Action relevance in linguistic context drives word-induced motor activity

Abstract

Many neurocognitive studies on the role of motor structures in action-language processing have implicitly adopted a "dictionary-like" framework within which lexical meaning is constructed on the basis of an invariant set of semantic features. The debate has thus been centered on the question of whether motor activation is an integral part of the lexical semantics (embodied theories) or the result of a post-lexical construction of a situation model (disembodied theories). However, research in psycholinguistics show that lexical semantic processing and context-dependent meaning construction are narrowly integrated. An understanding of the role of motor structures in action-language processing might thus be better achieved by focusing on the linguistic contexts under which such structures are recruited. Here, we therefore analyzed online modulations of grip force while subjects listened to target words embedded in different linguistic contexts. When the target word was a hand action verb and when the sentence focused on that action (John signs the contract) an early increase of grip force was observed. No comparable increase was detected when the same word occurred in a context that shifted the focus toward the agent's mental state (John wants to sign the contract). There mere presence of an action word is thus not sufficient to trigger motor activation. Moreover, when the linguistic context set up a strong expectation for a hand action, a grip force increase was observed even when the tested word was a pseudo-verb. The presence of a known action word is thus not required to trigger motor activation. Importantly, however, the same linguistic contexts that sufficed to trigger motor activation with pseudo-verbs failed to trigger motor activation when the target words were verbs with no motor action reference. Context is thus not by itself sufficient to supersede an "incompatible" word meaning. We argue that motor structure activation is part of a dynamic process that integrates the lexical meaning potential of a term and the context in the online construction of a situation model, which is a crucial process for fluent and efficient online language comprehension.

Keywords: conceptual flexibility; context-dependency; embodied language; lexical semantics; situation models.

Figure 1

Experimental material and setting. (A) A standalone 6-axis load cell of 68 g was used (ATI Industrial Automation, USA). (B) The three main forces were recorded: Fx, Fy, and Fz as the longitudinal, radial and compression forces, respectively. (C) Participants hold the grip-force sensor in a precision grip with their right hand. Bottom panel: participants wore headphones and were comfortably seated behind a desk on which a pad was placed. They were asked to rest their arms on the pad, holding the sensor.

Figure 2

Modulation of the grip-force amplitude as a function of time after target onset in Experiment 1 (Volition). (A–C) displays individual data for the three conditions (the bold lines represent the means and standard deviations) and (D) compares data of the three conditions averaged over all participants. In (D) we also show the standard error of the mean (s.e.m.) around the mean value across the subjects (shaded regions). For the action-in-focus condition a significant increase in the grip force was observed soon after target words presentations and it is maintained over the three intervals. This enhanced grip-force is significantly different from the volition condition in the two last windows and from the nouns conditions in the last window. The color of the asterisk refers to the color of the condition that is compared.

Figure 3

Modulation of the grip-force amplitude as a function of time after target onset in Experiment 2 (Pseudo-verbs). (A–D) Displays individual data for the four conditions (the bold lines represent the means and standard deviations) and (E) compares data of the four conditions averaged over all participants. In (E) we also show the standard error of the mean (s.e.m.) around the mean value across the subjects (shaded regions). For the action-action condition and the action-pseudo-verb condition, a significant increase in the grip force was early observed, and maintained until the last interval. This enhanced grip-force is significantly different from action-non-action condition in the two first intervals. The color of the asterisk refers to the color of the condition that is compared.