Complexity of sensorimotor transformations alters hand perception

Abstract

When using tools effects in body space and distant space often do not correspond or are even in conflict. The ideomotor principle holds that actors select, initiate and execute movements by activating the anticipatory codes of the movements’ sensory effects (Greenwald, 1970; James, 1890). These may be representations of body-related effects and/or representations of more distal effects. Previous studies have demonstrated that distant action effects dominate action control, while body-related effects are attenuated (e.g., Musseler and Sutter, 2009). In two experiments, participants performed closed-loop controlled movements on a covered digitizer tablet to control a cursor on a monitor. Different gains perturbed the relation between hand and cursor amplitude, so that the hand amplitude varied and the cursor amplitude remained constant, and vice versa. Within a block the location of amplitude perturbation randomly varied (low predictability) or not (high predictability). In Experiment 1 both trajectories of hand and cursor followed the same linear path, in Experiment 2 a linear hand trajectory produced a curved cursor trajectory on the monitor. When participants were asked to evaluate their hand movement, they were extremely uncertain about their trajectories. Both, predictability of amplitude perturbation and shape of cursor trajectory modulated the awareness of one’s own hand movements. We will discuss whether the low awareness of proximal action effects originates from an insufficient quality of the humans’ tactile and proprioceptive system or from an insufficient spatial reconstruction of this information in memory.