Aging delays the formation of object representations

Aging commonly slows down behavioral task performance in humans. However, it remains unknown how aging affects the neural dynamics of processing visual information, required for most tasks. Here, we investigate age-related delays in the formation of object representations and the processing stages at which these delays manifest. For this, we measured EEG and fMRI in healthy younger (18-35 years, N=21) and older participants (60-75 years, N=22) while they viewed natural images. We applied three advanced multivariate techniques to analyze the formation of object representations. First, we decoded object identity in a time-resolved manner to quantify age-related processing delays. Our results reveal significant differences in decoding time courses between both age groups in an early time window (around 80-155 ms). Specifically, decoding time courses peaked significantly later (around 20 ms for different categorical comparisons) in older adults. These findings suggest delayed feedforward processing in aging. Second, we compared the representations underlying the observed delay in younger and older adults using RSA. Our results reveal that both age groups are characterized by time-shifted yet similar representations. Third, we linked the observed EEG patterns to fMRI signals in ventral visual stream regions through EEG-fMRI fusion. This allowed us to map temporal delays to cortical processing stages. We observed that age-related delays manifest in mid- and high-level regions (i.e., V3, LOC, FFA) rather than early visual areas (i.e., V1, V2). In summary, our findings reveal age-related changes in the temporal dynamics of object representations. By quantifying a temporal delay as well as linking it to mid-to-high level ventral visual cortex, our results provide a first nuanced view on the lifespan plasticity of visual object representations.