Abstract
A statistical analysis of semantic memory should reflect the complex, multifactorial structure of the relations among its items. Still, a dominant paradigm in the study of semantic memory has been the idea that the mental representation of concepts is structured along a simple branching tree spanned by superordinate and subordinate categories. We propose a generative model of item representation with correlations that overcomes the limitations of a tree structure. The items are generated through “factors” that represent semantic features or real-world attributes. The correlation between items has its source in the extent to which items share such factors and the strength of such factors: if many factors are balanced, correlations are overall low; whereas if a few factors dominate, they become strong. Our model allows for correlations that are neither trivial nor hierarchical, but may reproduce the general spectrum of correlations present in a dataset of nouns. We find that such correlations reduce the storage capacity of a Potts network to a limited extent, so that the number of concepts that can be stored and retrieved in a large, human-scale cortical network may still be of order 107, as originally estimated without correlations. When this storage capacity is exceeded, however, retrieval fails completely only for balanced factors; above a critical degree of imbalance, a phase transition leads to a regime where the network still extracts considerable information about the cued item, even if not recovering its detailed representation: partial categorization seems to emerge spontaneously as a consequence of the dominance of particular factors, rather than being imposed ad hoc. We argue this to be a relevant model of semantic memory resilience in Tulving’s remember/know paradigms.
Highlights
One of the most fascinating aspects of the human brain is its ability to ascribe significance to and recognize meaning in objects and events, and more generally to make sense of the world
The relatively much simpler network structure of the hippocampus, in particular of its CA3 field, where episodic memories have long been thought to be at least initially represented by unique patterns of neural activity, may lead to the limited set of outcomes of episodic memory retrieval: either the pattern is retrieved, or not
Retrieval, subjects remember what happened in the episode, in the second they do not, they may still know many of the elements in the episode, likely as they reconstruct them with input from semantic memory
Summary
One of the most fascinating aspects of the human brain is its ability to ascribe significance to and recognize meaning in objects and events, and more generally to make sense of the world. Semantic memory, comprising our acquired knowledge about the world, can be imagined to reflect, in its statistical structure, the complex, distributed, policentric structure of the neocortex where it resides. Retrieval, subjects remember what happened in the episode, in the second they do not, they may still know many of the elements in the episode, likely as they reconstruct them with input from semantic memory. This is the basis for remember/know paradigms [1] that assess hippocampal contribution to memory retrieval. How can the statistical structure of the memory representations themselves be characterized?
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