Psychological Science 24(8) 1456–1465 © The Author(s) 2013 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0956797612473485 pss.sagepub.com Research Article Vision plays a significant role in everyday life, allowing people to perceive their surroundings and to guide their actions with respect to the objects in the environment. It has been proposed that the processing of incoming visual information takes place along two separate but interact- ing streams, each arising from primary visual cortex (Goodale & Milner, 1992). According to this proposal, the ventral stream—projecting to the inferotemporal cor- tex—is responsible for the detailed perceptual represen- tation of the objects in one’s surroundings, whereas the dorsal stream—projecting to posterior parietal areas— provides the metrics for flexible moment-to-moment pro- gramming and control of visually guided actions, such as reaching and grasping. Understanding one’s surroundings for the purposes of perception and action, however, requires more than sim- ply identifying and acting on objects in isolation. In reality, the visual world presents observers with cluttered and complex visual scenes that the visual system must parse and segment into discrete and meaningful objects. This process is clearly critical for perceiving objects (for relevant theories of perceptual parsing—particularly within the realm of numerical cognition—see, e.g., Allik & Tuulmets, 1991; Dehaene & Changeux, 1993), but is argu- ably just as important for successfully planning and exe- cuting visually guided actions directed at those objects. Historically, explanations of the two-visual-streams account have posited that the ventral stream plays the central role in scene parsing. It remains unclear, however, 473485PSS XX X 10.1177/0956797612473485Connectedness Fools the Eye but Not the HandMilne et al. research-article 2013 Corresponding Author: Melvyn A. Goodale, The Brain and Mind Institute, The University of Western Ontario, London, Ontario, Canada N6A 5B7 E-mail: mgoodale@uwo.ca Connecting the Dots: Object Connectedness Deceives Perception but Not Movement Planning Jennifer L. Milne 1,2 , Craig S. Chapman 3 , Jason P. Gallivan 4 , Daniel K. Wood 1,2 , Jody C. Culham 1,2,5 , and Melvyn A. Goodale 1,2,5 1 The Brain and Mind Institute, The University of Western Ontario; 2 Neuroscience Program, The University of Western Ontario; 3 Faculty of Physical Education and Recreation, The University of Alberta; 4 Department of Psychology, Centre for Neuroscience Studies, Queen’s University; and 5 Department of Psychology, The University of Western Ontario Abstract The perceptual system parses complex scenes into discrete objects. Parsing is also required for planning visually guided movements when more than one potential target is present. To examine whether visual perception and motor planning use the same or different parsing strategies, we used the connectedness illusion, in which observers typically report seeing fewer targets if pairs of targets are connected by short lines. We found that despite this illusion, when observers are asked to make speeded reaches toward targets in such displays, their reaches are unaffected by the presence of the connecting lines. Instead, their movement plans, as revealed by their movement trajectories, are influenced by the number of potential targets irrespective of whether connecting lines are present or not. This suggests that scene parsing for perception depends on mechanisms that are distinct from those that allow observers to plan rapid and efficient target-directed movements in situations with multiple potential targets. Keywords perception, action, scene parsing, reaching movements, movement planning, two visual streams, motor processes Received 7/18/12; Revision accepted 11/30/12