# Effect of Stimulus Regularities on Eye Movement Characteristics
## 4 Discussion  
The study's results suggest that the attentional selection of relevant image characteristics varies with the experience obtained in experimental task performance. This change suggests an adaptive strategy of the observers that balances exploration and exploitation modes shown in the increased saccade number and the change in the saccade amplitude. They confirmed the usefulness of studying the eye movement characteristics to obtain information on the processes of attention, decision making, and memory. Statistical learning is typically considered a process involving implicit memory. Studying the role of unconscious memory in a search task in real-world scenes, [5] showed no effect of unconscious memory on the number of saccades. [PERSON] and [PERSON] [7] showed that eye movements were not necessary for implicit learning of spatial configurations, and keeping a stable fixation at the display center is beneficial for rapid learning of the spatial layout. Our results, however, show an increased number of eye movements in the sequential block of trials, but the gaze landings become more localized in the process of practice and learning. One distinctive feature of our study, compared to visual search studies, is that the relevant target or targets for successful task performance are not defined in advance. The participants have to determine which stimulus features to use for task performance. The large display size may facilitate an exploitative behavior with larger saccades in the initial stimulus blocks and more focused ones later on. The increase in fixation duration in the sequential blocks might be considered a switch from exploration to exploitation mode; however, the saccade number should decrease in this case. Our findings indicate that learning spatial regularities in the stimulus set leads to a transition from ambient to focal processing, a phenomenon commonly observed in single trials [9; 10]. Ambient processing is characterized by longer saccades and shorter fixations and is considered to be involved in processing spatial arrangements and extracting contextual information. In contrast, focal processing, which involves smaller saccades and longer fixations, reflects the processing of details and object identification. The increase in fixation duration and the decrease in saccade amplitude in the sequential blocks in our study may be considered as representing a more local focus of attention and a discrimination of the relevant from irrelevant stimulus features for task performance and their deeper exploration. The study results show a marginal effect of the stimuli on the fixation duration. The more pronounced change in this gaze parameter suggests a transition from ambient tofocal processing. The saccade amplitude change also suggests such a transition, as its magnitude decreases in the sequential epochs. Its independence from the rotation angle and the pattern position in a pair implies that the observers compare the relative positions of the chunks in the patterns. The unequal effects of the epoch on the different stimuli imply different learning rates. Based on the fixation duration and saccade amplitude outcomes, the data suggest more rapid learning for the different patterns. In the present study, we varied the co-occurrence of chunks in the patterns that formed a stimulus pair. Contrary to typical studies manipulating the co-occurrence of objects, in our task, the presence of the same chunks in different patterns makes stimulus discriminability more difficult due to the increased pattern similarity. The large number of unique stimulus pairs would not allow the use of memory for the combinations to discriminate the patterns as the same or different. However, the stimulus set contains statistical regularities that could facilitate the performance in the sequential epochs. The pattern A from each group appeared on the left side of the stimulus pairs in their original orientation.