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.

Context-Dependent Effect (CDE) is a process by which restoring the original learning context enhances recall ability of the material being studied. One type of context is body expressions. Memory is one of the most common areas affected by Traumatic Brain Injury (TBI). However, although the performance of people with TBI is lower than that of healthy people in most memory-related parameters, both groups show evidence for CDE. We examined the CDE via behavioral and eye movement measures.

Twenty-four healthy individuals and 27 patients with moderate-tosevere TBI participated in a memory task. Participants were exposed to pictures of people with neutral facial expression and neutral body expression and were asked to remember them for a subsequent memory test. In the testing session, they were asked to determine whether or not the person presented to them had appeared before, under two conditions: (1) where the context remains constant (facial expression and body expression remained neutral- the Repeat condition) (2) where the context changes (facial expression remained neutral and the body changed to angry or happy expression - the Re-pair condition).

While memory of the individuals with TBI was poorer than that of the control group, both groups exhibited CDE, as this effect was stronger in the Repeat condition compared to the Re-pair angry condition. We found that participants spent most of their time looking at the head. In addition, in both groups, we found a CDE and a group effect with regard to the difference in Dwell Time, so DT toward faces in the Repeat condition was higher than toward faces in the Re-pair condition. Also, DT toward correctly recognized people was higher among the control group than the TBI group. This effect appeared in the study and test phases.

This study supports previous research showing evidence for CDE using body expression in the TBI group, like the control group, and extends our comprehension of the relationship between eye movements, memory, and context of facial and body expression.