Figure 1.

(a) Dual task set-up: participants perform gripping actions with increasing/decreasing force (all experiments), or with sustained force (Experiment 5) while simultaneously evaluating whether a tone sequence accelerated or decelerated. A red bar provided a visual indicator of grip force. The upwards or downwards motion of two green triangular trackers provided the required rate of force increase or decrease (or indication of force error in Experiments 4 and 5). Participants had to adjust force throughout the trial to match the bar height to the tracker's motion (Increase/Decrease trials). (b) Both the action and the tone sequence took place in 3900 ms, after which participants responded whether the tone sequence appeared to accelerate or decelerate in a 2AFC scenario. (c) Inter-onset interval of each tone sequence (8 tones, 7 intervals). Δt ms indicates the difference in ms between the first and seventh interval. (d) Experiment 1. In the Action trials, grip force was directly mapped to the changes in bar height (Spatial Magnitude), i.e. increases (or decreases) in force were translated online into increases (or decreases) in bar height. In the No Action trials, the changes in bar height were externally controlled and perfectly matched the motion of the green trackers. (e) Experiment 1—PSI (points of subjective isochrony) in Δt ms for Increase/Decrease trials of the Action and No Action condition (error bars depict standard error). (Online version in colour.)