Effects of aging on successful object encoding:Enhanced semantic representations compensate for impaired visual representations

Abstract

Whereas episodic memory and visual processing decline substantially with healthy aging, semantic knowledge is generally spared. There is evidence that older adults can take advantage of their spared semantic knowledge to support their performance in episodic memory and visual tasks. Here, we used fMRI combined with representational similarity analyses (RSA) to examine how visual and semantic representations stored during encoding predict subsequent object memory. Young and older adults encoded images of objects during fMRI scanning and recalled these images while rating the vividness of their memories. After scanning, participants discriminated between studied images and similar lures. RSA based on a deep convolutional neural network and normative concept feature data was used to link patterns of neural activity during encoding to visual and semantic representations. The quality of visual representations was reduced in older adults, consistent with dedifferentiation, whereas the quality of semantic representations was enhanced in older adults, consistent with hyperdifferentiation. Despite dedifferentiation, visual representations stored in early visual cortex predicted later recall with high vividness in both young and older adults, with no age-related differences. In contrast, semantic representations in lingual and fusiform gyrus were associated with better subsequent object picture recall in older but not in young adults. This finding is consistent with evidence that older adults rely on semantic knowledge to compensate for cognitive deficits. Taken together, the results suggest that the age-related neural dedifferentiation for visual information in posterior regions might be partly counteracted by a boost on semantic representations in more anterior areas. Significance StatementPrevious research has shown that healthy aging tends to impair memory for individual events, visual processing, and other cognitive abilities but not semantic knowledge. We investigated the effects of aging on the quality of the information stored in the brain when viewing common objects and on how this information enables subsequent memory for these objects. Using fMRI combined with modeling of the stimuli, we found that visual information was degraded in older adults, but it was sufficient to support subsequent memory. In contrast, semantic information supported subsequent memory only in older adults. This is the first direct neuroscience evidence that older adults take advantage of spared semantic representations to boost their memory for individual events.