# Effect of Stimulus Regularities on Eye Movement Characteristics
## 3 Results
### Saccade Amplitude  
The saccade amplitude would depend on the distinctive features of the patterns that allow for better discrimination. Thus, comparing the chunks in a pattern and between the patterns in the stimulus would be needed. Figure 11 shows the distributions of the saccade amplitudes in the sequential epochs. It clearly shows their bimodality. The two modes of these distributions occur because of the eye movements inside the patterns in the stimulus and between them.  
Figure 11: Distribution of the saccade amplitude in the sequential epochs (1–6) of the experiment.  
Figure 10: Predicted number of gazes for different pattern combinations and epochs.  
We tested whether the saccade amplitude varies with the rotation angle of the patterns. Analyzing the overall effect of the rotation angle for the whole set of stimuli is not very meaningful since the rotation angle has different effects for the different stimuli, changing the relative distances between the chunks in the two patterns in a stimulus. The effect of the rotation angle might be shown as a difference between the three stimuli in a group that contains the same patterns in the same position, differing only by the rotation angle. Each group contains eight such triples, with three comparisons in each. The results show that the 90% credible intervals of the amplitudes do not overlap for several members of each group (Figure 12A-C).  
The comparison of the saccade amplitude shows that it is significantly larger for the same patterns than for the different patterns. The evidence strongly supports the alternative hypothesis of there being a larger saccade amplitude for the same patterns compared to the different patterns against the null hypothesis of no difference (estimate = 0.17; [0.10-0.25], evidence ratio (EF) = for Group 1, estimate = 0.10 [0.03-0.18] for Group 2, and 0.16 [0.08-0.24] for Group 3 (the values in brackets are the 95% credible intervals)).  
The highest density interval (HDI) for the epochs is entirely negative, implying a decrease in saccade amplitude during the experiment (estimate = -0.06; 95% CI [-0.11, -0.02], EF = 91.59). For each combination of patterns, however, the HDI is strictly positive. The effect of the epoch is unequal for the different stimulus combinations. The trend in block effect is either negative or insignificant (estimated by the highest posterior density intervals of the entrends function at the first and the last experimental blocks). No clear difference between the groups is evident.  
The decrease in saccade amplitude may be interpreted as resulting from unconscious memory, which reduces the extent to which saccades are made to incorrect regions.  
Contrary to the results of [36], we did not find a negative correlation between the fixation duration and saccade magnitude. Our data showed a lack of correlation between the two characteristics of the eye movements (r = 0.09).  
Figure 12: Posterior distributions for the saccade amplitudes for all stimulus patterns: (**A**) for the stimuli from Group 1; (**B**) for the stimuli from Group 2; (**C**) for the stimuli from Group 3. The shaded regions correspond to the 90% credible intervals of the median.