Krügel Rothkegel Engbert_The presence and absence of the saccadic range effect explained

In an influential theoretical model, human sensorimotor control is achieved by a Bayesian decision process, which combines noisy sensory information and learned prior knowledge (Wolpert & Landy, 2012). A ubiquitous signature of prior knowledge and Bayesian integration in human perception and motor behavior is the frequently observed bias towards an average stimulus magnitude (i.e., a central-tendency bias, range effect, regression-to-the-mean effect). However, in the domain of eye movements there is a recent controversy about the fundamental existence of a range effect in the saccadic system (Gillen, Weiler, & Heath, 2013; Nuthmann, Vitu, Engbert, & Kliegl, 2016). Here we argue that the problem of the existence of a range effect is linked to the availability of prior knowledge for saccade control. We present results from two prosaccade experiments which both employ an informative prior structure (i.e., a non-uniform Gaussian distribution of saccade target distances). Our results demonstrate the validity of Bayesian integration in saccade control which generates a range effect in saccades. According to Bayesian integration principles, the saccadic range effect depends on the availability of prior knowledge and varies in size as a function of the reliability of the prior and the sensory likelihood.