Population aging is taking place in every country in the world, which would cause far-reaching socioeconomic consequences. Ageing affects almost all cognitive systems, but the exact characteristics and mechanisms of the resulting functional degradation are still missing. In the current study, by combining psychophysics and computational modeling, we investigated pattern(s) of age-related visual declines, psychophysical mechanism, and the potential of perceptual learning in recovering degraded functions.
The experimental research consisted of three studies. In Study 1, we built a test battery of visual functions and systematically evaluated the relationship among visual functions, visual declines, visual declines and higher cognitive functions, and the influence of visual declines on the quality of daily life. Study 2 focused on the psychophysical mechanisms (e.g. hypothesis of noise elevation) of visual declines. Study 3 was to explore the potential of training at cutoff spatial frequency in improving contrast sensitivity and visual acuity in old population.
We found that 1) aging affects most but not all visual functions; The magnitudes of visual declines varied across tested functions; There are correlations between some of the age-related declines and between visual and cognitive declines; 2) the associative pattern (both number of correlation and the magnitude of correlation) among the tested functions were enhanced in old adults; 3) the mutually explanatory power among visual functions and among visual functions and cognitive functions was significantly elevated in the elderly; 4) the useful field of view (UFOV) was the critical index function to distinguish between young and old (98.3%); 5) The age-related visual deficits significantly affected near and far activities in daily life.
The degradation of spatial contrast sensitivity function was attributed to the decrease of template gain at all spatial frequencies and increase of internal noise at higher spatial frequencies in the visual system, which partly supported the noise hypothesis.
Perceptual learning paradigm that targets high frequency deficits in contrast sensitivity in presbyopia significantly improved contrast sensitivity at the trained spatial frequency. Moreover, the effect transferred to contrast sensitivity over a wide range of spatial frequencies and visual acuity in both eyes. The improvements were not due to improved optical transmission.
The relative results will help to understand the pattern and mechanisms of visual ageing, provide theoretical basis of visual rehabilitation in the aged, and shed light upon researches in pathological aging.