Abstract:

Embodied cognition theories assume that conceptual representations are essentially rooted in modal experiential information. However, abstract concepts that do not refer to entities with a direct sensorimotor connection have challenged these embodied theories. For example, it is still debated whether abstract verb meanings are represented in the sensorimotor system. After screening and analyzing previous studies, the involvement of the motor system in the representations of abstract verbs is believed to be modulated by motor features. Abstract verbs that are learned in conjunction with more motor experiences are more likely to be predominant in motor features and accordingly are grounded much more strongly in the motor system. The present study aimed to explore the causal role of motor features of abstract verbs in their representations in the motor system and provide an explanation for the variance of previous results.

Forty-four participants (6 males) were recruited for Experiment 1; one male participant withdrew for private reasons, and all of his data were removed from the analysis. Experiment 1 lasted four days. On Day 1 and Day 4, pre- and postlearning tests, respectively, were conducted; in these tests, participants were instructed to perform a lexical decision task first inside a 3.0 T Siemens Prisma magnetic resonance imaging (MRI) scanner. During scanning, 240 words (including 60 target novel words) were presented in a pseudorandomized sequence within an event-related design. Then, outside the scanner, the same behavioral task with 120 words (including 60 target novel words) was performed on computers with responses collected according to the action?sentence compatibility effect paradigm. On Days 2 and 3, participants spent approximately one hour each day learning and memorizing 60 target novel words and their interpretive abstract meanings, which were printed on cards. While learning, participants were asked to perform a specific hand movement toward or away from themselves as required, with the aim of successfully increasing the predominance of motor features associated with the target novel words. The neuroimaging data acquired during the fMRI tests were preprocessed and analyzed using SPM and DPABI. At the whole-brain level, a 2 × 2 ANOVA was performed. The two within-subject factors were the testing phase (pre- vs. postlearning) and word type (learning vs. nonlearning novel words). We found that for learning novel words, compared with the prelearning test, there were stronger activations in motion-related brain areas (such as the left precentral gyrus) during the postlearning test. Furthermore, the scores for motor features associated with learning novel words significantly predicted the degree of neural activation in the motor system (i.e., the right pre- and postcentral gyri, the left precentral gyrus, etc.) in the postlearning test.

Thirty participants from Experiment 1 participated in Experiment 2. They were instructed to learn 30 novel words selected from the above 60 target words in a similar way as in Experiment 1. After approximately 30 minutes of learning, the participants performed the lexical decision task while their arm’s electromyographic activities were recorded with a wireless electromyography (EMG) measurement module from BIOPAC. The results showed that processing learning novel words with increased motor features, compared with nonlearning novel words (i.e., the baseline), elicited increased EMG activities in the right extensor digitorum muscle.

In conclusion, the present study confirmed the causal role of motor features in the embodied representations (i.e., representations in the motor system) of abstract verbs. An increase in motor features makes the representations of abstract verbs more dependent on the motor system. Moreover, the processing of abstract verbs with sufficient motor features could elicit motor resonance in the peripheral motor system. These findings provide new evidence and important interpretations for embodied cognition theories.

Key words: motor features, abstract verbs, embodiment, task-fMRI, EMG