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Fangfang Yan, Fang Hou, Ge Chen, Zhong-Lin Lu, Chang-Bing Huang; Aging affects gain but not internal noise in the visual system. Invest. Ophthalmol. Vis. Sci. 2014;55(13):766.
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Visual functions decline with age but how aging degrades visual functions remains controversy. In the current study, the mechanisms underlying aging in the visual system was examined.
We developed an efficient procedure based on the qCSF (Lesmes, et al, 2010) to measure contrast sensitivity as functions of seven spatial frequencies (0.5~8 cpd) in three levels of external noise (white noise, μ=0 and σ∈[0 .08 0.24]) in young and old subjects. Using the perceptual template model (PTM) (Lu & Dosher, 2008), we decomposed contrast sensitivity into internal additive noise, internal multiplicative noise, template gain, and system non-linearity, and analyzed the mechanisms underlying CSF changes associated with aging. Five young (age: 23.6±0.8 yrs) and five old (age: 70±2.0 yrs) subjects, all without ophthalmological and mental diseases, participated in the experiment.
We found that contrast sensitivity varied significantly with spatial frequency (F(6, 48)=43.316, p<0.001), level of external noise (F(2, 16)=227.05, p<0.001), and age (F(1, 8)=75.657, p<0.001). Nested model comparison revealed that only internal additive noise and the gain of the perceptual template varied significantly with spatial frequency in both groups. The model accounted for 89% of the variance in the data. The template gain decreased significantly with aging (F(1, 8)=10.083, p<0.05), but the internal noise was comparable between the two groups (F(1, 8)=2.257, p>0.05).
Our results suggest that aging decreases template gain but does not change internal noise in the visual system. Quick characterization of CSF at different noise levels and the accompanying analysis developed in the current study may have wide applications in other clinical populations.
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