Neuroanatomical and cognitive mediators of age-related differences in perceptual priming and learning

Abstract

Our objectives were to assess age differences in perceptual repetition priming and perceptual skill learning and to determine whether they are mediated by cognitive resources and regional cerebral volume differences. Fragmented picture identification paradigm allows the study of both priming and learning within the same task. The authors presented this task to 169 adults (ages 18-80), assessed working memory and fluid intelligence, and measured brain volumes of regions that were deemed relevant to those cognitive skills. The data were analyzed within a hierarchical path modeling framework. In addition to finding age-related decrease in both perceptual priming and learning, the authors observed several dissociations with regards to their neural and cognitive mediators. Larger visual cortex volume was associated with greater repetition priming, but not perceptual skill learning, and neither process depended upon hippocampal volume. In contrast, the volumes of the prefrontal gray and white matter were differentially related to both processes via direct and indirect effects of cognitive resources. The results indicate that age-related differences in perceptual priming and skill learning have dissociable cognitive and neural correlates.

Figure 1

Illustration of regions of interest manually traced from structural MRI scans. A) Prefrontal cortex – dorsolateral, orbitofrontal, and white matter; B) Caudate nucleus; C) Hippocampus; D) Fusiform gyrus; E) primary visual cortex (calcarine).

Figure 2

Example of stimulus with various levels of fragmentation, ranging from Level 1 (very fragmented) to Level 8 (complete picture). Pictures are shown as they appeared to the participants.

Figure 3

Identification thresholds (IT) for baseline, old, and new line drawings across the lifespan. Note that lower IT reflects better performance. Old items & Age: t = 5.99, p < .001, b = .42; New items & Age: t = 2.19, p < .05, b = .17.

Figure 4

Path analysis model for Reduced Model II which provided the best fit for the data. All path parameters are standardized coefficients. Curved double-headed arrows represent correlations and straight directional arrows represent estimated paths. Age exerted a negative direct effect on perceptual priming, but all effects of age on perceptual learning were mediated by neural and cognitive factors. Priming had a strong effect on learning. LPFC – lateral prefrontal cortex volume; Fwhite – prefrontal white matter volume; VC – primary visual cortex; WMv – verbal working memory composite; WMnv – nonverbal working memory composite; Gf – fluid intelligence composite; Train – fragmented picture identification threshold for training set; Prime – fragmented picture identification threshold for repeated set; Learn – fragmented picture identification thereshold for novel picture set. See text and Table 3 for model fit indices and Table 2 for variable descriptive statistics.

Figure 5

Effect of primary visual cortex volume on identification of fragmented pictures. Regressions lines correspond to baseline set, repeated pictures, and novel pictures. Note that lower identification thresholds indicate better performance. Visual cortex volume is associated with repeated but not novel object identification thresholds. Old items & VC: t = −2.06, p < .05, β = −.14; New items & VC: t = −.95, ns, β = −.07.