Biology subjects

Naspi, L.

Publications and source records attributed to Naspi, L..

2 recordsLinked to original sources

bioRxiv2022

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

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.

neuroscience↗

bioRxiv2021

Perceptual and Semantic Representations at Encoding Contribute to True and False Recognition of Objects

When encoding new episodic memories, visual and semantic processing are proposed to make distinct contributions to accurate memory and memory distortions. Here, we used functional magnetic resonance imaging (fMRI) and representational similarity analysis to uncover the representations that predict true and false recognition of unfamiliar objects. Two semantic models captured coarse-grained taxonomic categories and specific object features, respectively, while two perceptual models embodied low-level visual properties. Twenty-eight female and male participants encoded images of objects during fMRI scanning, and later had to discriminate studied objects from similar lures and novel objects in a recognition memory test. Both perceptual and semantic models predicted true memory. When studied objects were later identified correctly, neural patterns corresponded to low-level visual representations of these object images in the early visual cortex, lingual, and fusiform gyri. In a similar fashion, alignment of neural patterns with fine-grained semantic feature representations in the fusiform gyrus also predicted true recognition. However, emphasis on coarser taxonomic representations predicted forgetting more anteriorly in ventral anterior temporal lobe, left perirhinal cortex, and left inferior frontal gyrus. In contrast, false recognition of similar lure objects was associated with weaker visual analysis posteriorly in early visual and left occipitotemporal cortex. The results implicate multiple perceptual and semantic representations in successful memory encoding and suggest that fine-grained semantic as well as visual analysis contributes to accurate later recognition, while processing visual image detail is critical for avoiding false recognition errors. Significance StatementPeople are able to store detailed memories of many similar objects. We offer new insights into the encoding of these specific memories by combining fMRI with explicit models of how image properties and object knowledge are represented in the brain. When people processed fine-grained visual properties in occipital and inferior temporal cortex, they were more likely to be recognize the objects later, and less likely to falsely recognize similar objects. In contrast, while object-specific feature representations in fusiform predicted accurate memory, coarse-grained categorical representations in frontal and temporal regions predicted forgetting. The data provide the first direct tests of theoretical assumptions about encoding true and false memories, suggesting that semantic representations contribute to specific memories as well as errors.

neuroscience↗