Tal Makovski

Orienting Attention in Visual Working Memory Reduces Interference From Memory Probes

Given a changing visual environment, and the limited capacity of visual working memory (VWM), the contents of VWM must be in constant flux. Using a change detection task, the authors show that VWM is subject to obligatory updating in the face of new information. Change detection performance is enhanced when the item that may change is retrospectively cued 1 s after memory encoding and 0.5 s before testing. The retro-cue benefit cannot be explained by memory decay or by a reduction in interference from other items held in VWM. Rather, orienting attention to a single memory item makes VWM more resistant to interference from the test probe. The authors conclude that the content of VWM is volatile unless it receives focused attention, and that the standard change detection task underestimates VWM capacity.

Distributing versus focusing attention in visual short-term memory

Visual short-term memory (VSTM) is traditionally considered a robust form of visual memory resistant to interference from subsequent visual input. This study shows that the robustness of VSTM depends on the way attention is allocated in VSTM. When attention is distributed across multiple memory items, VSTM for these items is vulnerable to interference from subsequent input, including passively viewed images and the postchange testing displays. Yet attention can readjust its focus in VSTM on the basis of an attentional orienting cue presented long after encoding. When attention is oriented to a particular memorized item, the memory is resistant to subsequent interference. This effect, however, is eliminated when the subset of items demanding focal attention exceeds one, suggesting that orienting attention in VSTM is less flexible than orienting attention in perception. We propose that the robustness of VSTM is influenced by whether attention is focused or distributed in VSTM.

Proactive interference from items previously stored in visual working memory.

This study investigates the fate of information that was previously stored in visual working memory but that is no longer needed. Previous research has found inconsistent results, with some showing effective release of irrelevant information and others showing proactive interference. Using change detection tasks of colors or shapes, we show that participants tend to falsely classify a changed item as “no change” if it matches one of the memory items on the preceding trial. The interference is spatially specific: Memory for the preceding trial interferes more if it matches the feature value and the location of a test item than if it does not. Interference results from retaining information in visual working memory, since it is absent when items on the preceding trials are passively viewed, or are attended but not memorized. We conclude that people cannot fully eliminate unwanted visual information from current working memory tasks.

Feature binding in attentive tracking of distinct objects

To what degree can attentive tracking of objects’ motion benefit from increased distinctiveness in the objects’ surface features? To address this question, we asked observers to track four moving digits among a total of eight moving digits. By varying the distinctiveness of the digits’ colour and identity, we found that tracking performance improved when the eight objects were all distinct in colour, digit identity, or both, compared to when the eight objects were identical. However, when the eight objects were distinct in a combination of colour and digit but targets and nontargets shared colour or digit identity, performance enhancement was not observed. Four follow-up experiments extended the range of the feature dimensions generating the effect and ruled out alternative strategic accounts. We conclude that surface features can be used to enhance tracking performance. This enhancement is feature based, revealing a limited degree of feature binding in attentive tracking.

Interference from filled delays on visual change detection.

Failure to detect changes to salient visual input across a brief interval has popularized the use of change detection, a paradigm that plays important roles in recent studies of visual perception, short-term memory, and consciousness. Much research has focused on the nature of visual representation for the pre- and postchange displays, yet little is known about how visual change detection is interfered with by events inserted between the pre- and postchange displays. To address this question, we tested change detection of colors, spatial locations, and natural scenes, when the interval between changes was (1) blank, (2) filled with a visual scene, or (3) filled with an auditory word. Participants were asked to either ignore the filled visual or auditory event or attend to it by categorizing it as animate or inanimate. Results showed that the ability to detect visual changes was dramatically impaired by attending to a secondary task during the delay. This interference was significant for auditory as well as for visual interfering events and was invariant to the complexity of the prechange displays. Passive listening produced no interference, whereas passive viewing produced small but significant interference. We conclude that visual change detection relies significantly on central, amodal attention.

Method matters: systematic effects of testing procedure on visual working memory sensitivity.

Visual working memory (WM) is traditionally considered a robust form of visual representation that survives changes in object motion, observers position, and other visual transients. This article presents data that are inconsistent with the traditional view. We show that memory sensitivity is dramatically influenced by small variations in the testing procedure, supporting the idea that representations in visual WM are susceptible to interference from testing. In the study, participants were shown an array of colors to remember. After a short retention interval, memory for one of the items was tested with either a same-different task or a 2-alternative-forced-choice (2AFC) task. Memory sensitivity was much lower in the 2AFC task than in the same-different task. This difference was found regardless of encoding similarity or of whether visual WM required a fine or coarse memory resolution. The 2AFC disadvantage was reduced when participants were informed shortly before testing which item would be probed. The 2AFC disadvantage diminished in perceptual tasks and was not found in tasks probing visual long-term memory. These results support memory models that acknowledge the labile nature of visual WM and have implications for the format of visual WM and its assessment.

