Does Contralateral Delay Activity Reflect Working Memory Storage or the Current Focus of Spatial Attention within Visual Working Memory?

Abstract

During the retention of visual information in working memory, event-related brain potentials show a sustained negativity over posterior visual regions contralateral to the side where memorised stimuli were presented. This contralateral delay activity (CDA) is generally believed to be a neural marker of working memory storage. In two experiments, we contrasted this storage account of the CDA with the alternative hypothesis that the CDA reflects the current focus of spatial attention on a subset of memorized items set up during the most recent encoding episode. We employed a sequential loading procedure where participants memorised four task-relevant items that were presented in two successive memory displays (M1 and M2). In both experiments, CDA components were initially elicited contralateral to task-relevant items in M1. Critically, the CDA switched polarity when M2 displays appeared on the opposite side. In line with the attentional activation account, these reversed CDA components exclusively reflected the number of items that were encoded from M2 displays, irrespective of how many M1 items were already held in working memory. On trials where M1 and M2 displays were presented on the same side, and on trials where M2 displays appeared non-laterally, CDA components elicited in the interval after M2 remained sensitive to a residual trace of M1 items, indicating that some activation of previously stored items was maintained across encoding episodes. These results challenge the hypothesis that CDA amplitudes directly reflect the total number of stored objects, and suggest that the CDA is primarily sensitive to the activation of a subset of working memory representations within the current focus of spatial attention.

Unattended but actively stored: EEG dynamics reveal a dissociation between selective attention and storage in working memory

“…Here we extent these findings by showing, across two conditions, both equal CDA and different contralateral alpha power, and also equal contralateral alpha power and different CDAs at different time points within the same dataset, thus provide strong evidence for a dissociation between these two signals. Together, these findings suggest that the CDA reflects storage in WM 57 and the contralateral alpha suppression reflects allocation of attention within WM 92 and argue against a recent claim that suggested CDA reflects the current focus of attention instead of storage in WM 93 .…”

Contralateral delay activity tracks the storage of visually presented letters and words

“…The CDA is considered to be a marker of visual working memory storage (Vogel & Machizawa, 2004; McCollough, Machizawa, & Vogel, 2007; Luria, Balaban, Awh, & Vogel, 2016; but see Eimer & Kiss, 2010; Katus & Eimer, 2015; Berggren & Eimer, 2016), and so the present results fit with the possibility that participants store alphanumeric and verbal stimuli in visual working memory during change detection tasks such as the one used here. These results also fit well with fMRI studies that show recruitment of posterior parietal cortex (PPC) for both simple visual stimuli and for verbal stimuli (Todd & Marois, 2004; Majerus et al, 2011; 2014), suggesting that PPC could participate in maintaining diverse codes (Xu, 2017).…”

Interactions of emotion and anxiety on visual working memory performance

“…This alternative Bsensory recruitment^account (Awh & Jonides, 2001;Postle, 2005) proposes that visual working memory maintenance primarily occurs in modality-specific sensory areas of the brain involved in perceptual analysis, whereas prefrontal activity may reflect higher-level control processes, such as inhibition of irrelevant information. Sustained spatial attention also appears to have a strong role in augmenting memory representations, with neural markers of delay/ maintenance period activity corresponding to the current focus of attention within working memory (Berggren & Eimer, 2016;Lewis-Peacock, Drysdale, Oberauer, & Postle, 2012). Following this account, there is evidence that both threat and anxiety may impact sensory processing in a beneficial fashion.…”