Dissociations in processing past tense morphology: neuropathology and behavioral studies

Area of Science:

• Neuropsychology
• Linguistics
• Cognitive Neuroscience

Background:

• Past tense inflectional morphology (regular vs. irregular) dissociates in brain-damaged patients.
• This dissociation challenges single-system connectionist models and supports dual-system rule-based accounts.
• Neuropathology and behavioral data offer critical constraints for linguistic rule theories.

Purpose of the Study:

• To investigate the neural basis of regular and irregular past tense processing.
• To test competing computational models of past tense morphology using patient data.
• To correlate specific brain damage patterns with distinct processing deficits.

Main Methods:

• Tested nonfluent aphasic patients (left hemisphere damage) and semantic deficit patients (HSE, temporal lobe damage).
• Employed a large priming study to assess regular and irregular past tense priming.
• Utilized an elicitation task to evaluate irregular past tense performance.

Main Results:

• Nonfluent aphasic patients showed no regular past tense priming but significant irregular past tense priming.
• Control participants exhibited priming for both regular and irregular past tenses.
• HSE patients demonstrated significantly impaired irregular past tense performance in an elicitation task.

Conclusions:

• Behavioral and neuropathological findings suggest separable yet interdependent systems for regular and irregular past tense processing.
• Evidence supports distinct neural substrates for rule-based regular past tense and lexicon-based irregular past tense.
• The study provides strong constraints for computational models of language processing in the brain.