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Dwight Kravitz, Kadharbatcha Saleem, Chris Baker, Mortimer Mishkin; A new neural framework for visuospatial processing. Journal of Vision 2011;11(11):319. doi: 10.1167/11.11.923.
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© ARVO (1962-2015); The Authors (2016-present)
The division of cortical visual processing into functionally and anatomically distinct dorsal and ventral streams is a key component of theoretical frameworks guiding visual neuroscience. The characterization of the ventral stream as a ‘what’ pathway, contributing to the conscious representation of stimulus quality is relatively uncontroversial, but the nature of dorsal stream processing is less clear. Originally proposed as a ‘where’ pathway supporting spatial vision, more recent accounts have suggested it is a ‘how’ pathway, primarily supporting unconscious visually-guided action. Here, we synthesize anatomical, lesion, and functional evidence from human and monkey and propose that the dorsal stream actually gives rise to at least three distinct pathways: 1) parieto-prefrontal, 2) parieto-premotor, and 3) parieto-medial temporal, supporting eye movements and spatial working memory, visually-guided actions of the body (e.g. arm), and navigation, respectively. The anatomical and functional properties of the parieto-medial temporal pathway have not been well-characterized previously. The pathway courses medially, through the posterior cingulate and retrosplenial cortices, providing complex spatial information to the medial temporal lobe. The functional properties of the cortical areas along this pathway are consistent with a role in navigation, specifically the coordination of primarily egocentric parietal representations and allocentric medial temporal representations of space. We argue that the presence of these multiple pathways render previous characterizations of the dorsal stream as a ‘where’ or ‘how’ pathway incomplete. These labels fail to capture the breadth or complexity of spatial processing occurring within the dorsal stream or the diversity of its projections. We propose a new neural framework for visuospatial processing, in which the occipito-parietal circuit comprising the dorsal stream functions as a general spatial processor, supporting, through its projections, a diverse set of conscious and unconscious spatial processing across many areas of cortex.
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