Dataset Information

Reconstructions of information in visual spatial working memory degrade with memory load.

ABSTRACT: Working memory (WM) enables the maintenance and manipulation of information relevant to behavioral goals. Variability in WM ability is strongly correlated with IQ [1], and WM function is impaired in many neurological and psychiatric disorders [2, 3], suggesting that this system is a core component of higher cognition. WM storage is thought to be mediated by patterns of activity in neural populations selective for specific properties (e.g., color, orientation, location, and motion direction) of memoranda [4-13]. Accordingly, many models propose that differences in the amplitude of these population responses should be related to differences in memory performance [14, 15]. Here, we used functional magnetic resonance imaging and an image reconstruction technique based on a spatial encoding model [16] to visualize and quantify population-level memory representations supported by multivoxel patterns of activation within regions of occipital, parietal and frontal cortex while participants precisely remembered the location(s) of zero, one, or two small stimuli. We successfully reconstructed images containing representations of the remembered-but not forgotten-locations within regions of occipital, parietal, and frontal cortex using delay-period activation patterns. Critically, the amplitude of representations of remembered locations and behavioral performance both decreased with increasing memory load. These results suggest that differences in visual WM performance between memory load conditions are mediated by changes in the fidelity of large-scale population response profiles distributed across multiple areas of human cortex.

SUBMITTER: Sprague TC

PROVIDER: S-EPMC4181677 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Reconstructions of information in visual spatial working memory degrade with memory load.

Sprague Thomas C TC Ester Edward F EF Serences John T JT

Current biology : CB 20140904 18

Working memory (WM) enables the maintenance and manipulation of information relevant to behavioral goals. Variability in WM ability is strongly correlated with IQ [1], and WM function is impaired in many neurological and psychiatric disorders [2, 3], suggesting that this system is a core component of higher cognition. WM storage is thought to be mediated by patterns of activity in neural populations selective for specific properties (e.g., color, orientation, location, and motion direction) of m ...[more]

PMID: 25201683

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Project description:Ample research in visual working memory (VWM) has demonstrated that the memorized items are maintained in integrated spatial configurations, even when the spatial context is task irrelevant. These insights were obtained in studies in which participants were provided with the information they memorized. However, the encoding of provided information is only one aspect of memory. In everyday life, individuals often construct their own memory representations, an aspect of memory we have previously termed self-initiated (SI) working memory. In this study, we employed a SI VWM task in which participants selected the visual targets they memorized. The spatial locations of the targets were task irrelevant. Nevertheless, we were interested to see whether participants would construct spatially structured memory representations, which would suggest that they intended to maintain the visual targets as integrated spatial configurations. The results of two experiments demonstrated that participants constructed spatially structured configurations relative to random displays. Specifically, participants selected visual targets in close spatial proximity and constructed spatial sequences with short distances and fewer path crossings. When asked to construct configurations for a hypothetical competitor in a memory contest, participants disrupted the spatial structure by selecting visual targets that were further apart and by increasing the distances between them, which suggests that these characteristics were under their control. At the end of each experiment, participants provided verbal descriptions of the strategies they used to construct the memory displays. While the spatial structure of the SI memory representations was robust, it was absent from the participants' explicit descriptions, which focused on non-spatial strategies. Participants reported selecting items based, most frequently, on semantic categories and visual features. Taken together, these results demonstrated that participants had access to the metacognitive knowledge on the spatial structure of VWM representations, knowledge they manipulated to construct memory representations that enhanced or disrupted memory performance. While having a profound impact on behavior, this metacognitive knowledge on spatial structure remained implicit, as it was absent from the participants' verbal reports. Viewed from a larger perspective, this study explores how individuals interact with the world by actively structuring their surroundings to maximize cognitive performance.

Project description:BackgroundVisual working memory (VWM) helps us store visual information to prepare for subsequent behavior. The neuronal mechanisms for sustaining coherent visual information and the mechanisms for limited VWM capacity have remained uncharacterized. Although numerous studies have utilized behavioral accuracy, neural activity, and connectivity to explore the mechanism of VWM retention, little is known about the load-related changes in functional connectivity for hemi-field VWM retention.Methodology/principal findingsIn this study, we recorded electroencephalography (EEG) from 14 normal young adults while they performed a bilateral visual field memory task. Subjects had more rapid and accurate responses to the left visual field (LVF) memory condition. The difference in mean amplitude between the ipsilateral and contralateral event-related potential (ERP) at parietal-occipital electrodes in retention interval period was obtained with six different memory loads. Functional connectivity between 128 scalp regions was measured by EEG phase synchronization in the theta- (4-8 Hz), alpha- (8-12 Hz), beta- (12-32 Hz), and gamma- (32-40 Hz) frequency bands. The resulting matrices were converted to graphs, and mean degree, clustering coefficient and shortest path length was computed as a function of memory load. The results showed that brain networks of theta-, alpha-, beta-, and gamma- frequency bands were load-dependent and visual-field dependent. The networks of theta- and alpha- bands phase synchrony were most predominant in retention period for right visual field (RVF) WM than for LVF WM. Furthermore, only for RVF memory condition, brain network density of theta-band during the retention interval were linked to the delay of behavior reaction time, and the topological property of alpha-band network was negative correlation with behavior accuracy.Conclusions/significanceWe suggest that the differences in theta- and alpha- bands between LVF and RVF conditions in functional connectivity and topological properties during retention period may result in the decline of behavioral performance in RVF task.

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Reconstructions of information in visual spatial working memory degrade with memory load.

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Reconstructions of information in visual spatial working memory degrade with memory load.

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