Humans are more efficient when performing actions towards objects presented in the lower visual field (VF) than in the upper VF. The present study used slow event-related functional magnetic resonance imaging (fMRI) to examine whether human brain areas implicated in action would show such VF preferences. Participants were asked to fixate one of four different positions allowing objects to be presented in the upper left, upper right, lower left or lower right VF. In some trials they reached to grasp the object with the right hand while in others they passively viewed the object. Crucially, by manipulating the fixation position, rather than the position of the objects, the biomechanics of the movements did not differ across conditions. The superior parieto-occipital cortex (SPOC) and the left precuneus, brain areas implicated in the control of reaching, were significantly more activated when participants grasped objects presented in the lower VF relative to the upper VF. Importantly, no such VF preferences were observed in these regions during passive viewing. This finding fits well with evidence from the macaque neurophysiology that neurons within visuomotor regions over-represent the lower VF relative to the upper VF and indicate that the neural responses within these regions may reflect a functional lower VF advantage during visually-guided actions.
Keywords: Brain; Grasping; Parietal lobe; Vision; Visuomotor control.
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