Action Priority: Early Neurophysiological Interaction of Conceptual and Motor Representations

Abstract

Handling our everyday life, we often react manually to verbal requests or instruction, but the functional interrelations of motor control and language are not fully understood yet, especially their neurophysiological basis. Here, we investigated whether specific motor representations for grip types interact neurophysiologically with conceptual information, that is, when reading nouns. Participants performed lexical decisions and, for words, executed a grasp-and-lift task on objects of different sizes involving precision or power grips while the electroencephalogram was recorded. Nouns could denote objects that require either a precision or a power grip and could, thus, be (in)congruent with the performed grasp. In a control block, participants pointed at the objects instead of grasping them. The main result revealed an event-related potential (ERP) interaction of grip type and conceptual information which was not present for pointing. Incongruent compared to congruent conditions elicited an increased positivity (100-200 ms after noun onset). Grip type effects were obtained in response-locked analyses of the grasping ERPs (100-300 ms at left anterior electrodes). These findings attest that grip type and conceptual information are functionally related when planning a grasping action but such an interaction could not be detected for pointing. Generally, the results suggest that control of behaviour can be modulated by task demands; conceptual noun information (i.e., associated action knowledge) may gain processing priority if the task requires a complex motor response.

Fig 1. Setup.

The experimental setup, incl. the monitor indicating the boxed areas for the stimulus presentation, the three objects on pressure-sensitive buttons and a start button (closest to participant). All object positions could be reached comfortably with the extended arm. The object positions of the large and the small object were counter balanced.

Fig 2. Trial procedure.

Schematic representations of the trial procedure (similar for grasping and pointing). Participants had to grasp and briefly lift the (spatially) associated object for word stimuli using a precision or a power grip depending on the object size. Pseudo word constituted no-go trials in which the start button should not have been released. In the pointing block, grasping and lifting was replaced by pointing at the associated object (with an open hand).

Fig 3. Stimulus-locked ERP effect of (in)congruence in grasping.

Grand average ERPs for the effect of (in)congruence between conceptual noun information and grip types (congruent–blue; incongruent–red) and the difference wave (black). The incongruent was more positive than the congruent ERP between 100 and 200 ms. The topographical map (nasion at the top) shows the (posterior) scalp distribution of the effect (incongruent minus congruent). Note that the scale of the maps varies among figures to optimally present the distribution, not the size of the effect. Negativity is plotted upwards in this and all subsequent ERP plots.

Fig 4. Stimulus-locked ERP effect for noun information in grasping.

Grand average ERPs for conceptual noun information. Nouns referring to smaller object (requiring usually precision grips; red lines) showed a reduced N400 effect (500–650 ms) compared with nouns for larger objects (usually grasped with a power grip; blue lines). The difference wave is also shown (in black). The topographical map shows the central scalp distribution of the N400 effect (large minus small). Note, N (large); N (small): conceptual noun information referring to larger or smaller objects.

Fig 5. Stimulus-locked ERPs in pointing.

Grand average ERPs for the four conditions (noun concept × object size) in the control block. There was a broadly-distributed, long-lasting effect of object size beginning around 200 ms. The topographical map shows the central scalp distribution of the effect with a late right-hemispheric dominance (small objects minus large objects).

Fig 6. Response-locked ERPs in grasping.

Grand average ERPs for the four conditions (noun concept × grip type). The effect of grip type was significant in the left anterior electrodes between 100 and 300 ms.

Fig 7. Response-locked ERP effect for grip types in grasping.

Grand average ERPs for the grip types power (blue) and precision (red) and the difference wave (in black). Precision grips are associated with a more negative ERP than power grips in the left anterior ROI between 100 and 300 ms. The topographical map shows the left anterior scalp distribution of the grip type effect during movement execution.

Fig 8. Response-locked ERP effect for object size in pointing.

Grand average ERPs for small (red) and large objects (blue) together with the difference wave (in black). The effect of object size was broadly distributed and significant between 600 ms before and 400 ms after movement onset. The effect had a central maximum and did not interact with the ROI factors between -600 and -200 ms whereas it showed a right hemispheric dominance from -200 to 400 ms as indicated by the topographical maps (difference: small objects minus large objects).