Rothkegel et al. 4 facilitator. While this mechanism was first discovered as an effect on a temporal scale, i.e., increased processing time at a previously attended stimulus for a specific time window, inhibition of return might carry over to spatial effects. In the case of spatial inhibition of return recently fixated positions are inhibited from being re-fixated shortly afterwards (Gilchrist & Harvey, 2000). Several studies were unable to report evidence for inhibition of return during scene viewing; quite the contrary, a facilitation of return saccades to currently fixated locations has been found (Smith & Henderson, 2009, 2011; Wilming et al., 2013). However, compared to statistical baseline model without memory based on inhibitory tagging, return saccades occur less often in experiments than expected (Bays & Hu- sain, 2012), when the density map of fixations and the distribution of angles between two subsequent saccades are reproduced. Therefore, there is at least weak support for a memory-producing mechanism during scene exploration. In agreement with this re- sult, we recently published a computational model of saccade generation in scene viewing that implemented both inhibitory tagging and dynamical attention mechanisms (Engbert, Trukenbrod, Barthelm´ e, & Wichmann, 2015). In model inhibitory tagging is combined with a dynamical activation map representing attention allocation, allowing the model to reproduce second-order statistics that include spatial correlation functions character- izing the clustering of fixations in addition to the first-order density of fixations. Thus, inhibitory tagging seems to be important to reproduce higher-order scanpath statistics (Engbert et al., 2015), despite the current lack of direct experimental support for inhibi- tion of return in scene viewing (Smith & Henderson, 2009, 2011; Luke et al., 2013). Saccadic momentum, another dynamical principle of saccade planning in scene viewing, describes the tendency to maintain the direction of the previous saccade for the upcoming