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H.L. Humble, P. Ghude, M.J. Leys, J.V. Odom; Effects of Visual Noise on Heading Perception in Optic Flow Patterns . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2305.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the effects of visual noise on the precision and bias of heading judgments as a function of age and central visual field loss in elderly patients with age–related macular degeneration (AMD).
Three groups of observers made heading judgments using a relatively standard optic flow display. The groups were younger normals aged 21–50 years, older normals aged =<60 years and low vision patients with AMD aged =<60 years. Observers were seated 50 cm from a display that subtended 44.6 arc deg in the horizontal dimension. The observer saw a red line at the center of the screen. Pressing a mouse began a trial. During the 833 mS trial, an optic flow pattern of 100 white dots on a black background appeared at random locations and moved away from a focus of expansion (FOE). 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’ task was to determine if the FOE was to the right or left of the red line. A 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 defined as ½ the difference of the thresholds. Observers repeated the judgments under 4 conditions: a no noise conditions and 3 conditions in which the individual flow vectors were perturbed by Gaussian directional noise along the x–axis. The standard deviation of the noise varied from 0.92 to 2.75 deg.
As the standard deviation of directional noise increased the precision thresholds for the young normal and older normal groups remained constant at about 2.18 and 3.69 deg., respectively. In the absence of noise, the precision of AMD patients was 3.91 arc degrees and not different from that of older normals (p > 0.1). As noise increased precision thresholds of AMD patients with AMD increased to 8.76 arc deg. in a linear fashion (r = 0.46; p < 0.01).
Age has an effect on the precision but not the bias of heading judgments. AMD does not have a major impact on either precision or bias in the absence of noise. However, directional noise results in a dramatic impairment in the precision of heading judgments in optic flow fields for patients with AMD.
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