Within the dorsal stream account of visuomotor control, the role of visual awareness in guiding action remains controversial. We argue that addressing this question requires considering how action demands influence the processing of task-relevant visual information. Accordingly, we conducted two experiments in which participants performed a reaching movement to match their hand orientation to that of a briefly presented Gabor patch. Action biomechanical demands were modulated by varying the end-state comfort of hand rotations (i.e., amplitudes and directions). Experiment 1 tested clockwise rotations at small and large amplitudes, whereas Experiment 2 included both clockwise and counterclockwise rotations, each at two amplitudes. Visual awareness was manipulated by presenting Gabor orientations at the perceptual threshold, enabling comparisons of performance between aware and unaware trials. We analysed three parameters indexing distinct aspects of the action's underlying processes: hand rotation accuracy, rotation onset, and rotation smoothness. We found that visual information not consciously available could partially guide movement selection, but only when the movement was comfortable. Conversely, visual awareness was critical for uncomfortable movements, as performance dropped substantially when orientations were not consciously perceived. In addition, visual awareness produced different effects across phases of movement control: facilitated movement preparation (higher accuracy, earlier onset) but restrained execution (reduced smoothness). Our findings offer new insights into perception-action coupling and help clarify conflicting results in the literature concerning the role of visual awareness in motor control: whether visual awareness is necessary for motor control may depend on the biomechanical demands of the planned action.
Montani et al. (Tue,) studied this question.