Neurocognitive correlates of category ambiguous verb processing: The single versus dual lexical entry hypotheses

Abstract

Word-class ambiguous words engender greater processing time and fMRI (BOLD signal) activation than unambiguous ones. Theoretical accounts of this phenomenon suggest that words with multiple meanings (1) are associated with multiple lexical entries and thus require greater selection demands, or (2) undergo computationally expensive grammatical processes that convert words from one word-class to another. Using an fMRI grammaticality judgment task, we tested these accounts by examining word-class ambiguous polysemic (e.g., brush) and homonymic (e.g., bear) verbs, and unambiguous verbs (e.g., bake). Results showed that ambiguous verbs evoked longer response times and greater neural activation in the left inferior frontal and parietal gyri. However, homonymic verbs also showed increased left inferior frontal and temporal neural activations compared to polysemic verbs. This indicates that rather than having multiple lexical representations like homonyms, polysemic verbs may share a core representation with their noun counterparts.

Keywords: Categorical ambiguity; Conversion/zero-morphology; Semantic control; Word-class; fMRI.

Copyright © 2019 Elsevier Inc. All rights reserved.

Figures

Fig. 1.

Schematic of verb (left) and letter (right) trials in the grammaticality judgment task.

Fig. 2.

Mean response time across the three verb conditions (right) (***p < .001, **p < .01). Bars indicate ± 1 standard error of the mean.

Fig. 3.

Activation maps showing activation for the lexical effect: verbs over letters in the left inferior frontal lobe (red), and letters over verbs in the right parietal and occipital areas (blue). The presented map is thresholded atp < .05, FWER corrected using cluster-extent based thresholding (k > 65) with primary threshold ofp < .001.

Fig. 4.

Activation maps showing activation for: (A) the ambiguity effect (ambiguous over unambiguous verbs) in the left frontal and parietal areas and the time course of the mean % BOLD signal change in these areas for the three verb conditions, (B) the verb category effect (homonymic over unambiguous and polysemic verbs) in the left inferior frontal and temporal areas. The presented maps are thresholded atp < .05 FWER corrected, using cluster-extent based thresholding (k > 70) with primary threshold ofp < .001.