## 4 Discussion  
### Influence of Complexity and Set Size  
Unlike the complexity of one-dimensional or two-dimensional objects in conventional digital interfaces, the complexity of 3D virtual objects in MAR interfaces involves various complex presentation forms of depth information and virtual-reality fusion information. No prior previous studies focused on how the virtual complexity affects users' perception of MAR information. Since VWM capacity is closely related to overall cognitive ability, it is important and necessary to reasonably control the complexity level and display the quantity of virtual elements when designing MAR interactions. It is not clear whether the VWM capacity for 3D virtual objects in MAR interfaces is fixed and how the complexity and quantity of 3D virtual objects displayed in MAR interfaces would affect VWM capacity. Here, we found evidence to answer these research questions by experimentally manipulating the complexity and number of 3D virtual objects in the MAR interface. This study assessed the correlations between the presentation form of 3D virtual objects and VWM capacity in MAR interactions based on a change detection paradigm. The results of reaction time, correct rate and Cowan's K showed that users' memory performance and VWM capacity were significantly better when the presentation number was 4 than when the presentation numbers were 6 and 8, and were significantly worse for high-complexity 3D objects than for medium- and low-complexity 3D virtual objects. Our study provides the following conclusions: (1) The user's behaviour in MAR interfaces is influenced by the complexity and quantity of 3D virtual objects displayed. (2) The highly complex 3D virtual objects can reduce the VWM capacity and memory precision. (3) The VWM capacity for 3D virtual objects in MAR interfaces is not fixed. These results provided strong evidence that the VWM capacity in MAR is modulated by the complexity and presentation quantity of displayed 3D virtual objects, and that the number of objects that can be stored decreases once complexity increases. These results are consistent with some previous studies on the relationship between item features and working memory, and they claimed that VWM capacity is affected by object complexity since the storage capacity for stimuli with simple features is greater than for those stimuli with complex features [57; 58; 59]. Our work builds on their research and demonstrates that in AR interfaces for mobile phones, the VWM capacity is limited not only by the number of 3D virtual objects but also by the number of features they contain (complexity). The significant differences between high and low complexity suggest that memory resources are flexibly allocated based on the complexity of each 3D virtual object in an MAR interface, that is, both internal variability (the complexity of 3D virtual objects) and external variability (presentation number) can lead to a change in VWM capacity. Consequently, as the complexity of the 3D virtual objects in the MAR interface increases, the number of resources allocated to each item decreases, leading to reduced memory capacity and lower memory accuracy. One explanation for the differing effects of complexity is offered by the precision of the representations. Previous studies have shown that VWM capacity is influenced by the information load of objects during the perceptual encoding phase, which decreases as processing difficulty increases [31]. Additionally, the allocation of memory resources is affected by the precision of the representations [60]. In our experiments, the complexity of the 3D virtual objects in the AR interface was also related to the precision of the representations in working memory. That is, highly complex 3D virtual objects contain higher demands for precision, which motivates subjects to work harder to retain more precise representations in memory. Thus, as the number of virtual features increases, more memory resources are consumed, which would affecting memory behaviour and capacity in change detection tasks.