Abstract
The influence of normal aging in early, intermediate and high-level visual processing is still poorly understood. We have addressed this important issue in a large cohort of 653 subjects divided into five distinct age groups, [20;30[, [30;40[, [40;50[, [50;60[and [60;[. We applied a broad range of psychophysical tests, testing distinct levels of the visual hierarchy, from local processing to global integration, using simple gratings (spatial contrast sensitivity -CS- using high temporal/low spatial frequency or intermediate spatial frequency static gratings), color CS using Landolt patches, moving dot stimuli (Local Speed Discrimination) and dot patterns defining 3D objects (3D Structure from Motion, 3D SFM). Aging data were fitted with linear or quadratic regression models, using the adjusted coefficient of determination (R2 a) to quantify the effect of aging. A significant effect of age was found on all visual channels tested, except for the red-green chromatic channel. The high temporal low spatial frequency contrast sensitivity channel showed a mean sensitivity loss of 0.75 dB per decade (R2 a = 0.17, p<0.001), while the lower intermediate spatial frequency channel showed a more pronounced decrease, around 2.35 dB (R2 a = 0.55, p<0.001). Concerning low-level motion perception, speed discrimination decreased 2.71°/s (R2 a = 0.18, p<0.001) and 3.15°/s (R2 a = 0.13, p<0.001) only for short presentations for horizontal and oblique meridians, respectively. The 3D SFM task, requiring high-level integration across dorsal and ventral streams, showed the strongest (quadratic) decrease of motion coherence perception with age, especially when the task was temporally constrained (R2 a = 0.54, p<0.001). These findings show that visual channels are influenced by aging into different extent, with time presenting a critical role, and high-level dorso-ventral dominance of deterioration, which accelerates with aging, in contrast to the other channels that show a linear pattern of deterioration.
Highlights
Gradual decline of visual function is a feature of normal aging
To understand how aging affects the visual function across multiple organization levels we have used low-level stimulation paradigms that preferentially activate the red-green (P) and blueyellow (K) channels, an achromatic channel tuned to Intermediate Spatial Frequencies (ISF [31,32,33]); a achromatic channel biased for the M pathway (Frequency Doubling Technology testing, FDT [32]); and a local motion perception (Mbiased) channel (Local Speed Discrimination Test, local speed discrimination (LocSp) [34,35])
We measured achromatic contrast sensitivity (CS) at an intermediate spatial frequency for nine visual field locations and found a highly significant effect of aging on mean CS [F(4,164) = 53.09, p,0.001]
Summary
Gradual decline of visual function is a feature of normal aging. This partly results from the combination of optical factors, retinal neural factors such as photoreceptor and ganglion cell degeneration and cortical factors [1,2]. We attempted to address this issue using a hierarchical approach from the point of view of visual processing and stimulus construction In this way we used chromatic and achromatic contrast sensitivity tasks with simple gratings and patches, motion discrimination tasks with simple random dots kinetograms (RDKs), and high-level object integration tasks using the same type of dots. To understand how aging affects the visual function across multiple organization levels we have used low-level stimulation paradigms that preferentially activate the red-green (P) and blueyellow (K) channels (chromatic CS approach, Cambridge Color Test, CCT [28,29,30]), an achromatic channel tuned to Intermediate Spatial Frequencies (ISF [31,32,33]); a achromatic channel biased for the M pathway (Frequency Doubling Technology testing, FDT [32]); and a local motion perception (Mbiased) channel (Local Speed Discrimination Test, LocSp [34,35]). This task targets dorsal stream function and dorso-ventral integration for object recognition [3,36]
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