When using a tool, proximal action effects (e.g., the hand movement on a digitizer tablet) and distal action effects (e.g., the cursor movement on a display) often do not correspond to or are even in conflict with each other. In the experiments reported here, we examined the role of proximal and distal action effects in a closed loop task of sensorimotor control. Different gain factors perturbed the relation between hand movements on the digitizer tablet and cursor movements on a display. In the experiments, the covert hand movement was held constant, while the cursor amplitude on the display was shorter, equal, or longer, and vice versa in the other condition. When participants were asked to replicate the hand movement without visual feedback, hand amplitudes varied in accordance with the displayed amplitudes. Adding a second transformation (Experiment 1: 90°-rotation of visual feedback, Experiment 2: 180°-rotation of visual feedback) reduced these aftereffects only when the discrepancy between hand movement and displayed movement was obvious. In conclusion, distal action effects assimilated proximal action effects when the proprioceptive/tactile feedback showed a feature overlap with the visual feedback on the display.

Integration of discrepant visual and proprioceptive action effects puts high demands on the human information processing system. The present study aimed to examine the integration mechanisms for the motor (Exp. 1) and visual modality (Exp. 2). According to theories of common coding, we assumed that visual as well as proprioceptive information is represented within the same cognitive domain and is therefore likely to affect each other (multisensory cross talk). Thus, apart from the often-confirmed visual dominance in multisensory integration, we asked about intra- and intermodal recall of either proprioceptive or visual information and whether there were any differences between the motor and visual modality. In a replication paradigm, we perturbed the relation between hand movements and cursor movements. The task required the (intra- vs. intermodal) replication of an initially performed (seen) hand (cursor) movement in a subsequent motor (visual) replication phase. First, mechanisms of integration were found to be dependent on the output modality. Visual action effects interfered the motor modality, but proprioceptive action effects did not have any effects on the visual modality. Second, however, intermodal integration was more susceptible to interference, and this was found to be independent from the output modality. Third, for the motor modality, the locus of perturbation (perturbation of cursor amplitude or perturbation of hand amplitude) was irrelevant, but for the visual modality, perturbation of hand amplitudes reduced the cross talk. Tool use is one field of application of these kinds of results, since the optimized integration of conflicting action effects is a precondition for using tools successfully.

Modern tools in technological environments are often characterized by a spatial separation of hand actions (operating a remote control) and their intended action effects (displayed movements of an unmanned vehicle, a robot, or an avatar on a screen). Often non-corresponding proximal and distal movement effects put high demands on the human information processing system. The present study aimed to investigate how modern technological environments influence processes of planning and controlling actions. Participants performed ipsi- or contralateral movements in response to colored stimuli, while the stimulus location had to be ignored. They did not see the stimuli and hands directly, but received visual feedback (with retained or reversed spatial relations) on a projection screen in front of them. Visual feedback retaining spatial relations led to the usual Simon effect. However, visual feedback reversing spatial relations inverted the Simon effect in ipsilateral responses, and eliminated it in contralateral responses (Exp. 1). Impairing the proximal movement-effect loop so that proprioceptive/tactile information from the moving hand was no longer a reliable source for planning and controlling actions attenuated compatibility effects (Exp. 2). Moreover, distal action effects predominated action control even for opposing body-related effects. It seemed that action control of transformed movements depended on the reliability of proprioceptive/tactile and visual information. When the amount of feature overlap between proprioception and vision was low and proprioceptive (visual) information was no longer reliable, then distal (proximal) action effects stepped forward and became crucial in controlling transformed actions.

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