Repetition priming is a form of implicit memory in which prior exposure to a stimulus facilitates the subsequent processing of that stimulus. While explicit memory has consistently been shown to decline with age, the effect of age on implicit memory remains unresolved. Most studies examining age-related effects on priming have utilized words or pictures of real objects with pre-existing representations that may differentially involve implicit and explicit memory processes across age groups. Repetition priming may also be influenced by attentional processes during encoding that are differentially affected by age. In a previous study using word-stem completion, we found that individual differences in cortical arousal, but not spatial attention, influenced the magnitude and temporal dynamics of conceptual priming in healthy older adults. The objective of this study is to investigate whether cortical arousal and spatial attention play differential roles in the magnitude and temporal dynamics of repetition priming in young and older adults using novel shapes that do not have pre-existing representations within memory.

Healthy young (n=25, M age=19.4) and older adults (n=54, M age=70.0) completed a perceptual repetition priming task that was followed by a recognition memory test and an alerting/spatial orienting task from which behavioral measures of cortical arousal and spatial attention were derived. Older adults also completed a battery of neuropsychological tests. In the perceptual priming task, participants made a speeded judgment on whether novel nonverbal shapes had “closed” or “open” perimeters. Each shape was presented twice: half following the first presentation (immediate repetition) and half after three intervening items (delayed repetition). Participants were then shown closed and open versions of each shape and asked to identify which version was presented in the previous task. In the alerting/orienting task, participants made a speeded response to the location of a visual target; on a subset of trials, either nonspatial alerting or spatial orienting cues were presented 300ms prior to the target.

Response times were slower and judgment accuracy greater in older adults (ps<0.05). However, the groups showed comparable levels of immediate and delayed repetition priming along with chance levels of recognition memory accuracy. Cortical arousal was reduced (p<0.001) and costs associated with spatial attention were larger (p<0.01) in the older adults. Despite comparable priming, cortical arousal and spatial attention were differentially related to priming across groups. In the young group, lower cortical arousal was associated with greater delayed priming (r=-.47, p=0.017) and slower decay rate (r=.44, p=0.03). In the older group, higher cost of spatial orienting was associated with greater immediate priming (r=.40, p=0.003) and faster decay rate (r=.29, p=0.03). Better category fluency performance was also associated with greater immediate priming (r=.32, p=0.035) and faster decay rate (r=.34, p=0.025) in older adults.

These findings suggest that different attentional systems support repetition priming across age groups. Priming is modulated by the efficiency of cortical arousal in young adults, but by the costs of spatial attention in older adults with reduced cortical arousal, consistent with a shift from bottom-up to top-down attentional processes and broader attentional scope with age.