wear monovision corrections.

Dmax for Stereoscopic Depth Perception with Simulated Monovision Correction

in Seeing and Perceiving

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Figures

  • View in gallery

    An example of the random-line stimuli used in the experiments. The random lines shown here are of high (20%) density with +2.5 D of simulated blur in the upper half of the image presented to the right eye. Note that only the central two-thirds of the upper panel is binocularly correlated. Subjects reported whether the top half was near or far, relative to the bottom half. Free fusion of the left and rights panels provides a simulation of the monocular blur condition.

  • View in gallery

    Blurring of the random-line stimuli was accomplished by convolution of the unblurred lines with one of two blur functions, with the spatial kernels illustrated in the upper panels. This resulted in low-pass-filtered patterns with the average spectra shown in the two lower panels (+1.5 D of blur on the left and +2.5 D on the right).

  • View in gallery

    Dmin for monocularly and binocularly blurred stimuli were normalized for each subject with reference to the value of Dmin without blur. Taller bars indicate worse stereoscopic performance. Percentage changes were averaged across subjects for +1.5 D (top panel) and +2.5 D defocus (bottom panel). The data from 4 and 6 subjects contribute to the plotted averages for the +1.5 D and +2.5 D condition, respectively. Notice the difference in y-axis scaling between the two panels. Black and gray bars are for 5 and 20% density random lines, respectively. Error bars indicate between-subject standard errors.

  • View in gallery

    Dmax for monocularly and binocularly blurred stimuli were normalized for each subject with reference to the value of Dmax without blur. Negative values indicate a reduction in the range of stereoscopic vision. Percentage changes were averaged across subjects and plotted for +1.5 D (top panel) and +2.5 D defocus (bottom panel). The results for both the +1.5 and +2.5 D conditions include the data of 5 subjects.

  • View in gallery

    The effect of monocular blur on the linear depth interval is represented. The calculation of linear depth intervals using the average measured values of Dmax is based on formulae given by Schor and Flom (1969). The two eyes are shown at the bottom of each panel. Vertical bars indicate the useful range of binocular stereoscopic vision for unblurred (left of the fixation ‘×’) and monocular blurred (right of the fixation ‘×’) conditions, for near (left panel) and far (right panel) viewing distances. Within each panel, the inset illustrates the effect of monocular blur on the linear depth required to exceed the lower stereoscopic threshold (Dmin). Note the difference in horizontal and vertical scales in the two panels and in the insets. In the right panel the distal extent of the linear depth interval for the unblurred condition is truncated at 1500 cm. The reduction of Dmax with monocular blur has the effect of reducing the useful range of binocular stereoscopic vision. This figure is published in color in the online version.

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