Motion perception is affected by healthy aging, which impairs the ability of older adults to perform some daily activities such as driving. The current study investigated the underlying causes of age-related motion contrast sensitivity losses by using an equivalent noise paradigm to decompose motion contrast sensitivity into calculation efficiency, the temporal modulation transfer function (i.e., temporal blur) and 3 sources of internal noise: stochastic absorption of photons by photoreceptors (i.e., photon noise), neural noise occurring at the retinal level (i.e., early noise) and at the cortical level (i.e., late noise). These sources of internal noise can be disentangled because there impacts on motion contrast sensitivity vary differently as a function of luminance intensity. The impact of healthy aging on these factors was evaluated by measuring motion contrast sensitivity of young and older healthy adults at different luminance intensities, temporal frequencies and with/without external noise. The older adults were found to have higher photon noise, which suggests a lower photon absorption rate of cones. When roughly equating the amount of photons being absorbed by the photoreceptors, older adults had lower calculation efficiencies, but no significant aging effect was found on temporal modulation transfer function, early noise and late noise.

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Age-related decline in visual perception is usually attributed to optical factors of the eye and neural factors. However, the detection of light by cones converting light into neural signals is a crucial intermediate processing step of vision. Interestingly, a novel functional approach can evaluate many aspects of the visual system including the detection of photons by cones. This approach was used to investigate the underlying cause of age-related visual decline and found that the detection rate of cones was considerably affected with healthy aging. This functional test enabling to evaluate the detection of photons by cones could be particularly useful to screen for retinal pathologies affecting cones such as age-related macular degeneration. However, the paradigm used to functionally measure the detection of photons was complex as it was evaluating many other properties of the visual system. The aim of the current mini review is to clarify the underlying rationale of functionally evaluating the detection of photons by cones, describe a simpler approach to evaluate it, and review the impact of aging on the detection rate of cones.