September 2015
Volume 15, Issue 12
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2015
Metamers of the ventral stream revisited
Author Affiliations
  • Thomas Wallis
    Neural Information Processing Group, Faculty of Science, University of Tübingen, Germany Werner Reichardt Centre for Integrative Neuroscience and Institute for Theoretical Physics, University of Tübingen, Germany
  • Matthias Bethge
    Werner Reichardt Centre for Integrative Neuroscience and Institute for Theoretical Physics, University of Tübingen, Germany Bernstein Center for Computational Neuroscience Tübingen, Germany
  • Felix Wichmann
    Neural Information Processing Group, Faculty of Science, University of Tübingen, Germany Bernstein Center for Computational Neuroscience Tübingen, Germany
Journal of Vision September 2015, Vol.15, 554. doi:10.1167/15.12.554
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      Thomas Wallis, Matthias Bethge, Felix Wichmann; Metamers of the ventral stream revisited. Journal of Vision 2015;15(12):554. doi: 10.1167/15.12.554.

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

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Abstract

Peripheral vision has been characterised as a lossy representation: information present in the periphery is discarded to a greater degree than in the fovea. What information is lost and what is retained? Freeman and Simoncelli (2011) recently revived the concept of metamers (physically different stimuli that look the same) as a way to test this question. Metamerism is a useful criterion, but several details must be refined. First, their paper assessed metamerism using a task with a significant working memory component (ABX). We use a purely spatial discrimination task to probe perceptual encoding. Second, a strong test of any hypothesised representation is to what extent it is metameric for a real scene. Several subsequent studies have misunderstood this to be the result of the paper. Freeman and Simoncelli instead only compared synthetic stimuli to each other. Pairs of stimuli were synthesised from natural images such that they were physically different but equal under the model representation. The experiment then assessed the scaling factor (spatial pooling region as a function of retinal eccentricity) required to make these two synthesised images indiscriminable from one another, finding that these scaling factors approximated V2 receptive field sizes. We find that a smaller scale factor than V2 neurons is required to make the synthesised images metameric for natural scenes (which are also equal under the model). We further show that this varies over images and is modified by including the spatial context of the target patches. While this particular model therefore fails to capture some perceptually relevant information, we believe that testing specific models against the criteria that they should discard as much information as possible while remaining metameric is a useful way to understand perceptual representations psychophysically.

Meeting abstract presented at VSS 2015

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