September 2018
Volume 18, Issue 10
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2018
Any double representation of the fovea? If there are ipsilateral connection from the eye to the LGN, why is there no cortical representation?
Author Affiliations
  • Mark Schira
    School of Psychology, University of Wollongong, Australia
Journal of Vision September 2018, Vol.18, 576. doi:10.1167/18.10.576
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      Mark Schira; Any double representation of the fovea? If there are ipsilateral connection from the eye to the LGN, why is there no cortical representation?. Journal of Vision 2018;18(10):576. doi: 10.1167/18.10.576.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

The debate about a double representation of the fovea in human visual cortex is still ongoing (Jordan et al. 2014). Ipsilateral connections from the retina to the LGN and hence visual cortex exist, they are reasonably well described (Stone 1973, Bunt & Minkler 1977, Fukuda et al. 1989) and some ipsilateral connections are found for the central 0.5 degrees in the fovea (1 degree in diameter). The retinotopic representation of the foveal confluence in human visual cortex, specifically the central 0.5 degree, is substantial with more that 2000 mm2 for V1, V2 and V3 alone (Schira et al. 2009). However, this area is representing the contralateral visual field, a representation of the ipsilateral visual field cannot be seen in the vicinity. It would have to be very small (less than 10mm2) to be undetectable. Reanalysing the data by Bunt & Minckler and Fukuda et al., only a very small count between 110 and 130 cells was estimated. When contemplating the impact for conscious perception three important facts need to be acknowledged: Firstly, while the ipsilateral overlap is relatively large in the periphery (up to 15 degree), close to the fovea it is smallest, either completely absent or less than 0.5 degree. Secondly, there are a substantial number of transcallosal fibers along the representation of the vertical meridian at the boundary of V1 and V2, especially in the foveal confluence (Zeki et al. 1969, Van Essen et al. 1986) suggesting a double representation would be superfluous. Finally, macular sparing, a popular argument for suggesting a substantial double representation, clearly cannot be well explained by an ipsilateral representation of the visual field. Quite obviously so, as many patients with hemianopia have no macular sparing whatsoever (Reinhard & Trauzettel-Klosinski, 2003), an observation that is irreconcilable with a significant ipsilateral representation.

Meeting abstract presented at VSS 2018

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