Why is information displaced from visual working memory during visual search?

Research has shown that performing visual search while maintaining representations in visual working memory displaces up to one object's worth of information from memory. This memory displacement has previously been attributed to a nonspecific disruption of the memory representation by the mere presentation of the visual search array, and the goal of the present study was to determine whether it instead reflects the use of visual working memory in the actual search process. The first hypothesis tested was that working memory displacement occurs because observers preemptively discard about an object's worth of information from visual working memory in anticipation of performing visual search. Second, we tested the hypothesis that on target absent trials no information is displaced from visual working memory because no target is entered into memory when search is completed. Finally, we tested whether visual working memory displacement is due to the need to select a response to the search array. The findings rule out these alternative explanations. The present study supports the hypothesis that change-detection performance is impaired when a search array appears during the retention interval due to nonspecific disruption or masking.     

Do object refixations during scene viewing indicate rehearsal in visual working memory?

Do refixations serve a rehearsal function in visual working memory (VWM)? We analyzed refixations from observers freely viewing multiobject scenes. An eyetracker was used to limit the viewing of a scene to a specified number of objects fixated after the target (intervening objects), followed by a four-alternative forced choice recognition test. Results showed that the probability of target refixation increased with the number of fixated intervening objects, and these refixations produced a 16% accuracy benefit over the first five intervening-object conditions. Additionally, refixations most frequently occurred after fixations on only one to two other objects, regardless of the intervening-object condition. These behaviors could not be explained by random or minimally constrained computational models; a VWM component was required to completely describe these data. We explain these findings in terms of a monitor–refixate rehearsal system: The activations of object representations in VWM are monitored, with refixations occurring when these activations decrease suddenly.     

Is the binding of visual features in working memory resource-demanding?

The episodic buffer component of working memory is assumed to play a role in the binding of features into chunks. A series of experiments compared memory for arrays of colors or shapes with memory for bound combinations of these features. Demanding concurrent verbal tasks were used to investigate the role of general attentional processes, producing load effects that were no greater on memory for feature combinations than for the features themselves. However, the binding condition was significantly less accurate with sequential rather than simultaneous presentation, especially for items earlier in the sequence. The findings are interpreted as evidence of a relatively automatic but fragile visual feature binding mechanism in working memory. Implications for the concept of an episodic buffer are discussed.     

Emotional devaluation of distracting patterns and faces: a consequence of attentional inhibition during visual search?

Visual search has been studied extensively, yet little is known about how its constituent processes affect subsequent emotional evaluation of searched-for and searched-through items. In 3 experiments, the authors asked observers to locate a colored pattern or tinted face in an array of other patterns or faces. Shortly thereafter, either the target or a distractor was rated on an emotional scale (patterns, cheerfulness; faces, trustworthiness). In general, distractors were rated more negatively than targets. Moreover, distractors presented near the target during search were rated significantly more negatively than those presented far from the target. Target-distractor proximity affected distractor ratings following both simple-feature and difficult-conjunction search, even when items appeared at different locations during evaluation than during search and when faces previously tinted during search were presented in grayscale at evaluation. An attentional inhibition account is offered to explain these effects of attention on emotional evaluation.     

Do binding deficits account for age-related decline in visual working memory?

Remembering visual material, such as objects, faces, and spatial locations, over a short period of time (seconds) becomes more difficult as we age. We investigated whether these deficits could be explained by a simple reduction in visual working memory capacity or by an impairment in one's ability to form or maintain appropriate associations among pieces of related information. In three experiments, we used recognition and recall tests to address the efficacy with which older adults can create bound object representations by varying the number of features of each object that had to be remembered for a subsequent memory test. Results demonstrated that whereas older adults exhibited reduced memory capacity as compared with that of younger adults, both groups stored integrated object representations in visual working memory. These results are contrasted with other work that suggests that age-related memory decline is due, at least in part, to associative deficits.     

Does high memory load kick task-irrelevant information out of visual working memory?

The limited capacity of visual working memory (VWM) requires the existence of an efficient information selection mechanism. While it has been shown that under low VWM load, an irrelevant simple feature can be processed, its fate under high load (e.g., six objects) remains unclear. We explored this issue by probing the “irrelevant-change distracting effect,” in which the change of a stored irrelevant feature affects performance. Simple colored shapes were used as stimuli, with color as the target. Using a whole-probe method (presenting six objects in both the memory and test arrays), in Experiment 1 we found that a change to one of the six shapes led to a significant distracting effect. Using a partial-probe method (presenting the probe either at the screen center or at a location selected from the memory array), in Experiment 2 we showed the distracting effect again. These results suggest that irrelevant simple features can be stored into VWM, regardless of memory load.     

What do eye movements reveal about the role of memory in visual search?

