Mind over matter: A perceptual decision bias toward filled-in stimuli in the blind spot

Author Contributions 15 BE, JO and PK designed the study. BE and KH recorded and analyzed the data. BE, JO and PK 16 wrote and revised the manuscript. 17 18. CC-BY 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not. ABSTRACT 19 Modern theories of cognition place an emphasis on the (un)certainty of available 20 information. This raises the question whether we trust more external sampled information or 21 internal inference processes. The specific properties of visual processing around the blind spot 22 region allow us to address this. Although there are no photoreceptors corresponding to the 23 physiological blind spots, we experience visual content there as if it were veridical, when it is in 24 fact only " filled in " based on the surroundings. We asked subjects to choose between a stimulus 25 partially presented in the blind spot that elicits fill-in and another at the same eccentricity outside 26 of the blind spot. Subjects displayed a systematic bias toward the blind spot stimulus, where the 27 filled-in part could have actually concealed a non-target. Two control experiments confirmed this 28 finding and demonstrate that this is not an effect of eccentricity, but a property of the filling in 29 process. This intuitively puzzling effect finds a straightforward explanation within the context of 30 predictive coding. The filled-in signals are produced by the brain's generative model based on 31 spatial-context priors. In contrast to other locations, predictions at the blind spot cannot be 32 compared to feed-forwards inputs and therefore no error signal is generated. As a consequence, 33 the error measure for the inferred percepts reaches the lower bound and are estimated as more 34 reliable than actually seen contents. This experiment gives credibility to the interpretation of 35 bottom-up signals not as conveying independent information about the world, but information 36 relating to deviations of internal expectations. 37 38 SIGNIFICANCE 39 The common view treats visual processing as a hierarchy of increasingly refined 40 representations of external stimuli. In contrast, predictive coding interprets bottom-up relayed 41 information as error signals, indicating deviations from internal predictions. The validity of this 42 view is not easy to test. Here we utilize the phenomenon of fill-in in physiological blind spot region 43 to compare internally generated against veridical percepts. We demonstrate, that in the absence 44. …