The involvement of the brain's motor system in action-related language processing can lead to overt interference with simultaneous action execution. The aim of the current study was to find evidence for this behavioural interference effect and to investigate its neurophysiological correlates using oscillatory MEG analysis. Subjects performed a semantic decision task on single action verbs, describing actions executed with the hands or the feet, and abstract verbs. Right hand button press responses were given for concrete verbs only. Therefore, longer response latencies for hand compared to foot verbs should reflect interference. We found interference effects to depend on verb imageability: overall response latencies for hand verbs did not differ significantly from foot verbs. However, imageability interacted with effector: while response latencies to hand and foot verbs with low imageability were equally fast, those for highly imageable hand verbs were longer than for highly imageable foot verbs. The difference is reflected in motor-related MEG beta band power suppression, which was weaker for highly imageable hand verbs compared with highly imageable foot verbs. This provides a putative neuronal mechanism for language-motor interference where the involvement of cortical hand motor areas in hand verb processing interacts with the typical beta suppression seen before movements. We found that the facilitatory effect of higher imageability on action verb processing time is perturbed when verb and motor response relate to the same body part. Importantly, this effect is accompanied by neurophysiological effects in beta band oscillations. The attenuated power suppression around the time of movement, reflecting decreased cortical excitability, seems to result from motor simulation during action-related language processing. This is in line with embodied cognition theories.
Tool stimuli can be analyzed based on their affordance, that is, their visual structure hinting at possible interaction points. Additionally, familiar tools can initiate the retrieval of stored object-action associations, providing the basis for a meaningful object use. The mu rhythm within the electroencephalographic alpha band is associated with sensory-motor processing and was shown to be modulated during the sight of familiar tool stimuli, suggesting motor cortex activation based on either affordance processing or access to stored conceptual object-action associations. The current study aimed to investigate the impact of such associations, acquired by observation of manipulation, in a training study controlling for inherent object affordances and previous individual differences in object-related experience. Participants observed the manipulation of a set of novel tool objects and visually explored a second set of novel tools for which only functional information was provided. In contrast to non-trained objects, observed objects modulated the mu rhythm over left sensory-motor cortex within 200 ms after training. Additionally, both observed and visually explored objects modulated mu rhythm over right sensory-motor cortex in the same time window to some extent, with the effect being stronger for the latter. This result suggests that motor cortex activation in visual processing of tools can result from observation of tool manipulation. However, mu rhythm modulation, albeit with a different and less clear left-lateralized pattern, is also seen when the tools were only made visually familiar and when information was restricted to the tools function.
The grounded cognition framework proposes that sensorimotor brain areas, which are typically involved in perception and action, also play a role in linguistic processing. We assessed oscillatory modulation during visual presentation of single verbs and localized cortical motor regions by means of isometric contraction of hand and foot muscles. Analogously to oscillatory activation patterns accompanying voluntary movements, we expected a somatotopically distributed suppression of beta and alpha frequencies in the motor cortex during processing of body-related action verbs. Magnetoencephalographic data were collected during presentation of verbs that express actions performed using the hands (H) or feet (F). Verbs denoting no bodily movement (N) were used as a control. Between 150 and 500 msec after visual word onset, beta rhythms were suppressed in H and F in comparison with N in the left hemisphere. Similarly, alpha oscillations showed left-lateralized power suppression in the H-N contrast, although at a later stage. The cortical oscillatory activity that typically occurs during voluntary movements is therefore found to somatotopically accompany the processing of body-related verbs. The combination of a localizer task with the oscillatory investigation applied to verb reading as in the present study provides further methodological possibilities of tracking language processing in the brain.
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