Ayala S. Allon

How low can you go? Changing the resolution of novel complex objects in visual working memory according to task demands

In three experiments we manipulated the resolution of novel complex objects in visual working memory (WM) by changing task demands. Previous studies that investigated the trade-off between quantity and resolution in visual WM yielded mixed results for simple familiar stimuli. We used the contralateral delay activity as an electrophysiological marker to directly track the deployment of visual WM resources while participants preformed a change-detection task. Across three experiments we presented the same novel complex items but changed the task demands. In Experiment 1 we induced a medium resolution task by using change trials in which a random polygon changed to a different type of polygon and replicated previous findings showing that novel complex objects are represented with higher resolution relative to simple familiar objects. In Experiment 2 we induced a low resolution task that required distinguishing between polygons and other types of stimulus categories, but we failed in finding a corresponding decrease in the resolution of the represented item. Finally, in Experiment 3 we induced a high resolution task that required discriminating between highly similar polygons with somewhat different contours. This time, we observed an increase in the item’s resolution. Our findings indicate that the resolution for novel complex objects can be increased but not decreased according to task demands, suggesting that minimal resolution is required in order to maintain these items in visual WM. These findings support studies claiming that capacity and resolution in visual WM reflect different mechanisms.

Gestalt grouping cues can improve filtering performance in visual working memory

As part of filtering irrelevant information from entering visual working memory (VWM) and selecting only the relevant information for further processing the system should first tag the pieces of information as relevant or irrelevant. We manipulated difficulty of tagging items as relevant or irrelevant by applying perceptual grouping cues to investigate if it can improve filtering performance in VWM. Participants performed a change-detection task with three targets, six targets, or three targets and three distractors (filtering condition) in the memory display, and were asked to remember the colors (Experiments 1–2) or the orientations (Experiments 3–5) of the targets and ignore the distractors. In the filtering conditions, either the targets (Experiments 1, 3, and 4) or the distractors (Experiments 2 and 5) formed an illusory object (a Kanizsa triangle), appeared in a triangle-like configuration (grouping by proximity), or appeared at random positions (non-grouping). Grouping the targets improved filtering performance relative to non-grouping. Moreover, the illusory object cue further improved filtering performance beyond a proximity cue, but only when the cue was compatible with the task. When the distractors were grouped, the proximity cue improved filtering performance, and the illusory object cue, despite being a potent grouping cue, failed to improve filtering performance when it was compatible with the task. We suggest that the grouping cues advanced tagging of the grouped items. Yet, when the grouping cue strongly enhanced processing of the distractors, the tagging failed, such that the preliminary process of estimating incoming items led to full processing of the grouped items.

Compensation mechanisms that improve distractor filtering are short-lived

We investigated possible compensation mechanisms for improving filtering of distractors from entering visual Working Memory (WM). Participants preformed a change-detection task in which three targets, six targets, or three targets along with three distractors (the filtering trial) were randomly presented. In six experiments, we tried to reduce the filtering cost, calculated as the difference in accuracy between the three targets and the filtering condition, by either cueing the possible locations of the distractors using placeholders (that could be either fixed throughout the experiment or change every trial; i.e., location cue), or by providing the location cue coupled with a warning cue singling the upcoming filtering trial. Results revealed that the filtering cost was not reduced by a fixed location cue (Experiment 1 and Experiment 5). However, the fixed location cue coupled with a warning cue (Experiment 2 and Experiment 5) or a location cue that changed positions every trial (Experiment 6), were sufficient to reduce the filtering cost. Additionally, longer preparation interval for filtering trials did not further reduce the filtering cost (Experiment 3). We argue these findings support that in the context of visual WM, spatial filtering settings can only be held for a limited amount of time. Thus, these filtering settings must be reactivated in order to be effective and to reduce the filtering cost.

Correction to: Gestalt grouping cues can improve filtering performance in visual working memory

The original version of this article unfortunately contained a mistake.

The number of objects determines visual working memory capacity allocation even for complex items

We examined whether visual working memory (WM) capacity allocation is determined solely by complexity, with the number of objects being redundant, as suggested by flexible resource models. Participants performed the change detection task with random polygons as stimuli, while we monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as WM capacity load increases. In Experiment 1, we presented random polygons together with other complex items (e.g., shaded cubes and Chinese characters) and decreased the resolution with which random polygons need to be maintained in WM by introducing only between-category changes (e.g., polygon to cube). The results indicated that the polygon still consumed more WM capacity relative a simple object. In Experiment 2, we compared the WM maintenance of one whole polygon to two halves of a polygon, thus equating complexity but manipulating the number of items. Additionally, we compared the whole polygon to a single half of a polygon, equating the number of items but varying the complexity level. The results suggested that only the number of objects determined WM capacity allocation: the CDA amplitude was lower in the whole polygon condition relative to the two halves condition, even though both contained the same amount of information. Furthermore, the CDA was identical when comparing one whole polygon to one polygon half, even though these conditions differed in complexity. Experiment 3 extended these results by showing that two polygon-halves moving separately but then meeting and moving together, were gradually integrated to consume similar WM capacity as one polygon half. Interestingly, we also found an object benefit in accuracy, corroborating the important role of objects in WM. Our results demonstrate that WM capacity allocation is highly sensitive to objecthood, as suggested by discrete slot models. Meeting abstract presented at VSS 2015.