Grip force is part of the semantic representation of manual action verbs

Abstract

Motor actions and action verbs activate similar cortical brain regions. A functional interference can be taken as evidence that there is a parallel treatment of these two types of information and would argue for the biological grounding of language in action. A novel approach examining the relationship between language and grip force is presented. With eyes closed and arm extended, subjects listened to words relating (verbs) or not relating (nouns) to a manual action while holding a cylinder with an integrated force sensor. There was a change in grip force when subjects heard verbs that related to manual action. Grip force increased from about 100 ms following the verb presentation, peaked at 380 ms and fell abruptly after 400 ms, signalling a possible inhibition of the motor simulation evoked by these words. These observations reveal the intimate relationship that exists between language and grasp and show that it is possible to elucidate online new aspects of sensorimotor interaction.

Figure 1. The experimental paradigm.

Participants wore headphones and were seated on a chair facing a table. The instrumented cylinder was placed at a distance of 53.5 cm from their chest.

Figure 2. Functioning of the instrumented cylinder.

A. The apparatus is designed to measure the orientation (θ) and vertical location (x) of the applied force (P) by either the index or thumb while exerting a grip force. These parameters are computed from outputs of a F/T sensor (with axes X, Y and Z) embedded in the two half-cylinders using two T-adaptors. B. The participants were asked to lift the cylinder with the thumb and index fingers of the right hand and hold it at about 5 cm above the table.

Figure 3. Normalized grip force amplitude.

Grand average of normalized grip force amplitude of verbs and nouns –when they are targets– between the onset of a stimulus word until the end of the longest word duration. Compared to the nouns, the presence of verbs induced an early change in the signal following word onset. The shaded portion of the graph, starting at 260 ms and ending at 430 ms, shows the area where the two curves are significantly different (p<0.05).