Humans are experts at designing and utilizing unique tools to accomplish various tasks, like wielding an axe to chop wood. Humans are also capable of using different tools to accomplish opposing motor tasks simultaneously. While a lot is known about motor adaptation with changed visual feedback of the hand, we rarely consider how adaptation may differ in novel situations requiring pairs of tools with similar or different movement patterns. Here we test whether having two tools that require different movements to accomplish a similar goal would serve as sufficient cues for dual tool-use adaptation.
We ran an immersive virtual reality experiment where participants used one of two sets of tools; a motor incongruent pair, comprised of a paddle (forward motion) and a slingshot (backward motion), or a motor congruent pair, where participants used a paddle and a curling tool (both requiring forward motions). Participants swapped between tools every 8 trials. After a familiarization phase, we added visually opposite perturbations to the ball after it was launched from each tool (30o clockwise or counterclockwise rotation).
We found that the motor incongruent and motor congruent groups had reduced angular error in the exposure phase, suggesting that participants were able to form distinct motor memories for both pairs of tools. However, the reduction of angular error in the motor incongruent group was 27% larger than that of the congruent group, which supports the notion that separate motor memories are more reliant on the movement profile of a perturbation than any associative visual cues.