General Discussion

6.1.1 Effect of local/global priming on color appearance

 In the present study, I examined whether the local/global priming task affected the color ap- pearance on the color contrast between the successive and simultaneous adjusting. In Exp.1, there was a significant difference in the value ofτbetween the local and global priming con- ditions on the contrast using the successive adjusting. In Exp.2, there was not significant difference in the value ofτbetween the local and global priming conditions on the contrast using the simultaneous adjusting. My findings showed that local/global priming task affected color appearance on color contrast depending on the adjusting conditions. Several factors, such as the attentional window or the short-term memory, might be involved in these results since Exp.1 and Exp2 showed different results.

 The attentional window is limited spatial range to which attention is allocated [40, 41].

In Figure 3.4.2, the participants perceived the different color from the physical color in the global priming task than in the local priming task. As for the attentional window, there are two possible factors related to my results. Firstly, the results in Exp.1 suggest that the global priming effect would increase the size of the attentional window and the participants would perceive globally the color appearance including the distractors, whereas the local priming effect would reduce the size of the attentional window and they would perceive locally the color appearance on the target color more accurately. On the contrary to Exp.1, in Exp.2, the broader range of the focus than the size of the attentional window modulated by local/global priming could be reflected in the stimuli. The participants had to adjust the test color while looking at the target color in Exp.2. This process requires a broader range of focus to compare exactly the test color with the target color. These assumptions are suggested by the following findings. Several studies suggest that globally directed attention tended to involve the right hemisphere, while locally directed attention tended to involve the left hemisphere [5, 6, 7], the right hemisphere being more adept at processing early-available low frequencies and the left hemisphere operating more efficiently on later-available low frequencies [8, 9]. These spatial frequencies were also mentioned in the perspective of the pupil. Sabatino et al. (2018) carried out an experiment using the Navon figure to investigate how pupil size changes in

the processing of local/global letters. Their results showed that there was a difference in the baseline pupil diameter between the processing of local and global letters and the baseline pupil diameter in the processing of local letters was significantly lower than that in the pro- cessing of global letters. They reported that the change in the pupil diameter was significant when in the local perception but when in the global perception [42]. It has been reported that the pupil dilation leads to focusing on the broad scope and the image on the retina ap- pears more blurred, while the pupil contraction leads to focusing on the narrow scope and the image on the retina appears more detailed [43]. The pupil diameter also varies with the at- tention. Mathˆot et al. (2013) showed that the pupillary light response (PLR) is modulated by the brightness of covertly attended objects [44]. Tkacz and Yeshurun (2018) showed that the diameter of the attentional window was at least 2° by measuring PLR [45]. They reported the pupil size was modulated when they were 1° away from the attended letter, but not when this distance was larger. These studies support my prediction that the range of the focus on the color contrast using simultaneous adjusting might be broader than the size of the attentional window modulated by local/global priming.

  Secondly, with the attentional window, the distractors and the effect of the background color area were involved with the results. The stimuli sizes were different between Exp.1 and Exp.2 in this study. Considering the distractors, the following assumption will be obtained.

In Exp.1’s case of the distractors, the size of the attentional window modulated by the local priming task focused on only the target color, while the size of the attentional window modu- lated by the global priming task focused on target color including in the distractors. In Exp.2’s case of the distractors, the overall stimulus size was adjusted to match the size of the big letter.

The size of the attentional window modulated by local and global priming tasks focused on almost the same range, such as target color included in the distractors, since each distractor and target color in Exp.2 was closer than in Exp.1. The same as the distractions, the back- ground color might affect the current results. In Exp.1’s case of the background color range, the size of the attentional window modulated by local priming task focused on the target color with the narrow background, while the size of the attentional window modulated by global priming task focused on target color with the broad background. In Exp.2’s case of the back- ground color area, the size of the attentional window modulated by local and global priming task focused on almost the same background color range since the background color range in Exp.2 was smaller than in Exp.1. These assumptions are suggested by the following findings.

Hine and Ito (2014) reported that the performance of the face recognition task after reading letters in the Navon figures was different depending on the size of Navon figure. Furthermore, Graham and Brown (1965) and Kirschmann (1891) showed that a smaller target color area compared to the surrounding color area induces a larger color contrast effect[36, 37]. Given the uncertain size of the attentional window modulated by the local/global priming task, the color perception could be affected by the distractors or background color area.

 Considering the involvement of the attentional window in my results, the following as- sumption might be shown. Mundy (2014) indicated that the local/global processing could be involved with the higher-order visual areas. However, if the local/global processing is directly involved with higher-order visual areas, there should be no differences between the successive and simultaneous adjusting. My results did not show the same effect due to the local/global priming task throughout Exp.1 and Exp.2. These findings suggest that the lo-

cal/global processing directly affects the size of the attentional window related to lower-order visual processing, then resulted in perceiving the local features with the narrow size of the attentional window.

