Reorganization of spatial configurations in visual working memory

Processing spatial configurations in visuospatial working memory is influenced by shifts of overt visual attention

When memorizing multiple objects, humans process them in relation to each other, proposing a configuration benefit. Shifts in overt visual attention through eye movements might influence the processing of spatial configurations. Whereas some research suggests that overt visual attention aids the processing of spatial representations, other research suggests a snapshot-like processing of spatial configurations, thus likely not relying on eye movements. In the first experiment, we focused on the comparison between an enforced fixation and a free view condition regarding configurational effects. Participants encoded objects' locations and were asked for changes at retrieval. One object was displaced in half of the trials and was either accompanied by a configuration or was displayed alone. In the second experiment, we expanded this idea by enforcing fixation during different task phases, namely encoding, maintenance and retrieval. We investigated if a fixed gaze during one specific phase drives the influence of eye movements when processing spatial configurations. We observed reliable configuration benefits for the free view conditions. Whereas a fixed gaze throughout the whole trial reduced the effect, enforced fixations during the task phases did not break the configuration benefit. Our findings suggest that whereas the processing of spatial configurations in memory is supported by the ability of performing shifts of overt visual attention, configurational processing does not rely on these shifts occurring throughout the task. Our results indicate a reciprocal relationship of visuospatial working memory and eye movements.

Topological change induces an interference effect in visual working memory

The “irrelevant-change distracting effect” refers to the effect of changes in irrelevant features on the performance of the target feature, which has frequently been used to study information processing in visual working memory (VWM). In the current study, we reported a novel interference effect in VWM: the topological-change interference effect (TCIE). In a series of six experiments, we examined the influence of topological and nontopological changes as irrelevant features on VWM using a color change detection paradigm. The results revealed that only topological changes, although task irrelevant, could produce a significant interference effect. In contrast, nontopological changes did not produce any evident interference effect. Moreover, the TCIE was a stable and lasting effect, regardless of changes in locations, reporting methods, particular stimulus figures, the other salient feature dimensions and delay interval times. Therefore, our results support the notion that topological invariance that defines perceptual objects plays an essential role in maintaining representations in VWM.

Remembering nothing: Encoding and memory processes involved in representing empty locations

Previous research has provided rich evidence that a set of visual objects can be encoded in isolation along with their exact coordinate positions as well as a global configuration that provides a network of interrelated spatial information. However, much less data is available on how unoccupied locations are encoded and maintained in memory. We tested this ability in adults using a novel paradigm that involved both empty and filled locations and required participants to monitor the addition or deletion of an item, which occurred 50% of the time. Crucially, a number of locations remained hidden to the participant-thus, information on the absence of an item at a location could not be inferred from the presence of items elsewhere. We used eye-tracking to measure the proportion of target looking during encoding and the amount of pupil dilation during memory retention. Participants looked significantly longer at filled compared with empty targets, and target looking during encoding only predicted accuracy in case of filled targets. Increased pupil dilation was observed in response to an increasing number of items, while pupil diameter was unaffected by the number of empty locations. In addition, participants made significantly more errors in the conditions that involved the representation of an empty location. Our findings support the view that human adults encode exact coordinates of items in memory. In contrast, we suggest that empty locations are represented as a property of the global configuration of items and empty space, and not as independent units of information.

Incidental encoding of visual information in temporal reference frames in working memory

Visual events are structured in space and time, yet models of visual working memory (VWM) have largely relied on tasks emphasizing spatial aspects. Here, we show that temporal properties of visual events are incidentally encoded along with spatial properties. In five experiments, participants performed change-detection tasks, in which items had unique spatial and temporal coordinates at encoding. Crucially, neither space nor time was task-relevant. The key manipulation concerned the retrieval context: The test array was identical to the memory array either in its entire spatiotemporal structure, or only its spatial or temporal structure. Removing spatial or temporal information at retrieval resulted in costs, indicating that memory relied on both spatial and temporal context in which items were initially perceived. Encoding of spatiotemporal structure occurred incidentally, not strategically, as it was robust even when the retrieval context was perfectly predictable. However, spatial and temporal inter-item spacings influenced the weighting of spatial and temporal information: It favoured the domain in which items were more widely spaced, facilitating their individuation and, likely, access to representations. Across individuals, the weighting of spatial and temporal information varied substantially, but it remained consistent across sessions, suggesting stable preferences for coding in the spatial or temporal domain. No comparable incidental encoding occurred for other task-irrelevant feature dimensions (size or colour). We propose that temporal structure serves as fundamental a function in VWM as spatial structure, scaffolding events that unfold over time.

Reorganization of spatial configurations in visual working memory: A matter of set size?

Humans process single objects in relation to other simultaneously maintained objects in visual working memory. This interdependence is called spatial configuration. Humans are able to reorganize global spatial configurations into relevant partial configurations. We conducted three experiments investigating the process underlying reorganization by manipulating memory set size and the presence of configurations at retrieval. Participants performed a location change detection task for a single object probed at retrieval. At the beginning of each trial, participants memorized the locations of all objects (set size: 4, 8, 12, or 16). During maintenance, a valid retro cue highlighted the side containing the object probed at retrieval, thus enabling participants to reorganize the memorized global spatial configuration to the partial cued configuration. At retrieval, the object probed was shown together with either all objects (complete configuration; Experiment 1a), the cued objects only (congruent configuration; all Experiments), the non-cued objects only (incongruent configuration, all Experiments) or alone (no configuration; Experiment 1b). We observed reorganization of spatial configurations as indicated by a superior location change detection performance with a congruent partial configuration than an incongruent partial configuration across all three experiments. We also observed an overall decrease in accuracy with increasing set size. Most importantly, however, we did not find evidence for a reliable impairment of reorganization with increasing set size. We discuss these findings with regard to the memory representation underlying spatial configurations.