*2.3. Trial Two: Hand and Handle Alignment in Picking up the Jug*

We grasp tools according to the intended use [23]. Thus, while we may grasp a hammer in different ways when we want to transport it, we will grasp it at the handle with the thumb towards the heavy part when we want to use it immediately to drive a nail into a wall. Although in apraxic patients a functional grasp does not guarantee the correct use of the tool [24], such a grasp serves as a strong attractor that increases the likelihood of executing the correct gesture [25]. Even for neurotypical participants, people are faster at performing a manual response to an object when they use the hand that is aligned with the handle of a manipulable object compared to its functional end [26]. This suggests that having some means of indicating which part of an object to grasp could be useful. The action could be cued by simple modifications to the handle, e.g., by using LEDs to draw the user's attention to the handle, or by having the handle move to indicate that it could be grasped.

Previous research has shown that people make faster responses, in reaction time tasks, when the orientation of an objects' handle matches the hand which is to be used for the response [27–32]. Trial 2 investigated the question of whether object animation can cue an action, and whether the appearance of the handle on the jug corresponded with the hand used. Relating these tasks to the literature on task sequencing and neurological damage, when patients are asked to demonstrate perform on everyday activities (such as using a coffee machine) they can have difficulty in following multi-step procedures [33]. For patients with right brain damage, the problems related to maintaining position in a sequence of steps (i.e., they could lose track of what they had done and what they might need to do next). For patients with left brain damage, the problems were related to aphasia and retrieval of functional knowledge. This showed that performance of task sequences has different levels of impairment to those observed in the use of single objects (which often relate to difficulties in inferring use from appearance).
