Abstract
As the visual system ages, flicker sensitivity decreases and the latencies of cortical visual evoked potentials (VEP) increase. However, the extent to which these effects reflect age-related changes in the magnocellular (M) and or parvocellular (P) pathways remain unclear. Here, we investigated the relation between flicker fusion frequencies and VEP non-linearities induced by rapid stimulation, as a function of age over 6 decades. The approach, using Wiener kernel analysis of multifocal flash (mf)VEP, allows the extraction of signatures of both M and P processing and hence establishing a neural basis of the known decline in flicker fusion threshold. We predicted that, in a sample of 86 participants, age would be associated with a latency increase in early mfVEP response components and that flicker fusion thresholds, for both low and high contrast stimuli, would relate to the temporal efficiency of the M-generated VEP component amplitudes. As expected, flicker fusion frequency reduced with age, while latencies of early second order peaks of the mfVEP increased with age, but M temporal efficiency (amplitude ratio of first to second order peaks) was not strongly age-related. The steepest increases in latency were associated with the M dominated K2.1 (second order first slice) N70 components recorded at low and high contrast (6.7 and 5.9 ms/decade, respectively). Interestingly, significant age-related latency shifts were not observed in the first order responses. Significant decreases in amplitude were found in multiple first and second order components up to 30 years of age, after which they remained relatively constant. Thus, aging and decline in visual function appears to be most closely related to the response latencies of non-linearities generated by the M pathway.
Highlights
Changes in visual processing with age have been predominantly associated with temporal processing
Visually evoked potential (VEP) research shows an increase in the physiological latency of afferent input to primary visual cortex (V1) as a function of age, and as a function of the contrast, spatial frequency and temporal frequency of stimulation (Sokol and Moskowitz, 1981; Celesia et al, 1987; Porciatti et al, 1992; Tobimatsu et al, 1993; Emmerson-Hanover et al, 1994)
This study aimed to compare psychophysically measured flicker fusion thresholds and flash mfVEPs recorded from the cortical visual systems of individuals from 18 to 79 years in age, to investigate whether the behavioral decline in temporal processing with age can be linked to changing components of the two major visual pathways
Summary
Changes in visual processing with age have been predominantly associated with temporal processing Behavioral techniques such as flicker fusion frequency (McFarland et al, 1958; Tyler, 1989; Kim and Mayer, 1994) and visual inspection time (Deary et al, 2010) provide evidence of decrease in rate of visual processing with age and are more evident as cognitive load increases (Owsley, 2011; Ebaid et al, 2017). The question of whether any of the major retino-cortical pathways, i.e., magnocellular (M), parvocellular (P) or koniocellular (K), is more affected by aging, has not been reported in human EEG recordings
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