content_image/323157.jpg
was displayed and the trial started anew with the initial fixation check. After successful initial fixation, participants were instructed to explore the scene freely for five seconds in all experiments. Experiments were run with the Matlab software (MATLAB, 2015) using the Psychophysics (Brainard, 1997; Pelli, 1997; Kleiner et al., 2007) and Eyelink (Cornelissen, Peters, & Palmer, 2002) toolboxes. 

## Data Analysis 

Data preprocessing and saccade detection . For saccade detection we applied a velocity- based algorithm (Engbert & Kliegl, 2003; Engbert & Mergenthaler, 2006). Saccades had a minimum amplitude of 0 . 5 ◦ and exceeded an average velocity during a trial by 6 (median- based) standard deviations for at least 6 data samples (12 ms). The epoch between two subsequent saccades was defined as a fixation. 

## Distance to Center over Time 

We computed the mean distance of the eye position to the image center DTC as a function of pre-trial fixation time ( T ). This was computed as follows 

<img src='content_image/323157.jpg'>

where x$_{jk}$ ( t ) indicates gaze position of participant j on image k at time t and x$_{center}$ indicates the image center. As a continuous-time measure, we computed the DTC of each sample of the eye-position time series. In this representation, a larger DTC indicates a less pronounced CFB and vice versa. For all experiments we visualized the mean DTC ( t ) to the image center for the entire 5 s observation window for each pre-trial fixation time. The observation window started at t = 0 with the disappearance of the fixation marker. 

