Eren Gunseli

The time course of protecting a visual memory representation from perceptual interference

Cueing a remembered item during the delay of a visual memory task leads to enhanced recall of the cued item compared to when an item is not cued. This cueing benefit has been proposed to reflect attention within visual memory being shifted from a distributed mode to a focused mode, thus protecting the cued item against perceptual interference. Here we investigated the dynamics of building up this mnemonic protection against visual interference by systematically varying the stimulus onset asynchrony (SOA) between cue onset and a subsequent visual mask in an orientation memory task. Experiment 1 showed that a cue counteracted the deteriorating effect of pattern masks. Experiment 2 demonstrated that building up this protection is a continuous process that is completed in approximately half a second after cue onset. The similarities between shifting attention in perceptual and remembered space are discussed.

Is a search template an ordinary working memory? Comparing electrophysiological markers of working memory maintenance for visual search and recognition

Visual search requires the maintenance of a search template in visual working memory in order to guide attention towards the target. This raises the question whether a search template is essentially the same as a visual working memory representation used in tasks that do not require attentional guidance, or whether it is a qualitatively different representation. Two experiments tested this by comparing electrophysiological markers of visual working memory maintenance between simple recognition and search tasks. For both experiments, responses were less rapid and less accurate in search task than in simple recognition. Nevertheless, the contralateral delay activity (CDA), an index of quantity and quality of visual working memory representations, was equal across tasks. On the other hand, the late positive complex (LPC), which is sensitive to the effort invested in visual working memory maintenance, was greater for the search task than the recognition task. Additionally, when the same target cue was repeated across trials (Experiment 2), the amplitude of visual working memory markers (both CDA and LPC) decreased, demonstrating learning of the target at an equal rate for both tasks. Our results suggest that a search template is qualitatively the same as a representation used for simple recognition, but greater effort is invested in its maintenance.

Effects of search difficulty on the selection, maintenance, and learning of attentional templates

Prominent theories of attention claim that visual search is guided through attentional templates stored in working memory. Recently, the contralateral delay activity (CDA), an electrophysiological index of working memory storage, has been found to rapidly decrease when participants repeatedly search for the same target, suggesting that, with learning, the template moves out of working memory. However, this has only been investigated with pop-out search for distinct targets, for which a strong attentional template may not be necessary. More effortful search tasks might rely more on an active attentional template in working memory, leading to a slower handoff to long-term memory and thus a slower decline of the CDA. Using ERPs, we compared the rate of learning of attentional templates in pop-out and effortful search tasks. In two experiments, the rate of decrease in the CDA was the same for both search tasks. Similar results were found for a second component indexing working memory effort, the late positive complex. However, the late positive complex was also sensitive to anticipated search difficulty, as was expressed in a greater amplitude before the harder search task. We conclude that the amount of working memory effort invested in maintaining an attentional template, but not the rate of learning, depends on search difficulty.

Task-irrelevant memories rapidly gain attentional control with learning.

Although many of our perceptual biases stem from long-term, repeated exposure, current theories of visual search assume a central role for visual working memory (VWM) in guiding attention to target information. Crucially, whether a VWM representation guides attention depends on the relative priority that the memory has within VWM. Here, in a combined visual search/VWM task, we used attentional guidance by irrelevant memories to measure how long a target representation remains prioritized in VWM when observers repeatedly search for the same target. Irrelevant memories started guiding attention already when the target was repeated once, indicating that the target representation rapidly lost priority within VWM as it moved to long-term memory. By showing that training can lead to interference from irrelevant memories, the findings resolve a long-standing paradox on why VWM appears central to, yet at the same time not sufficient nor necessary for attentional guidance.

Local and interregional alpha EEG dynamics dissociate between memory for search and memory for recognition

ABSTRACT Attention during visual search is thought to be guided by an active visual working memory (VWM) representation of the search target. We tested the hypothesis that a VWM representation used for searching a target among competing information (a “search template”) is distinct from VWM representations used for simple recognition tasks, without competition. We analyzed EEG from 20 human participants while they performed three different VWM‐based visual detection tasks. All tasks started with identical lateralized VWM cues, but differed with respect to the presence and nature of competing distractors during the target display at test, where participants performed a simple recognition task without distractors, or visual search in pop‐out (distinct) and serial (non‐distinct) search displays. Performance was worst for non‐distinct search, and best for simple recognition. During the one second delay period between cue and test, we observed robust suppression of EEG dynamics in the alpha (8–14 Hz) band over parieto‐occipital sites contralateral to the relevant VWM item, both in terms of local power as well as interregional phase synchrony within a posterior‐parietal network. Importantly, these lateralization dynamics were more strongly expressed prior to search compared to simple recognition. Furthermore, before the VWM cue, alpha phase synchrony between prefrontal and mid‐posterior‐parietal sites was strongest for non‐distinct search, reflecting enhanced anticipatory control prior to VWM encoding. Directional connectivity analyses confirmed this effect to be in an anterior‐to‐posterior direction. Together, these results provide evidence for frontally mediated top‐down control of VWM in preparation of visual search. HighlightsWe compared visual working memory prior to search versus simple recognition.Lateralized memoranda elicited robust contralateral alpha (8–14 Hz) suppression.Lateralized alpha suppression was stronger when memory was needed for visual search.Pre‐stimulus long‐range alpha connectivity was similarly modulated by task demands.We find that the alpha‐band supports increased top‐down control of search templates.

Erratum to: The reliability of retro-cues determines the fate of noncued visual working memory representations.

1. The validity ratios of two studies were erroneously swapped.We reported a validity ratio of 50% for Landman, Spekreijse, and Lamme (2003) and 66.6% for Rerko and Oberauer (2013), where we intended 66.6% for Landman et al. (2003) and 50% for Rerko and Oberauer (2013). 2. For the study of Matsukura, Luck, and Vecera (2007), we reported a validity ratio of 75%, but this was based on an inconsistency in our calculations. A more consistent calculation yields 73.3% instead.

The Loss of Information from Visual Working Memory depends on Retro-Cue Reliability.

Retrospectively cueing an item retained in visual working memory during maintenance is known to improve its retention. However, literature has provided conflicting results regarding the costs of such retro-cues for non-cued items, which has led to a variety of theories on the role of cueing in visual working memory. We hypothesized that the differences in the reliability of retro-cues across studies might be a factor underlying conflicting results. We predicted that the more reliable the cues, the larger the costs for non-cued items. Participants performed a working memory task while electroencephalography (EEG) was recorded. Retro-cues indicated which of several items was most likely to be tested. We manipulated, between blocks, the ratio of trials on which the cue was valid vs. invalid. In addition to memory performance, we investigated the contralateral delay activity (CDA) in the EEG, which is claimed to index visual working memory maintenance. We also applied multivariate pattern analysis (MVPA) in the frequency domain to decode the location of the cued item. Reconciling previous contradictory findings, costs of invalid retro-cueing on recall performance (i.e. probability and precision estimates) were found only for highly reliable cues. Nevertheless, benefits of valid cueing were present for both reliabilities, though larger for highly reliable cues. Moreover, the CDA emerged only after a highly reliable cue. Finally, decoding accuracy was above chance level in the high alpha band (i.e. 10-12 Hz) following a retro-cue and was larger for highly reliable cues. Our results suggest that non-cued representations are removed from working memory only if the retro-cue reliability is high. Moreover, the presence of valid cueing benefits in the absence of invalid cueing costs suggests that an item in working memory can be prioritized without reallocation of memory resources. Meeting abstract presented at VSS 2015.