The visual working memory (VWM) system is widely regarded as the cornerstone of cognitive functions, which bridge the external environment and mind (Baddeley, 1992; Cowan, 1999). Previous studies show that participants can only remember 3–4 simple items in a VWM task (Luck and Vogel, 1997). Although individuals can improve the precision of VWM representation by sacrificing the amount number of stored representations (Gao et al., 2011; Machizawa et al., 2012; Ye et al., 2017, 2019; Long et al., 2020), the view that VWM is limited in its storage capacity is widely accepted (Vogel et al., 2001; Alvarez and Cavanagh, 2004). In the face of the dynamically presented visual information, the memory representations were conferred with different priorities according to the task demands during the highly complex tasks (Ericsson and Kintsch, 1995; Rose, 2020; Stokes et al., 2020). In light of embedded processes models of working memory (Cowan, 1999; Oberauer, 2002, 2005), the memory items greatly attended were retained in the region of direct access (RDA) serving for the current processing, one of which was represented in the focus of attention (FOA); that was termed as the active state. Those items that were less relevant to the immediate task were maintained in the activation region of long-term memory (aLTM), and got accessed when needed later; they were regarded to be held in the passive state (LaRocque et al., 2014; Peters et al., 2019; Li et al., 2020, 2021; Zhang et al., 2022). Regarding the associative network of memory representations, the memory representations were deemed to be retained in distinct states according to the relevance to the current task, with the “state” signaling the accessibility of a representation for ongoing cognitive processing (Olivers et al., 2011; Stokes et al., 2020; Zhang et al., 2022). The memories in the active state are characterized by most privilege and direct accessibility, while the passive memories are accessed indirectly through links to the active representation (Oberauer, 2001; Oberauer and Lange, 2009; Peters et al., 2019).

During the memory task with multiple items, individuals widely adopted the chunking strategy, which rendered the memory functioning more efficient. Chunking means the links between items are generated (Ericsson and Kintsch, 1995; Oberauer, 2002). Notably, the working memory system was primarily responsible for the links of item–item and item–context, while the strength of links relied on the relation between items (Oberauer, 2002; Oberauer and Lange, 2009; Kaiser et al., 2015; Liu et al., 2022). Accordingly, we might suppose that these items with identical information tended to build up strengthening links relative to the unidentical items. When one item was activated, its linked item could be automatically activated via the associative links (Oberauer, 2005).

According to the embedded process models, it was proposed that the memory items were automatically bound to their positions in RDA, and the links between related memory items were spontaneously established (Oberauer and Lange, 2009). Given that the memory items with identical information were more likely to be chunked together with the strong associative links, it was assumed that the memory representations could be readily activated by means of the associative links when the other representations that were linked to it were activated. Thus, we could reasonably reckon that these memory representations that were possessed with the same feature were conferred with a low activation threshold of achieving the activation state relative to those memory items, which greatly differed. Accordingly, activation of memory representations with the same feature could require less resources due to the low activation threshold, thereby the spared resources preferably being used to enhance the memory performance. If it was the case, we predicted that the memory precision should be enhanced when presenting more identical items, while the spatial information of memory items might play a role. Thus, that opened up the question of whether the strong associative links between identical items could contribute to better memory performance, that is, the facilitating effect of identical objects.

In this study, we attempted to explore the facilitating effect of identical objects by measuring the precision and quantity of memory representations in color recall tasks. Based on the definition of an identical object, we defined the two bars with the same orientation as the identical objects. The bar’s orientation should be remembered precisely during the encoding and retention period and retrieved later when probed. The size of the memory set did never exceed the memory capacity (no more than four items), which ensured the successful encoding of all memory items (Luck and Vogel, 1997; Cowan, 2001).

We manipulated the number of identical objects to assess the facilitating effect of identical objects in Experiment 1, generating three conditions, two pairs of identical objects (2-pair), one pair of identical objects (1-pair), and no identical objects (0-pair). Considering that the size of the memory set was less than four, the memory quantity was comparable across the three conditions. We predicted that, if the facilitating effect of identical objects existed, the memory precision in the 2-pair and 1-pair conditions would be better than that of the 0-pair condition; if not, the memory precision in the three conditions did not differ.

In this part, we aimed to explore the effect of location information on the facilitating effect of identical objects. The locations of identical objects were manipulated. Based on the experimental conditions in Experiment 1, we designed the horizontal condition (2-pair-horizontal), vertical condition (2-pair-vertical), diagonal condition (2-pair-diagonal), and four unidentical conditions (4-object). There were two pairs of identical objects in each condition. In addition, there was a condition of presenting two unidentical items as baseline (2-object).

