One of the important sources of failures in visual working memory (VWM) is that individual items can interfere with each other. Here, we tested how two causes of such interference—poor categorical distinctiveness and imperfect feature binding—interact. In three experiments, we showed low and high distinctive objects and tested VWM for objects alone, for locations alone and for object-location conjunctions. We found that low object distinctiveness impairs object recognition and increases the number of object-location binding errors. Also, we dissociated the probabilities that these binding errors are due to recognition impairment or a failure of correct binding. Results show that poor distinctiveness increases binding errors rate only due to lacking recognition but not to binding impairment. Together, our findings suggest that object distinction and object-location binding act upon different components of VWM and are separate sources of interference. This study was funded by RSCF #18-18-00334.
Prevailing theories of visual working memory assume that each encoded item is stored or forgotten as a separate unit independent from other items. Here, we show that items are not independent, and that the recalled orientation of an individual item is strongly influenced by the summary statistical representation of all items (ensemble representation). We find that not only is memory for an individual orientation substantially biased towards the mean orientation, but the precision of memory for an individual item also closely tracks the precision with which people store the mean orientation (which is, in turn, correlated with the physical range of orientations). Thus, individual items are reported more precisely when items on a trial are more similar. Moreover, the narrower the range of orientations present on a trial, the more participants appear to rely on the mean orientation as representative of all individuals. This can be observed not only when the range is carefully controlled, but also shown even in randomly generated, unstructured displays, and after accounting for the possibility of location-based ‘swap’ errors. Our results suggest that the information about a set of items is represented hierarchically, and that ensemble information can be an important source of information to constrain uncertain information about individuals.
Eye-tracking is a non-invasive measure that has been repeatedly used for studying attention and related cognitive processes. While eye-tracking is not a direct measure of brain activity, it has been shown to reveal information about mental processes, that may not be easily accessible through other measures, such as problem solving strategies. Mental attentional capacity corresponds to the amount of information an individual can maintain and manipulate in mind (Pascual-Leone, J. ,1970); it is considered the central maturational component of working memory (Arsalidou, M., Pascual-Leone, J., & Johnson, J. ,2010). This construct has been found to be closely related to other aspects of cognitive competence and intelligence (Johnson et al., 2003). Research into relation between eye movements and mental attentional capacity across development at the moment is sparse and fragmented and no eye tracking studies have been conducted so far with parametric developmental measures, such as the colour matching tasks (Arsalidou, M., Pascual-Leone, J., & Johnson, J. ,2010), which would allow to dissociate changes in saccades and fixations related to working memory load (n = 6) from those related to interference control and trace the maturation of these two processes. The purpose of this study is to investigate the relation between eye-tracking indices (e.g., number of fixations) and mental attentional capacity. Data from adult participants showed significant differences between number of fixations per trial for different levels of mental attentional load. Additionally, analysis revealed significant negative correlation between number and duration of fixations and accuracy for both the balloons and the clowns versions of the task, with the correlation being stronger for the clowns version, which contains interference. Interestingly, for each difficulty level, children generate a similar number of fixations regardless of interfering features, whereas adults make fewer fixations when the task has less interfering features. This suggests that adults may have different strategies depending on the task. Increased number of fixations may indicate that children favor a visual-spatial strategy, whereas adults favor a verbal strategy.
The question of whether visual working memory (VWM) stores individual features or bound objects as basic units is actively debated. Evidence exists for both feature-based and object-based storages, as well as hierarchically organized representations maintaining both types of information at different levels. One argument for feature-based storage is that features belonging to different dimensions (e.g., color and orientations) can be stored without interference suggesting independent capacities for every dimension. Here, we studied whether the lack of cross-dimensional interference reflects genuinely independent feature storages or mediated by common objects. In three experiments, participants remembered and recalled the colors and orientations of sets of objects. We independently manipulated set sizes within each feature dimension (making colors and orientations either identical or differing across objects). Critically, we assigned to-be-remembered colors and orientations either to same spatially integrated or to different spatially separated objects. We found that the precision and recall probability within each dimension was not affected by set size manipulations in a different dimension when the features belonged to integrated objects. However, manipulations with color set sizes did affect orientation memory when the features were separated. We conclude therefore that different feature dimensions can be encoded and stored independently but the advantage of the independent storages are mediated at the object-based level. This conclusion is consistent with the idea of hierarchically organized VWM.
Previous research has documented the limited capacity of visual working memory (VWM) for color objects set at 3–5 items. Another line of research has shown that multiple objects can be stored in a compressed form of ensemble. However, existing data is more likely to testify that VWM can store no more than two such compressed units. But the nature of this discrepancy can be methodological: VWM for ensembles was never tested using methods that are applied in the research of VWM for objects. Here we have tested the capacity and precision of VWM for objects and ensembles using two standard methods — change detection and continuous report with a mixture model. We found that VWM for both types of units showed the similar capacity and precision when critical psychophysical parameters, such as foveal density and area are controlled. We also showed that this quantitative similarity between objects and ensembles is provided by a mechanism that represents each ensemble as a holistic VWM chunk as efficiently as it represents any single object.