Sequential encoding aids working memory for meaningful objects’ identities but not for their colors

Abstract

Previous studies have found that real-world objects' identities are better remembered than simple features like colored circles, and this effect is particularly pronounced when these stimuli are encoded one by one in a serial, item-based way. Recent work has also demonstrated that memory for simple features like color is improved if these colors are part of real-world objects, suggesting that meaningful objects can serve as a robust memory scaffold for their associated low-level features. However, it is unclear whether the improved color memory that arises from the colors appearing on real-world objects is affected by encoding format, in particular whether items are encoded sequentially or simultaneously. We test this using randomly colored silhouettes of recognizable vs. unrecognizable scrambled objects which offer a uniquely controlled set of stimuli to test color working memory of meaningful vs. non-meaningful objects.Participants were presented with four stimuli (silhouettes of objects or scrambled shapes) simultaneously or sequentially. After a short delay, they reported either which colors or which shapes they saw in a 2AFC task. We replicated previous findings that meaningful stimuli boost working memory performance for colors (Exp. 1). We found that when participants remembered the colors (Exp. 2) there was no difference in performance across the two encoding formats.However, when participants remembered the shapes and thus identity of the objects (Exp. 3), sequential presentation resulted in better performance than simultaneous presentation. Overall, these results show that different encoding formats can flexibly impact visual working memory depending on what the memory-relevant feature is.

Fluid intelligence correlates with working memory capacity for both real-world objects and simple-feature stimuli

“…This points to possibly important differences when thinking of measuring working memory capacity. For instance, previous findings showed a greater benefit of sequential presentation for meaningful stimuli compared to abstract stimuli, as it allows for deeper semantic processing of each stimulus (Brady & Störmer, 2022;Chung et al, 2023b). Our data suggest that when stimuli are presented sequentially, real-world objects also result in higher reliability compared to sequentially presenting colored-circles, comparable to the reliability level of simultaneous presentation of colored circles.…”

“…Stimuli (150 px in width and 150 px in height) were presented one at a time at the central location of the screen for 200 ms each, with a 200 ms inter-stimulus-interval. We adopted a sequential presentation of the stimuli to maximize performance differences between these tasks, following recent work showing a larger real-world object benefit for sequential relative to simultaneous stimulus presentation (Brady & Störmer, 2022;Chung et al, 2023b). After a 800ms delay participants were presented with a two-alternative-forced-choice (2-AFC) test in the center of the screen with two different stimulus choices: one matching one of the stimuli at encoding (target) and one that was a novel foil.…”

Conceptual information of meaningful objects is stored incidentally.

“…However, participants’ overall performance was very high, suggesting that this lack of difference may have been due to ceiling performance, especially in light of previous studies showing that meaningful stimuli resulted in better working memory performance than nonmeaningful stimuli (e.g., Brady & Störmer, 2022; Chung et al, 2023b). A recent study that used the exact same stimulus set as here and tested explicit working memory for object identity using set size 4, for instance, found benefits for meaningful identities relative to scrambled versions at these higher set sizes (Chung et al, 2023c). In fact, in our replication Experiments 1R and 2R, there was also a small but reliable meaningfulness advantage in the postsurprise shape trials.…”

Meaningfulness and familiarity expand visual working memory capacity

“…and not just in terms of its low-level visual dimensions (Asp et al, 2021) The framework of a hierarchically structured working memory system, where lower-level representations are directly linked with higher-level representations, predicts that even simple, low-level features should be influenced by the meaningfulness of a stimulus. Indeed, recent studies found that this is the case: working memory performance for simple low-level features that are not themselves meaningful is increased if they are encoded in a meaningful context (Allen et al, 2021;Chung et al, 2023a;Chung et al, 2023b). Specifically, when participants were asked to remember just the colors of a set of objects, they had stronger memories for these colors when they were part of real-world objects (or recognizable silhouettes) compared to unrecognizable or scrambled shapes.…”

“…These findings suggest that encoding format and strategy matter for visual working memory and may differentially affect performance depending on stimulus type. Specifically, while sequential encoding might be particularly beneficial for recognizable and meaningful objects, this may not be the case for simple visual features (Brady & Störmer, 2022;Chung et al, 2023a) where other encoding strategies, such as ensemble processing or chunking play a larger role (Chunharas & Brady, 2023). Thus, how information is encoded can modify its representational structure.…”