  The key issue in considering the bearing of Bayesianism on the Nativist-Empiricist controversy is the  priors.[29] Where do they come from? If we are talking about simple, repeatable events like coin flips, the priors are a matter of well-defined relative frequencies given by probability theory. But the prior in the concave-convex case (which was chosen to highlight this point) seems to involve domain-specific facts about light and shadow, and their relation to the shape of objects. Scholl 2005 argues that the priors here are innate, and many scientists studying visual perception would agree. We don’t learn from experience that the objects in our perceptual world will typically have overhead illumination. Rather, this is one of the ‘factory settings’ of the visual system. As Kersten (2004) puts it (speaking more generally): ‘the priors are in the genes’. Ullman (1979) argues that the same may well hold for the general constraints relating the rigidity of objects to facts about motion. The view that the illumination constraint is innate is also supported by the fact that chickens reared in an abnormal illuminated-from-below environment still react as we do to stimuli (a) and (b) (Hershberger 1970). So we have evidence that this prior can be innate.