Table 1.

Description of tasks and hypotheses

Task	Description
Real tool use	The individual actually uses a toola (e.g. hammer) with an object a (e.g. nail). In some cases, several tools or objects are presented, and the individual must select the correct one to actually perform the tool-use action expected (i.e. tool selection).
Familiar tool use	Only familiar tools are presented. Familiar tool use differs from ‘activity of daily living’70 in which the individual has to perform a sequence of familiar tool-use actions. Note also that in familiar tool-use tasks, the individual has to use tool-object pairs. By contrast, activity-of-daily-living tasks involve multiple tools and objects, implying the selection of the tools and objects that are appropriate to perform the appropriate sequence of actions.
Novel tool use	The task can consist in using familiar tools in a non-conventional way (e.g. driving a screw with a knife) or in selecting, making and/or using novel tools to solve mechanical problems.
Single tool use	The individual grasps a tool presented in isolation and shows how to use it.
Pantomime of tool use	The individual demonstrates the use of a tool presented in isolation without holding it in hand.
Verbal modality	The name of the tool or a verbal description of the corresponding tool-use action is provided.
Visual modality	A picture of a tool or the real tool itself is shown.
Imitation modality	The examiner performs the tool-use action without holding the tool in hand.
Hypothesis
Gesture engram	This hypothesis is grounded on the idea that all tool-use situations—including pantomime—critically require specific motor programs specifying the features of the movements to be performed to use a specific tool. These motor programmes have been labelled with different terms, such as visuo-kinesthetic motor engram,20 action lexicon,214 gesture engram112 or manipulation knowledge.135 We will hereafter use the generic term motor engram and, as a result, will call this perspective the gesture-engram hypothesis.
Communicative	This hypothesis highlights the important—if not exclusive—role of communicative/language skills in pantomime.
Mixed	This non-exclusive hypothesis suggests that both gesture engrams and communicative skills contribute to the production of pantomime. In other words, gesture engrams and communicative skills are complementary.
Technical reasoning	This hypothesis assumes that all tool-use situations—including pantomime—require reasoning about the physical properties of tools and objects to generate a mental simulation of the mechanical action appropriate to perform the task. Then, this mental simulation orients the selection, planning and online control of the appropriate motor actions within the motor-control system. This hypothesis does not exclude that additional cognitive processes can be at play in pantomime because of the absence of specific information.

^aThe term tool will be hereafter used for the implement that performs an action (e.g. hammer) and the term object for the recipient of the action (e.g. nail).