A neurocognitive perspective on language: The declarative/procedural model

Several models have been proposed to account for the neurocognitive basis of the mental lexicon (a repository of stored words) and the mental grammar (which captures the regularities of language). The declarative/procedural model argues that lexicon and language depend on two neural systems that are intensively studied in the context of memory: declarative and procedural memory. The declarative/procedural model links lexicon with the declarative system and with brain structures in temporal/temporoparietal regions. On the other hand, the model links grammar with the procedural system, and with structures in the basal ganglia and frontal cortex. The declarative/procedural model makes a set of specific predictions about the neurocognitive basis of lexicon and grammar, regarding their separability, computation, domain generality and localization. These predictions, which have been thoroughly tested in the context of the use of regular versus irregular word forms (walk–walked versus go–went), have been helpful in contrasting this model with other competing perspectives. Several lines of evidence support the declarative/procedural model over alternative views. This evidence has come from psycholinguistic studies, the analysis of developmental disorders of language, neurological cases, haemodynamic studies and neurophysiological observations. Collectively, the data show a double dissociation. On the one hand, there is a link between lexicon, associative-memory markers, the knowledge of facts and events, and temporal/temporoparietal regions. On the other, there is a link between grammar, motor and cognitive skills, and structures in the frontal lobe and the basal ganglia. The declarative/procedural model has several implications. First, studies of declarative and procedural memory should help to elucidate the neural bases of lexicon and grammar, and vice versa. Second, the model has clinical implications for people with developmental or adult-onset disorders of grammar, as they might recover through the memorization of complex forms using the declarative system. Last, the existence of systems that subserve language in humans and are homologous to systems present in other animals has implications for the evolution of language.