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S. W. Chat, R. W. Li, E. Jang, D. Levi; Reduced Sampling Efficiency Can Explain the Elevated Vernier Threshold With Aging: Vernier Acuity in Positional Noise. Invest. Ophthalmol. Vis. Sci. 2010;51(13):966.
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© ARVO (1962-2015); The Authors (2016-present)
Li et. al. (2000 & 2001) reported that Vernier acuity decreases with increasing age. However, the underlying neural mechanism is still not clear. In this experiment, we investigated the age-related changes in Vernier processing on the basis of a theoretical noise model. Specifically, we evaluated Vernier performance in positional noise and further investigated how aging affects the underlying processing components.
Vernier acuity in noise was measured in both younger (21-40-yr-old; mean age=25.1 years; n=15) and older (60-85-yr-old; mean age=67.2 yrs; n=17) subjects. All our subjects had normal visual acuity. The task was to judge which of three pairings of two groups of 10 discrete white dots (segment length: 19 arcmin; gap size: 4 arcmin) was misaligned. Viewing distance was 8 m (inter-pixel distance: 5 arcsec). An interleaved staircase method was used to track the individual thresholds. Threshold was defined as the Vernier offset at which 66% correct responses were obtained. Positional noise was produced by distributing the individual dots of each line segment according to a Gaussian probability function. By measuring the thresholds in different external noise settings (0, 0.17, 0.33 & 0.67 arcmin), both internal positional noise and sampling efficiency can be estimated by fitting the response data with a positional averaging model.
Mean Vernier thresholds were significantly elevated by 20% in the older age group when compared to the younger age group (p<0.005 in all 4 tested noise conditions). Our modeling shows that the mean sampling efficiency was significantly reduced by 50% in our older subjects, while the mean internal noise was comparable between the two age groups.
Here we show that Vernier threshold in positional noise was elevated with advancing age. The deterioration in Vernier acuity is primarily the result of the degraded sampling efficiency, with internal noise remaining unchanged. The present findings contribute to our understanding of Vernier processing in the aging visual system.
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