Observed manipulation enhances left fronto-parietal activations in the processing of unfamiliar tools.

Tools represent a special class of objects, as functional details of tools can afford certain actions. In addition, information gained via prior experience with tools can be accessed on a semantic level, providing a basis for meaningful object interactions. Conceptual representations of tools also encompass knowledge about tool manipulation which can be acquired via direct (active manipulation) or indirect (observation of others manipulating objects) motor experience. The present study aimed to explore the impact of observation of manipulation on the neural processing of previously unfamiliar, manipulable objects. Brain activity was assessed by means of functional magnetic resonance imaging while participants accomplished a visual matching task involving pictures of the novel objects before and after they received object-related training. Three training session in which subjects observed an experimenter manipulating one set of objects and visually explored another set of objects were used to make subjects familiar with the tools and to allow the formation of new tool representations. A control object set was not part of the training. Training-related brain activation increases were found for observed manipulation objects compared to not trained objects in a left-hemispheric network consisting of inferior frontal gyrus (iFG) pars opercularis and triangularis and supramarginal/angular gyrus. This illustrates that direct manipulation experience is not required to elicit tool-associated activation changes in the action system. While the iFG activation might indicate a close relationship between the areas involved in tool representation and those involved in observational knowledge acquisition, the parietal activation is discussed in terms of non-semantic effects of object affordances and hand-tool spatial relationships.

Observed manipulation of novel tools leads to mu rhythm suppression over sensory-motor cortices.

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.