The influence of action on reachability and distance perception

Grade, Stéphane [UCL] Pesenti, Mauro [UCL] Edwards, Martin [UCL]

In the current literature, it is known that action, reachability spatial perception and magnitude spatial perception all rely on parietal lobe processes. However, it remains unclear what differences exist between the different behaviours, and moreover, whether there is a common underlying cognitive process underlying the behaviours. To investigate this, we measured spatial perception using reachability judgement and distance magnitude estimation tasks. The reachability judgement task measured judgements of whether a stimulus was within reach, while the distance magnitude estimation task measured the estimated distance between the participant and the stimulus. Both measures used the same stimuli and they were presented at different spatial locations on the participant’s sagittal axis, with half of the stimuli being presented within reach space and half outside of reach space (i.e., peri- and extra-personal spaces). Previous research has shown that reachability judgements are slower and show increased error for objects located at the boundary between peri- and extra-personal spaces. Therefore, if action processes underlie reachability and distance magnitude tasks, then objects presented at the boundary of the spaces may also moderate distance magnitude responses. A further manipulation was to have participants make concurrent actions during the two tasks. We predicted that if action processes are needed for both the reachability and distance magnitude tasks, then performing an action at the same time might perturbate the dependent variables. The results are discussed in terms of whether the relationships between action, reachability spatial perception and magnitude spatial perception rely on the same underlying cognitive processes.