Origins of Dissociations in the English Past Tense: A Synthetic Brain Imaging Model

Gert Westermann,Samuel Jones

doi:10.3389/fpsyg.2021.688908

Abstract

Brain imaging studies of English past tense inflection have found dissociations between regular and irregular verbs, but no coherent picture has emerged to explain how these dissociations arise. Here we use synthetic brain imaging on a neural network model to provide a mechanistic account of the origins of such dissociations. The model suggests that dissociations between regional activation patterns in verb inflection emerge in an adult processing system that has been shaped through experience-dependent structural brain development. Although these dissociations appear to be between regular and irregular verbs, they arise in the model from a combination of statistical properties including frequency, relationships to other verbs, and phonological complexity, without a causal role for regularity or semantics. These results are consistent with the notion that all inflections are produced in a single associative mechanism. The model generates predictions about the patterning of active brain regions for different verbs that can be tested in future imaging studies.

Highlights

The English past tense has, over the past 35 years, taken center stage in the debate on the nature of language and cognitive processing
The main question around which this debate has revolved is whether there are separate processing mechanisms for regular and irregular verbs, or if they can be accounted for in a system that produces both regular and irregular forms through a single associative mechanism. This question is important because it has wider implications, for example, for the rule-like nature of grammar and for the question of whether behavioral dissociations imply that the language system has a modular architecture. These questions touch on the very nature of language and cognitive processing, and the English past tense has been called the “drosophila of language processing” (Pinker, 1994): a model system in which such questions can be studied in detail
The simulations described in this paper show how dissociations between brain activation patterns in inflection tasks can arise from a single associative mechanism together with experience-dependent structural development

Summary

Introduction

The English past tense has, over the past 35 years, taken center stage in the debate on the nature of language and cognitive processing. The main question around which this debate has revolved is whether there are separate processing mechanisms for regular and irregular verbs, or if they can be accounted for in a system that produces both regular and irregular forms through a single associative mechanism This question is important because it has wider implications, for example, for the rule-like nature of grammar (is rule-like behavior evidence for an underlying mental rule or can it be explained through associative processes?) and for the question of whether behavioral dissociations imply that the language system has a modular architecture. The dualmechanism or words-and-rules theory (e.g., Pinker, 1991, 1997, 1999; Marcus et al, 1995; Ullman et al, 1997; Clahsen, 1999; Pinker and Ullman, 2002; Ullman, 2004) holds that the processing

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