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M. J. Leys, P. Ghude, J. V. Odom; Masking Effects of Laminar Flow on Heading Perception in Normals and Patients With Age-Related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5505.
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To determine the effects of masking by laminar flow on the bias and precision of heading judgments in patients with central visual field loss due to age-related macular degeneration (AMD) as compared to young and old normals.
Three groups of subjects were tested; younger normals aged 21-50 years, older normals aged 60 years or more and low vision patients with AMD aged 60 years or more. Observers were seated 50 cm from a display that subtended 44.6 arc deg in the horizontal dimension. Observers saw a red line at the center of the screen. Pressing a mouse button began a of 833 mS trial during which the stimulus was an optic flow pattern of 100 white dots on a black background. Fifty dots appeared at random locations and moved away from a focus of expansion (FOE). An additional 50 dots moved across the screen. Dots had a lifetime of 467 mS or were replaced as they moved off of the screen. At the end of the trial the central red line reappeared. The observers’ pressed either the left or right mouse button to indicate if the FOE was to the right or left of the red line. An interleaved double staircase was employed to determine a threshold for the FOEs to the right and to the left of the center. Bias was the sum of the right and left thresholds. Precision was ½ the difference of the thresholds. Observers repeated the judgments twice, once as the laminar flow moved from left to right and once when it moved from left to right.
Observers’ heading judgments shifted toward the direction of laminar flow. However, the shift in bias was not statistically different between young normal and AMD groups. On average the shift was about 4.9 deg. Laminar flow impaired the precision of heading judgments. The mean precision of the younger normals was 2.32 deg, of the older normals 4.19 deg and of AMD patients 7.21 deg (p ≤ 0.0004).
As previously reported, laminar flow changes the bias of heading judgments. AMD does not cause a significant change in bias. Age and AMD do, however, lead to impaired precision of heading judgments when radial flow targets are masked by laminar flow. The results suggest that extraneous moving objects in the visual field impair heading judgments of older people and, especially, AMD patients.
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