Stochastic approaches to understanding dissociations in inflectional morphology  

Oleh:

Plunkett, Kim ; Bandelow, Stephan

Jenis: Article from Journal - ilmiah internasional
Dalam koleksi: Brain and Language (Full Text) vol. 98 no. 2 (2006), page 194-209.
Topik: Double dissociation; Inflectional morphology; Past tense; English plurals; Connectionist models; Neural networks; Aphasia; Alzheimer’s disease; Parkinson’s disease; Single case studies
Fulltext: 98_02_Plunkett.pdf (528.85KB)

Isi artikel

Computer modelling research has undermined the view that double dissociations in behaviour are suYcient to infer separability in the cognitive mechanisms underlying those behaviours. However, all these models employ multi-modal representational schemes, where functional specialisation of processing emerges from the training process. Targeted lesioning of diVerent regions of functional specialisation leads to varied but predictable deWcits in model performance. We argue that multi-modal representational schemes are not a necessary condition for the observation of double dissociations in an information processing system that shares resources across multiple tasks. Using a uni-modal representational system, we demonstrate that double dissociations may also result from stochastic processes. Lesioning experiments on a single-route, uni-modal connectionist model of regular and irregular noun and verb morphology conWrm and extend earlier work demonstrating that selective impairment across tasks can result from damage to a distributed information processing system. A systematic investigation of the degree to which performance deteriorates across diVerent inXectional classes reveals that simple and double dissociations can occur in this single-route, uni-modal model. An important prediction of the model is that double dissociations between regular and irregular inXection, resulting from stochastic processes should be extremely rare. However, they are particularly likely to occur when the researcher uses test batteries consisting of a small number of items. Given that cognitive neuropsychologists rarely provide details about the distribution of performance in a disordered population, it is concluded that a stochastic interpretation of double dissociations may have wider applicability than is normally supposed.

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