Horowitz and Wolfe (1998, 2003) have challenged the view that serial visual search involves memory processes that keep track of already inspected locations. The present study used a search paradigm similar to Horowitz and Wolfe's (1998), comparing a standard static search condition with a dynamic condition in which display elements changed locations randomly every 111 ms. In addition to measuring search reaction times, observers' eye movements were recorded. For target-present trials, the search rates were near-identical in the two search conditions, replicating Horowitz and Wolfe's findings. However, the number of fixations and saccade amplitude were larger in the static than in the dynamic condition, whereas fixation duration and the latency of the first saccade were longer in the dynamic condition. These results indicate that an active, memory-guided search strategy was adopted in the static condition, and a passive “sit-and-wait” strategy in the dynamic condition.     

What do eye movements reveal about the role of memory in visual search?

Horowitz and Wolfe (1998, 2003) have challenged the view that serial visual search involves memory processes that keep track of already inspected locations. The present study used a search paradigm similar to Horowitz and Wolfe's (1998), comparing a standard static search condition with a dynamic condition in which display elements changed locations randomly every 111 ms. In addition to measuring search reaction times, observers' eye movements were recorded. For target-present trials, the search rates were near-identical in the two search conditions, replicating Horowitz and Wolfe's findings. However, the number of fixations and saccade amplitude were larger in the static than in the dynamic condition, whereas fixation duration and the latency of the first saccade were longer in the dynamic condition. These results indicate that an active, memory-guided search strategy was adopted in the static condition, and a passive “sit-and-wait” strategy in the dynamic condition.     

Are attentional dwell times inconsistent with serial visual search?

Duncan, Ward, and Shapiro (1994) estimated that attention must remain focused on an object for several hundred milliseconds before being shifted to another object, and they referred to this period as theattentional dwell time. An important implication of these long estimates of the dwell time for models of visual search is that the search process must not involve an item-by-item serial scanning mechanism. If it did, then searching through an array of items would require enormous amounts of time, which—based on data from visual search experiments—it does not. The present report, however, provides evidence that the long estimates of attentional dwell time were caused, at least in part, by the use of masked targets. Implications of these variable estimates of the attentional dwell time for models of visual search are discussed.     

Spatial working memory maintenance: Does attention play a role? A visual search study

Recent studies have proposed that a common mechanism may underlie spatial attention and spatial working memory. One proposal is that spatial working memory is maintained by attention-based rehearsal [Awh, E., Jonides, J., & Reuter-Lorenz, P. A. (1998). Rehearsal in spatial working memory. Journal of Experimental Psychology: Human Perception and Performance, 24(3), 780-790], and so a spatial attention shift during the retention interval of a spatial location should impair its memory performance. In the present study, participants engaged in single-item, parallel or serial search tasks while remembering a spatial location. Although memory tended to bias all searches, the need for an attentional shift during the retention interval impaired memory performance only in single-item search, but not in other searches. These findings suggest that previous evidence for the attention-based rehearsal account does not generalize to visual search. Results are discussed with regard to the relationship between spatial attention and spatial working memory.     

Were you paying attention to where you looked? The role of executive working memory in visual search

Recent evidence has indicated that performing a working memory task that loads executive working memory leads to less efficient visual search (Han & Kim, 2004). We explored the role that executive functioning plays in visual search by examining the pattern of eye movements while participants performed a search task with or without a secondary executive working memory task. Results indicate that executive functioning plays two roles in visual search: the identification of objects and the control of the disengagement of attention.     

Do multielement visual tracking and visual search draw continuously on the same visual attention resources?

Multielement visual tracking and visual search are 2 tasks that are held to require visual-spatial attention. The authors used the attentional operating characteristic (AOC) method to determine whether both tasks draw continuously on the same attentional resource (i.e., whether the 2 tasks are mutually exclusive). The authors found that observers can search and track within the same trial significantly better than would be predicted if the 2 tasks were mutually exclusive. In fact, the AOC for tracking and search is similar to that for tracking and auditory monitoring. The results of additional experiments support an attention-switching account for this high level of dual-task performance in which a single attentional resource is efficiently switched between the tracking and search. The results provide important constraints for architectures of visual selective attention and the mechanisms of multielement tracking.     

When do spatial and visual working memory interact?

This study examined how spatial working memory and visual (object) working memory interact, focusing on two related questions: First, can these systems function independently from one another? Second, under what conditions do they operate together? In a dual-task paradigm, participants attempted to remember locations in a spatial working memory task and colored objects in a visual working memory task. Memory for the locations and objects was subject to independent working memory storage limits, which indicates that spatial and visual working memory can function independently from one another. However, additional experiments revealed that spatial working memory and visual working memory interact in three memory contexts: when retaining (1) shapes, (2) integrated color-shape objects, and (3) colored objects at specific locations. These results suggest that spatial working memory is needed to bind colors and shapes into integrated object representations in visual working memory. Further, this study reveals a set of conditions in which spatial and visual working memory can be isolated from one another.     

Do young chimpanzees have extraordinary working memory?

