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The representation of perceived angular size in human primary visual cortex


Two objects that project the same visual angle on the retina can appear to occupy very different proportions of the visual field if they are perceived to be at different distances. What happens to the retinotopic map in primary visual cortex (V1) during the perception of these size illusions? Here we show, using functional magnetic resonance imaging (fMRI), that the retinotopic representation of an object changes in accordance with its perceived angular size. A distant object that appears to occupy a larger portion of the visual field activates a larger area in V1 than an object of equal angular size that is perceived to be closer and smaller. These results demonstrate that the retinal size of an object and the depth information in a scene are combined early in the human visual system.

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We thank S. He, F. Fang and P. Sinha for their comments and suggestions related to this manuscript. This work was supported by the US National Institutes of Health (F32 EY015342 to S.O.M. and RO1 EY-015261 to D.K.) and the National Geo-Spatial Intelligence Agency (HM1582-05-C-0003 to S.O.M.).

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Competing interests

The authors declare no competing financial interests.

Correspondence to Scott O Murray.

Supplementary information

  1. Supplementary Methods

    Additional behavioural measurements (PDF 60 kb)

  2. Supplementary Data

    Across subject comparison of behavioural and fMRI effect size (PDF 50 kb)

  3. Supplementary Note

    Binocular viewing and vergence eye movements (PDF 43 kb)

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Figure 1: Stimulus for the behavioral and fMRI experiments.
Figure 2: ROIs.
Figure 3: Imaging results.
Figure 4: Control experiments.