Attentional limits and freedom in visually guided action.

Human vision supports both the conscious perception of objects (e.g., identifying a tea cup) and the control of visually guided action on objects (e.g., reaching for a tea cup). The distinction between these two functions is supported by neuroanatomy, neuropsychology, animal lesion studies, psychophysics and kinematics in healthy humans, as well as in overarching theories of the visual brain. Yet research on visual attention, which concerns limitations in processing information concurrently from multiple objects, has so far not fully exploited this functional distinction. Attention research has focused primarily on the conscious aspects of vision, to the relative neglect of the unconscious control of limb actions and whether we can perceive some objects concurrently while acting on others. Here we review research from our lab leading to the conclusions that (1) the finger is guided visually by an automatic pilot that uses different information from that of conscious vision, (2) conscious object identification interferes with concurrent planning of pointing to a second object, though not with the online control needed to complete the pointing action, (3) concurrent perception and action sometimes lead to benefits in motor performance, and (4) the automatic pilot is itself capacity limited in processing information concurrently from multiple locations. These findings help clarify the conditions under which interference-free multitasking is possible and point to new challenges for research on the attentional limits of unconscious visual processing.