 As for the short-term memory, the local/global priming tasks could affect short-term mem- ory. The result in Exp.1 suggests that the memory retrieval of the contextual color was af- fected by local/global priming, then the participants adjusted the color on the test figure, taking retrieved contextual colors into account. By contrast, the result in Exp.2 showed no priming effect since the simultaneous constant did not require memory retrieval from the short-term memory. Olkkonen et al. (2014) reported that the short-term memory influenced the contextual color processing in a way that was consistent with the observer taking prior information into account, depending on the variability in the sensory signal [46]. Lewis et al.

(2009) tested the face recognition task when the local/global priming task was conducted be- fore the encoding and recognition phase [47]. The result showed that the accuracy of the face recognition was different depending on the local or global priming in the both phase encod- ing and recognition. The performance of face recognition after the global priming task was higher than after the local priming task when the global priming task was required before the encoding phase and vice versa. These studies support that the performance of the short-term memory affected by the local/global priming task could be involved with the result of color perception in this study. Although there was no phase of memory retrieval in Mundy’s (2014) experiment using M¨uller-Lyer illusion, the local/global priming task affected the magnitude of the illusion. This may be because the process of memory is less important in the M¨uller- Lyer illusion than in the color contrast illusion. It is required to examine further experiments using various illusions for the discussion about the involvement of memory.

6.1.2 Influence of local/global perceptual style on color appearance

 In Exp.1, There was not significant correlation between the value of τand the index of global precedence (the perceptual style) on the contrast using the successive adjusting. In Exp.2, there was a negative correlation between the color appearance and the perceptual styles on the contrast using the simultaneous adjusting. These results suggest that the differ- ence in perceptual style between the local and global affects the color perception depending on the adjusting conditions. Several factors could be involved with individual differences.

For instance, even though the participants with a local perceptual style had to focus on the Target color in my experiments, they also unconsciously considered the influence of the Filter color and reference color, which led to a larger color appearance than in case of the partici- pants with the global perceptual style. The reason that there were no individual differences in Exp.1 could be explained by the fact that the presentation time was shorter than in Exp.2.

This assumption is supported by Hine and Tsushima (2018), They examined how individual perception style (global or local) correlated with the implicit and explicit memory. They re- ported that people with a local perceptual style have a tendency to unconsciously unrelated encode information [35]. Therefore, The unconsciously unrelated encode with the local per- ceptual style could relate to the color perception in my results.

 Working memory (WM) could also be a possible factor contributing to the current results.

WM indicates the concept of information processing functions such as information retention,

manipulation and conversion during the performance of various cognitive functions such as conversation, reading, calculation and reasoning [48]. The result in this study suggests that the participants with a global perceptual style have a tendency to have higher WM capacity and the participants with a local perceptual style have a tendency to have lower WM capacity.

In addition, the difference in the color appearance could be larger for the high WM capac- ity than for the low WM capacity. These assumptions are based on the following findings.

Elizabeth et al. (2011) reported that there was a difference in the color constancy between higher and lower WM capacities. The higher WM group showed significantly better succes- sive color constancy than the lower WM group. However, the lower WM group performed reasonably well in the complex-background condition [49]. They suggested that WM ability was a difference in the ability to control attention. For a person with a high WM capacity, it may be easier to maintain attention on the target, independent of the background conditions.

By contrast, a person with low WM capacity may not be able to maintain attention on the target and instead scans also the different colored patches surrounding the target to attain im- proved color constancy. Some reports also suggest that the Navon figure is involved with WM capacity[50, 51]. Goodhew (2021) examined whether individual differences in the attentional resizing efficiency were related to WM capacity. The results showed that people with high WM capacity may have more readily adopted the dominant attentional breadth to the global level, thereby incurring a greater cost on the infrequent trials requiring resizing to the local level [52]. Therefore, these findings suggest that the attentional way varied depending on the local/global perceptual style contributes to WM capacity and this resulted in individual differ- ences in the color appearance. Given that the higher WM group showed significantly better successive color constancy than the lower WM group [49], the difference in the color appear- ance should be larger for the global perceptual style than for the local perceptual style. While on the contrary, the results of the local/global perceptual style in the present study showed that the difference in the color appearance was larger for a participant with a local perceptual style than for a participant with a global perceptual style. Therefore, the WM could not fully account for the current results. For investigation of the influence of WM on the perceptual style, additional experiments are required. When successful task performance requires atten- tional control, correlations with WM capacity are often found [53]. If the attentional window is related to my result, consideration of WM involvement will be a significant factor.