Attention for perception and action: task interference for action planning, but not for online control.

Human vision allows us both to perceive our surroundings (e.g., identify a cup) and to interact with them (e.g., reach for a cup). It is generally accepted that these functions are supported by a ventral system for conscious object identification and a dorsal system for unconscious control of action, but little research has addressed the extent to which these two systems can operate concurrently. We show that the identification of one object interferes with the planning of a pointing action to a second object, but does not interfere with the visually guided control required to complete the action. This lack of interference holds even for actions that must be modified in response to a dynamically changing scene. These findings support the proposal that the planning of action shares resources with conscious tasks of perception, but that the online control of already-initiated actions does not.