Implications of distributed representations for semantic processing: Evidence from Alzheimer's disease

Prior work by Gonnerman and colleagues presented a theory of semantic processing in normal and impaired populations. Their account incorporates distributed representations and predicts a complex relationship between semantic knowledge and naming ability. According to this account, during the course of progressive brain damage, one should observe different relationships between damage to semantic knowledge and naming ability for natural kinds versus artifacts. For artifacts, the theory predicts that naming ability will not be strongly correlated with damage to semantic category structure, whereas for natural kinds the nature of the relationship will change as damage to the system progresses. To test this theory, young and elderly participants and patients with Alzheimer's disease named a series of pictures and completed a board sorting task, in which they placed words from a semantic category on a two dimensional grid in a way that represented their inter-similarities, thus reflecting the nature of their semantic knowledge. Results confirmed the prediction that a strong relationship between picture naming and disrupted category structure is evident only for natural kinds categories at later stages of damage. For natural kinds in earlier stages and artifacts throughout the progression of the disease, disrupted category structure is not directly reflected in naming performance. These data point to a complex relationship between the underlying category structure and its realization in naming ability.