This current study attempted to explore whether the memory performance of identical objects could be enhanced due to the strengthening links between them across three experiments. We varied the number of identical items in Experiment 1, and these results showed that the memory precision was higher when more identical items were presented, indicating the facilitating effect of identical objects. Given that the memory items were automatically bound with spatial context according to the binding mechanisms (Oberauer, 2002; Oberauer and Lange, 2009), the location information of memory items should be taken into account. In addition to the horizontal and vertical conditions, two pairs of identical items were located diagonally in Experiment 2. We observed the absence of facilitating effect of identical items. However, it was premature to consider that the facilitating effect completely relied on space proximity (Shepard, 1962). Furthermore, Experiment 3 examined what the effect the spatial location on the facilitating effect. In this part, the identical items were always presented diagonally and differed in the quadrant. It was found that the identical items in the second and fourth quadrants still conferred with facilitating effect, but rather in the first and third quadrants. Overall, we concluded that the object sameness contributed to better memory performance, evidencing the facilitating effect of identical objects; that facilitating effect was conditioned by the spatial context, thus not extended to the identical objects that were presented in any random positions.

In terms of the memory system, the associative network of memory representations was established via the abundant links between related representations. The high relevance between the representations preferentially contributed to strengthening links. In the current study, the memory precision acted as the behavioral indicator of the linking strength of memory representations, which to some certain revealed that physically identical objects produced relatively stronger links than unidentical objects. Notably, the linking strength was conditioned by location information, which at least complied with the proximity of the Gestalt principle (Peterson and Berryhill, 2013; Shen et al., 2014).

Moreover, it has previously been proposed that spatial information plays an important role. When visual stimuli appeared within the field of vision, individuals would involuntarily focus on a specific visual field, which resulted in the preferable processing of the stimuli in the focused visual field over other unfocused visual fields. That was referred to as spatial bias (Ossandon et al., 2014). The facilitating effect from the identical objects located in the second and fourth quadrants might be accounted for by the spatial bias that was thought to derive from the interaction between sensory attention and motor intentional (Schwartz et al., 1997). For example, a previous study has found that the left visual field bias worked during the early perception of face stimuli. That bias was presumed to be accounted for by the hemisphere lateralization or the product of control by high-lever brain areas. In addition, the social culture might also have an effect on spatial bias. Brady et al. (2005) found that, for example, people tended to depend on the expressions of the left face for making a response when the left and right faces wore different expressions during a face discrimination task; however, the left bias was absent for those people who habitually wrote and read from right to left.

The research on spatial bias previously suggested that participants showed a leftward bias in the early period of visual research, independent of the stimuli category (Ossandon et al., 2014). In addition, a study on the gaze bias had revealed that individuals tended to gaze at the upper-left location in the initial gaze movement when they performed a visual search; in addition, the upper-left and lower-right parts were thought as favored locations, though depending on conditions (Durgin et al., 2008). That is, we are more likely to focus on the top part when the attention shifted to the left visual field, while the focus was put on the down part when attending to the right visual field. Intriguingly, this research on the spatial bias convergingly pointed to the second or/and fourth quadrants, which was compatible with the findings of the current study. Though there was no agreement on the quadrant edge, it seemed to presume that the second quadrant was widely regarded to be the most prioritized.

The sameness of memory items should be regarded as the extremity of the similarity of memory items. There were two theoretical interpretations that might underpin the facilitating effect of similarity. First, it has been pointed out that the enhanced memory performance resulted from the simplification of the memory array due to the similarity of memory items, thus indirectly reducing the memory load and lowering the need for cognitive resources (Mate and Baques, 2009). However, Lin and Luck (2009) argued that better memory performance of similar items was attributed to reciprocal facilitation (Lin and Luck, 2009). The current results pattern suggested that the guess rate was low and comparable across different conditions, indicating that the number of memory items successfully encoded in VWM did not differ. That thus denied the reducing memory load account. In addition, considering that the memory precision should reach an asymptote when the load reached four, intriguingly, the memory precision was modulated by the number of identical items through which four items were remembered, which implied the reciprocal facilitation between the identical items via strengthening links. That seemed to be consistent with Lin’s proposal.

Overall, the current study evidenced the facilitating effect of identical objects, while the facilitating effect was affected by location information (i.e., spatial bias). In further research, it was necessary to investigate what the role of spatial distance and configuration in the facilitating effect of identical objects. Given that the facilitating effect was observed from two identical objects in the current study, the present findings paved the way for further exploration of whether the facilitating effect was larger if the number of identical objects was more than two, and whether the facilitating effect had a similar level when increasing the overall memory load. Future research on these questions would benefit from a complete understanding of the maintenance mechanisms of identical items.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Research Ethics Committee of Liaoning Normal University. The patients/participants provided their written informed consent to participate in this study.

GR and NM developed the study concept and designed the experiment, performed the data analysis, and provided critical revision. NM performed testing and data collection. GR, NM, and ML interpreted the data. ML drafted the manuscript and refined the language. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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