Searching Semantic Memory as a Scale-Free Network: Evidence from Category Recall and a Wikipedia Model of Semantics

How is semantic memory structured and searched? Recalling items from semantic categories is a classic assay of semantic memory, and recall dynamics tend to exhibit semantic and temporal clustering, as if memory items are organized and retrieved in clusters. Recent analyses show this clustering to be approximately scale-free in terms of distributions of interresponse intervals (IRIs). This finding is replicated and extended in the present study by asking participants to type as many animals as they can recall from semantic memory. To begin to explain these results, the organization of semantic memory is modeled as a network based on Wikipedia entries for nearly 6,000 animals. The Wikipedia animal network is found to be scale-free in terms of its degree distribution, and aspects of the network are found to correlate with aspects of recall. Semantic similarity based on Wikipedia entries is found to compare favorably with a measure based on latent semantic analysis. It is concluded that semantic memory processes can be usefully theorized as searches over scalefree networks.