Abstract
Feedback within the oculomotor system improves visual processing at eye movement end points, also termed a visual grasp. We do not just view the world around us however, we also reach out and grab things with our hands. A growing body of literature suggests that visual processing in near-hand space is altered. The control systems for moving either the eyes or the hands rely on parallel networks of fronto-parietal regions, which have feedback connections to visual areas. Since the oculomotor system effects on visual processing occur through feedback, both through the motor plan and the motor efference copy, a parallel system where reaching and/or grasping motor-related activity also affects visual processing is likely. Areas in the posterior parietal cortex, for example, receive proprioceptive and visual information used to guide actions, as well as motor efference signals. This trio of information channels is all that would be necessary to produce spatial allocation of reach-related visual attention. We review evidence from behavioral and neurophysiological studies that support the hypothesis that feedback from the reaching and/or grasping motor control networks affects visual processing while noting ways in which it differs from that seen within the oculomotor system. We also suggest that object affordances may represent the neural mechanism through which certain object features are selected for preferential processing when stimuli are near the hand. Finally, we summarize the two effector-based feedback systems and discuss how having separate but parallel effector systems allows for efficient decoupling of eye and hand movements.
Highlights
Accumulating behavioral evidence has shown that visual processing is altered near the hand
We suggest that links between the visual system and the motor systems could drive enhanced processing of action-relevant object features, but that de-coupled eye and hand movements indicate the need for separate, effector-based selection mechanisms
Being able to separate the deployment of attention between effectors allows for the decoupling of actions
Summary
Accumulating behavioral evidence has shown that visual processing is altered near the hand. Speeded target detection and figure-ground assignment (Reed et al, 2006, 2010; Jackson et al, 2010), improvements in working memory (Tseng and Bridgeman, 2011), orientation processing (Craighero et al, 1999; Bekkering and Neggers, 2002; Hannus et al, 2005; Gutteling et al, 2011, 2013), target discrimination (Deubel et al, 1998), and in reaching and grasping precision (Brown et al, 2008), are just some of the effects seen when a reach places a hand near a visual stimulus. What remains a topic of debate is the mechanism by which these alterations in visual processing occur
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