Contextual cost: When a visual-search target is not where it should be

Visual search is often facilitated when the search display occasionally repeats, revealing a contextual-cueing effect. According to the associative-learning account, contextual cueing arises from associating the display configuration with the target location. However, recent findings emphasizing the importance of local context near the target have given rise to the possibility that low-level repetition priming may account for the contextual-cueing effect. This study distinguishes associative learning from local repetition priming by testing whether search is directed toward a targets expected location, even when the target is relocated. After participants searched for a T among Ls in displays that repeated 24 times, they completed a transfer session where the target was relocated locally to a previously blank location (Experiment 1) or to an adjacent distractor location (Experiment 2). Results revealed that contextual cueing decreased as the target appeared farther away from its expected location, ultimately resulting in a contextual cost when the target swapped locations with a local distractor. We conclude that target predictability is a key factor in contextual cueing.

Attention dependency in implicit learning of repeated search context.

How much attention is needed to produce implicit learning? Previous studies have found inconsistent results, with some implicit learning tasks requiring virtually no attention while others rely on attention. In this study we examine the degree of attentional dependency in implicit learning of repeated visual search context. Observers searched for a target among distractors that were either highly similar to the target or dissimilar to the target. We found that the size of contextual cueing was comparable from repetition of the two types of distractors, even though attention dwelled much longer on distractors highly similar to the target. We suggest that beyond a minimal amount, further increase in attentional dwell time does not contribute significantly to implicit learning of repeated search context.

Are multiple visual short-term memory storages necessary to explain the retro-cue effect?

Recent research has shown that change detection performance is enhanced when, during the retention interval, attention is cued to the location of the upcoming test item. This retro-cue advantage has led some researchers to suggest that visual short-term memory (VSTM) is divided into a durable, limited-capacity storage and a more fragile, high-capacity storage. Consequently, performance is poor on the no-cue trials because fragile VSTM is overwritten by the test display and only durable VSTM is accessible under these conditions. In contrast, performance is improved in the retro-cue condition because attention keeps fragile VSTM accessible. The aim of the present study was to test the assumptions underlying this two-storage account. Participants were asked to encode an array of colors for a change detection task involving no-cue and retro-cue trials. A retro-cue advantage was found even when the cue was presented after a visual (Experiment 1) or a central (Experiment 2) interference. Furthermore, the magnitude of the interference was comparable between the no-cue and retro-cue trials. These data undermine the main empirical support for the two-storage account and suggest that the presence of a retro-cue benefit cannot be used to differentiate between different VSTM storages.

Visual Learning in Multiple-Object Tracking

Background Tracking moving objects in space is important for the maintenance of spatiotemporal continuity in everyday visual tasks. In the laboratory, this ability is tested using the Multiple Object Tracking (MOT) task, where participants track a subset of moving objects with attention over an extended period of time. The ability to track multiple objects with attention is severely limited. Recent research has shown that this ability may improve with extensive practice (e.g., from action videogame playing). However, whether tracking also improves in a short training session with repeated trajectories has rarely been investigated. In this study we examine the role of visual learning in multiple-object tracking and characterize how varieties of attention interact with visual learning. Methodology/Principal Findings Participants first conducted attentive tracking on trials with repeated motion trajectories for a short session. In a transfer phase we used the same motion trajectories but changed the role of tracking targets and nontargets. We found that compared with novel trials, tracking was enhanced only when the target subset was the same as that used during training. Learning did not transfer when the previously trained targets and nontargets switched roles or mixed up. However, learning was not specific to the trained temporal order as it transferred to trials where the motion was played backwards. Conclusions/Significance These findings suggest that a demanding task of tracking multiple objects can benefit from learning of repeated motion trajectories. Such learning potentially facilitates tracking in natural vision, although learning is largely confined to the trajectories of attended objects. Furthermore, we showed that learning in attentive tracking relies on relational coding of all target trajectories. Surprisingly, learning was not specific to the trained temporal context, probably because observers have learned motion paths of each trajectory independently of the exact temporal order.