Influence of initial fixation position 11 Mean horizontal distance from starting position . To analyse the potential dependence of the scanpath on the experimentally controlled starting position, we estimated the tem- poral evolution of the mean horizontal gaze position. In the first step, we computed the absolute value of the time-dependent horizontal distance to the starting position for each trial. The calculation was based on fixation positions and fixation durations obtained from data preprocessing. The estimated mean horizontal distance (MHD) from starting position was computed as where x$_{jk}$ ( t ) indicates horizontal gaze position at time step t (in milliseconds) for partici- pant j and image k . For each combination of image and participant, the starting position x$_{jk}$ (0) was either left or right (see Procedure). To obtain a comparable measurement for both starting positions, gaze position for right starters was mirrored on the vertical central X$_{MHD}$ ( t ) = 1 m · n n ∑ j =1 m ∑ k =1 ( x$_{jk}$ ( t ) − x$_{jk}$ (0)) , (1) Figure 3 . Schematic illustration of the experimental procedure. In the example, the first fixation check failed. After fixation check 2, exploration of the image started. Fixation Check 1 200 ms Fixation Check 2 1000 ms Masked Image if  Fixation Check 2 failed Repetition of Fixation Check 1 Repetition of Fixation  Check 2 Observation of the  image for 10 seconds