What exactly are the differences between semantic and lexical-semantic networks?
"semantic network" is way of representing "semantic" relations in form of a "graph" . where as "lexical semantic network" is a type of semantic network which represents the relations between words , sub-words or some-other linguistic related terms. so in other words , lexical semantic networks are a type of semantic networks dealing with language relationships.
According to Wikipedia and Semantic Networks ,By John F. Sowa This is an updated version of an article in the Encyclopedia of Artificial Intelligence, Wiley, 1987, second edition, 1992.
A semantic network is used when one has knowledge that is best understood as a set of concepts that are related to one another.
Most semantic networks are cognitively based. They also consist of arcs and nodes which can be organized into a taxonomic hierarchy. Semantic networks contributed ideas of spreading activation, inheritance, and nodes as proto-objects.
On the other hand, Lexical semantic:
...explores whether the meaning of a lexical unit is established by looking at its neighborhood in the semantic net (words it occurs with in natural sentences), or whether the meaning is already locally contained in the lexical unit.