Do chimpanzees have better spatial working memory than humans? In a previous report, a juvenile chimpanzee outperformed 3 university students on memory for briefly displayed digits in a spatial array (Inoue & Matsuzawa, 2007). The authors described these abilities as extraordinary and likened the chimpanzee's performance to eidetic memory. However, the chimpanzee received extensive practice on a non-time-pressured version of the task; the human subjects received none. Here we report that, after adequate practice, 2 university students substantially outperformed the chimpanzee. There is no evidence for a superior or qualitatively different spatial memory system in chimpanzees.     

How is the visual working memory load of driver influenced by information density of traffic signs?

The rapid development of urban roads has resulted in an increase in the amount of information that needs to be displayed on traffic signs. The overloading of information on traffic signs may increase drivers’ visual cognition burden and cause driving errors. It could be an important factor affecting driving safety and result in accidents. To enable drivers to cognize traffic signs, the information density that they could endure under reasonable workload levels should be determined. In this study, we designed and implemented trials to analyze drivers’ visual working memory load (VWML) caused by different information densities (including stimulus intensity (SI) and interval time of stimulus (IS)) of traffic signs. Twenty-four paid participants (12 females) with a mean age of 23.38 years (SD = 1.38) participated in laboratory simulation trials based on the memory retrieval approach. Subjective ratings (rating scale mental effort (RSME)), and performance measurement based on reaction time and accuracy of information-matching task were measured to reflect drivers’ VWML at different information densities. The results show that information density is an important factor affecting drivers’ VWML. The following are the significant observations of the study: (1) The subjective ratings on mental effort increased with increase in the SI. Meanwhile, it first decreased and then increased with increase in the IS. (2) The response accuracy results show that a high accuracy (≥0.7) was achieved by drivers in an IS of 15 s when the SI was at most 14.16 bit/m². Correspondingly, the drivers underwent less mental workload as a result of their better short-term memory characteristic. (3) The mean reaction time was over 1800 ms when the SI was over 14.16 bit/m². This indicated a reduction in the information-processing capability of the drivers. The results indicate that cognition of information of unreasonable density on traffic signs would increase drivers’ VWML. This would, in turn, result in an increase in their reaction time and decrease in accuracy. The threshold of information density was also determined through the experiment. It would satisfy the information demand of drivers and prevent information redundancy. The results contribute to an understanding of drivers’ VWML while cognizing traffic signs with different information densities and provide safety, effectiveness, and information continuity considerations for the design and setting of traffic signs.     

Does working memory training promote the use of strategies on untrained working memory tasks?

Adaptive computerized training has been associated with significant enhancements in untrained working memory tasks, but the nature of the cognitive changes that underpin these improvements are not yet fully understood. Here, we investigate the possibility that training stimulates the use of memory-related strategies. In a randomized controlled trial, participants completed four tests of working memory before receiving adaptive working memory training, nonadaptive working memory training with low memory loads, or no training. Open-ended interviews about strategy use were conducted after the administration of untrained working memory tasks at two time points. Those in the adaptive and nonadaptive groups completed the assessments before (T1) and after (T2) 10 training sessions. The no-training group completed the same set of tasks at T1 and T2, without any training between assessment points. Adaptive training was associated with selective improvements in untrained tests of working memory, accompanied by a significant increase in the use of a grouping strategy for visuospatial short-term memory and verbal working memory tasks. These results indicate that training-related improvements in working memory may be mediated by implicit and spontaneous changes in the use of strategies to subsegment sequences of information into groups for recall when the tasks used at test overlap with those used during training.     

Life-span development of visual working memory: when is feature binding difficult?

We asked whether the ability to keep in working memory the binding between a visual object and its spatial location changes with development across the life span more than memory for item information. Paired arrays of colored squares were identical or differed in the color of one square, and in the latter case, the changed color was unique on that trial (item change) or was duplicated elsewhere in the array (color-location binding change). Children (8-10 and 11-12 years old) and older adults (65-85 years old) showed deficits relative to young adults. These were only partly simulated by dividing attention in young adults. The older adults had an additional deficiency, specifically in binding information, which was evident only when item- and binding-change trials were mixed together. In that situation, the older adults often overlooked the more subtle, binding-type changes. Some working memory processes related to binding undergo life-span development in an inverted-U shape, whereas other, bias- and salience-related processes that influence the use of binding information seem to develop monotonically.     

Do gains in working memory capacity explain the written self-disclosure effect?

Klein and Boals (2001) concluded that expressive writing about negative life events improves health by reducing intrusive thoughts, as measured by the Impact of Events Scale (IES), and thus freeing working memory (WM) capacity. We replicated their WM gain and rejected the possibility that it reflected task practice alone. We extended their work by showing that such WM effects and reductions in self-reported health symptoms can be observed within a short time frame of a week in a normal population of college students and can occur without reductions in IES scores. Two alternative explanations are discussed of how WM gains can be observed in the written self-disclosure effect without reductions in the frequency of intrusive thoughts and avoidance attempts.