Fig. 1

Experimental design

a) Illustration of the KINARM Exoskeleton, which is a robot which gathers kinematic data from the upper limbs during task performance.

b) Experimental stages. Stage 1 involves Practise and Normalisation (of upper limb motor ability – see 1d), while Stage 2 involves the Confidence experiment (see 1e).

c) Illustration of the workspace and of the limb configuration. Participants were asked to make 10cm reaching movements from a start target to a peripheral target. Both were aligned so that the start target was at the midpoint of each limb’s workspace (90° elbow flexion and 30° shoulder flexion).

d) Illustration of the Normalisation procedure. During the second part of Stage 2 participants made 20 reaching movements but without visual feedback of both the cursor and the peripheral target once they exited the start target. Reaching ability was normalise using the following procedure: (1) Determine reaching end points of each trial, (2) build a confidence ellipse with 99.9% confidence interval around the scatter, (3) Obtain the target that has ~100% success likelihood (T100; i.e., participants would have hit this target in almost every trial), (4) Create targets based on T100 with increasing difficulty level (T65 – T5).

e) Illustration of a trial during the Confidence Experiment. Participants were presented with one of the 5 targets determined during Normalisation. (1) Prior to reaching participants were asked to rate how confident they were in hitting the target (Confidence Rating 1 – CR1), (2) After logging the verbal report participants aimed for the target without visual feedback of both the cursor and target, (3) After 2000ms participants were asked to rate how confident they were that they hit the target (Confidence Rating 2 – CR2), (4) After logging the verbal report, visual feedback was turned on again and participants could start a new trial by moving the cursor into the start target.