# Effect of Stimulus Regularities on Eye Movement Characteristics
## 1 Introduction
Spatial regularities in a visual scene are related to the eye landings at relevant areas of interest in the visual scenes, whereas temporal regularities produce anticipatory eye movements reflecting the prediction of future stimulus positions based on the acquired knowledge from the stimulation. We studied the potential changes in four characteristics of eye movements: fixation duration, saccade number, gaze number, and saccade amplitude. The fixation duration is related to the depth and speed of the information processing. Short fixations (50-150 msec) [10] are considered ambient, reflecting unconscious processing. Focal fixations [10] are supposed to reflect conscious processing, focusing on details and object identification. The focal/ambient mode of image processing is also associated with changes in saccade amplitude. Short fixations are usually combined with large saccades, while the opposite is true for long fixations, reflecting the focal mode of processing. [PERSON] and co-authors [11] showed a transition from an ambient mode of processing (short fixations and large saccade amplitudes) to a focal processing mode (long fixations and short saccades) during a single trial. In our study, conversely, we aim to explore the changes in the dynamics of eye movements during the learning process. We hypothesize that the participants will use the ambient mode of processing in the initial stages of the study to obtain maximal information about the spatial layout of the images. In contrast, when they acquire enough knowledge of the stimulus structure, they will switch to the focal mode with longer fixations, indicating deeper cognitive processes and a longer time for analyzing and interpreting the stimulus information. Hence, we expect the fixation duration to increase and the saccade amplitude to decrease in the learning and practice process. Alternatively, the fixation duration might decrease. Short fixations are seen, for example, for expert readers (e.g., [12; 13]). Practice is shown to reduce the location and identity uncertainty in visual search tasks, thereby reducing fixation duration [14; 15]. Moreover, the participants were under time pressure (we limited the stimulus presentation to 3 s), a condition also known to reduce fixation duration [16]. Hence, in our experimental conditions, the repetition frequency of the patterns and the co-occurrence of visual chunks may allow participants to gain familiarity with the pattern combinations, adopting strategies that enable them to process relevant stimulus information more rapidly. Such an experimental outcome aligns with findings from previous studies, which suggest that expertise and time constraints can lead to shorter fixation durations as participants become more efficient in their visual search strategies. If a transition from an ambient to a focal mode of processing occurs during the sequential trials, the saccade amplitude would be expected to decrease in the sequential blocks due to the correlation between the fixation duration and saccade amplitude. Moreover, it has been shown that the repetitive presentation of the patterns leads to a smaller attentional span and, thus, smaller saccade amplitudes [17; 18]. The saccade number is tightly related to the number of fixations. It is supposed to reflect the efficiency of information search behavior, the complexity of the inference processes, and information acquisition. We expect that the saccade number will decrease in the sequential blocks of the trials due to the knowledge of the task and the improved discrimination of relevant from irrelevant stimulus information. However, in a study testing repetition effects in visual search [5], the authors related the improvement in search performance to unconscious memory. They showed that the unconscious memory did not affect the saccade number but made each saccade more efficient. The gaze number reflects the number of regions of interest the participants select to perform the task.