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Meaghan McManus, Jing Chen, Laurence Harris, Karl Gegenfurtner; The Neural Correlate Of Size Constancy Measured With SSVEP In Virtual Reality. Journal of Vision 2018;18(10):254. doi: https://doi.org/10.1167/18.10.254.
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When standing in a hallway and a person walks away from you, the retinal image of the person decreases, however, you still perceive them as being the same size. This is referred to as size constancy. If the retinal size were to remain constant as they get further we would perceive the person as getting larger. Previous findings from fMRI suggest that the perceived size of an object correlates with activation in V1 (Murray et al, 2006; Sperandio, et al., 2012). We explored how much the steady state visually evoked potential (SSVEP) would be modulated by the perceived size of an object relative to its retinal size. Participants viewed an environment presented in virtual reality (Oculus Rift) that had either strong distance cues (a hallway with stereo view), or limited distance cues (a featureless environment with monocular viewing). During a given trial participants saw an alternating black and white square flashing at 5hz at either 40cm or 80cm. The size of the near object increased and then decreased between 1.4 and 5.6cm over the course of 40 seconds. The sizes used for the far object were matched to the retinal sizes of the near object. At a fixed simulated distance, the amplitude of the SSVEP showed a strong dependence on the retinal size. At the same retinal size, the SSVEP amplitude was larger for the far distance compared to the near stimuli in the hallway environment. We conclude that the SSVEP over occipital cortex, presumable driven mainly by activity in V1, reflects the activation of size constancy mechanisms. ACKNOWLEDGEMENTS This study is supported by DFG IRTG 1901 and a research studentship from the NSERC CREATE program to MM.
Meeting abstract presented at VSS 2018
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