Proceedings of the Annual Meeting of the Cognitive Science Society

Double dissociations were long considered a gold standard for establishing functional modularity. However, Plaut (1995) demonstrated that double dissociations could result without underlying modularity. He damaged attractor networks with separate orthographic and semantic layers (as well as a hid- den layer with feedback connections from semantics) that were trained to map orthography to semantics. Damaging con- nections coming from either the orthographic layer or recur- rent semantic connections (to and from cleanup units) could both yield double dissociations, with some models exhibit- ing greater relative deficits for abstract words, and others for concrete words. We investigated whether double dissocia- tions would emerge in a simpler attractor network with 2 sets of units (orthographic and semantic) and 2 layers of connec- tions (orthographic-to-semantic and recurrent semantic con- nections). Random damage to orthographic-semantic con- nections yielded double dissocations (some damaged mod- els showed stronger relative deficits for abstract words, while others showed stronger relative deficits for concrete words). Semantic-semantic damage led only to concrete deficits. The presence of double dissociations given different degrees of damage in each model reconfirm Plaut's (1995) findings in simpler, “flat” attractor network (O'Connor, Cree, & McRae, 2009), with less potential for modularity. The tendency for concrete impairments given damage to the semantic attractor level is at once surprising and revealing; it demonstrates a di- vision of labor (and partial modularity) that emerges in this network. We will discuss theoretical implications, as well as next steps in this research program.