Activated long-term memory and visual working memory during hybrid visual search: Effects on target memory search and distractor memory.

In hybrid visual search, observers must maintain multiple target templates and subsequently search for any one of those targets. If the number of potential target templates exceeds visual working memory (VWM) capacity, then the target templates are assumed to be maintained in activated long-term memory (aLTM). Observers must search the array for potential targets (visual search), as well as search through memory (target memory search). Increasing the target memory set size reduces accuracy, increases search response times (RT), and increases dwell time on distractors. However, the extent of observers' memory for distractors during hybrid search is largely unknown. In the current study, the impact of hybrid search on target memory search (measured by dwell time on distractors, false alarms, and misses) and distractor memory (measured by distractor revisits and recognition memory of recently viewed distractors) was measured. Specifically, we aimed to better understand how changes in behavior during hybrid search impacts distractor memory. Increased target memory set size led to an increase in search RTs, distractor dwell times, false alarms, and target identification misses. Increasing target memory set size increased revisits to distractors, suggesting impaired distractor location memory, but had no effect on a two-alternative forced-choice (2AFC) distractor recognition memory test presented during the search trial. The results from the current study suggest a lack of interference between memory stores maintaining target template representations (aLTM) and distractor information (VWM). Loading aLTM with more target templates does not impact VWM for distracting information.

Differences in the duration of the attentional blink when viewing nature vs. urban scenes.

The current study examined how viewing nature vs. urban scenes impacts the duration of the attentional blink. Nature scenes produce a broader allocation of attention, allowing attention to spread and reduce the ability to disengage attention. Urban scenes produce a narrowed allocation of attention, allowing efficient encoding of relevant information, inhibition of irrelevant information and a speedier disengagement of attention. Participants viewed a rapid serial visual presentation (RSVP) of either nature or urban scenes. For both scene categories, an attentional blink was evident by reduced accuracy for reporting a second target that occurred two or three scenes after an accurately reported first target. However, the duration of the attentional blink was reduced for urban scenes compared with nature scenes. A peripheral target detection task confirmed a difference in the allocation of attention between scene categories. The peripheral targets were better detected for nature scenes, suggesting that participants have a broader spread of attention for nature scenes, even in an RSVP task. The shorter duration of the attentional blink for urban scenes was consistent across four experiments with small and large sets of urban and nature scenes. Therefore, urban scenes reliably reduce the attentional blink duration compared with nature scenes, and this could be attributed to a narrowed attention allocation that allows speedier disengagement of attention in an RSVP.

Behavioral and electrophysiological evidence for the flexible recruitment of feature- and object-based processing in visual working memory comparison.

Previous research is inconclusive on when visual working memory (VWM) can be object-based or feature-based. Prior event-related potential (ERP) studies using change detection tasks have found that amplitudes of the N200-an ERP index of VWM comparison- are sensitive to changes in both relevant and irrelevant features, suggesting a bias toward object-based processing. To test whether VWM comparison processing can operate in a feature-based manner, we aimed to create circumstances that would support feature-based processing by: 1) using a strong task-relevance manipulation, and 2) repeating features within a display. Participants completed two blocks of a change detection task for four-item displays in which they were told to respond to color changes (task relevant) but not shape changes (task irrelevant). The first block contained only task-relevant changes to create a strong task-relevance manipulation. In the second block, both relevant and irrelevant changes were present. In both blocks, half of the arrays contained within-display feature repetitions (e.g. two items of the same color or shape). We found that during the second block, N200 amplitudes were sensitive to task-relevant but not irrelevant features regardless of repetition status, consistent with feature-based processing. However, analyses of behavioral data and N200 latencies suggested that object-based processing was occurring at some stages of VWM processing on task-irrelevant feature change trials. In particular, task-irrelevant changes may be processed after no task-relevant feature change is revealed. Overall, the results from the current study suggest that the VWM processing is flexible and can be either object- or feature-based.