PURPOSE: Using functional MRI and a virtual three-dimensional paradigm, we aimed at examining whether the parieto-occipital junction (POJ) acts as an interface for the integration and processing of information between the dorsal and ventral streams in the near and far space processing.
METHODS: Each participant completed two runs: a run for ‘match’ stimuli (visual angles of stimuli were matched in the near and far spaces, and a run for ‘natural’ stimuli (visual angles of stimuli were same in the near and far spaces. For each of ‘match’ and ‘natural’ runs, participants were asked to perform three types of tasks on an identical stimulus set: allocentric (ALLO) task, egocentric (EGO) task and high-level baseline (HLB) task. Therefore, the experimental design was a two (stimulus size: ‘match’ vs. ‘natural’) by two (spatial domains: Near vs. Far) by three (tasks: ALLO, EGO, and HLB) blocked design. Virtual reality three-dimensional near and far space was defined by manipulating binocular disparity, with -68.76 arcmin crossed disparity for near space and +68.76 arcmin uncrossed disparity for near space.
RESULTS: The POJ and bilateral superior occipital gyrus (SOG) showed relative increased activity when responded to targets presented in the near space than in the far space, which was independent of the retinotopic and perceived sizes of target. Furthermore, the POJ showed the enhanced functional connectivity with both the dorsal and ventral streams during the far space processing irrespective of target sizes. In contrast, the bilateral SOG showed the enhanced functional connectivity only with the ventral stream if retinotopic sizes of targets in the near and far spaces were matched.
CONCLUSIONS: The POJ acts as a neural interface between the dorsal and ventral streams in disparity-defined near space and far space processing.