fMRI reveals a lower visual field preference in dorsal visual stream regions during hand actions

Abstract

Humans have been shown to be more efficient when reaching or grasping stimuli in the lower visual field than in the upper visual field. This suggests that the dorsal “action” visual stream is biased towards processing information in the lower visual field. In line with this, several neurophysiological studies in the monkey have reported that neurons within the dorsal stream over-represent the lower visual field relative to the upper visual field. The present study used slow event-related functional magnetic resonance imaging (fMRI) to examine whether human brain areas implicated in action would show such visual field preferences. We asked ten participants to fixate one of four LEDs positioned in a square such that each LED was at 13° (visual angle) from a centrally presented object. Thus the objects could appear in the upper left, upper right, lower left or lower right visual field with respect to the fixation points. On some trials, participants reached to grasp the object with the right hand and on other trials they passively viewed the object. At the beginning of each trial, participants had to saccade to one of the fixation points and to maintain fixation there for the duration of the trial. By manipulating the position of the LEDs rather than the position of the objects, we ensured that the biomechanics of the movements did not differ across conditions. The superior parieto-occipital cortex and the anterior intraparietal area, brain areas implicated in the control of hand actions, showed significantly higher activation when participants grasped objects presented in the lower visual field than in the upper visual field. However, no visual field preferences were observed in these regions during passive viewing. These findings suggest that the neural responses within dorsal visual stream regions may reflect a lower visual field advantage specific to visually guided actions.

S. Rossit was funded by a fellowship [no. SFRH/BPD/65951/2009] from the Portuguese Foundation for Science and Technology (FCT) and Social European Fund (FSE).