Impacts of older age on the temporal properties of collinear facilitation.

Collinear facilitation is a visual phenomenon by which the contrast detection threshold of a central target is reduced (facilitation) when placed equidistant between two high-contrast flankers. The neural mechanisms underpinning this phenomenon originate from feed-forward lateral facilitation between cell layers in V1 (slower) and feedback facilitation from extrastriate visual areas to V1 (faster). The strength of these contributions has been explored in younger adults by presenting the central target and flankers at varying timing offsets. Here, we investigated the effects of older age on collinear facilitation with flankers presented in sync, before, and after target onset, to allow the inference of any characteristic effect of older age on feed-forward and feedback facilitatory mechanisms. Seventeen older and 19 younger observers participated. Our data confirms previous findings of an age-related reduction in facilitation when flankers and target occur at synchrony, but no age difference was found at other timings. Marked interindividual variability in facilitation for the different flanker onset timings was present, which was repeatable within individuals. Further research is required to ascertain the mechanistic underpinnings for different facilitation profiles between individuals. Longitudinal study across an individual's life span is needed to determine whether an individual's facilitation profile changes with age.