Targets Need Their Own Personal Space: Effects of Clutter on Multiple-Target Search Accuracy

Assessing satisfaction of search in virtual mammograms for experienced and novice searchers

Purpose

Satisfaction of search (SOS) is a phenomenon where searchers are more likely to miss a lesion/target after detecting a first lesion/target. Here, we investigated SOS for masses and calcifications in virtual mammograms with experienced and novice searchers to determine the extent to which: (1) SOS affects breast lesion detection, (2) similarity between lesions impacts detection, and (3) experience impacts SOS rates.

Approach

The open virtual clinical trials framework was used to simulate the breast anatomy of patients, and up to two simulated masses and/or single-calcifications were inserted into the breast models. Experienced searchers (residents, fellows, and radiologists with breast imaging experience) and novice searchers (undergraduates who had no breast imaging experience) were instructed to search for up to two lesions (masses and calcifications) per image.

Results

2 × 2 mixed factors analysis of variances (ANOVAs) were run with: (1) single versus second lesion hit rates, (2) similar versus dissimilar second-lesion hit rates, and (3) similar versus dissimilar second-lesion response times as within-subject factors and experience as the between subject's factor. The ANOVAs demonstrated that: (1) experienced and novice searchers made a significant amount of SOS errors, (2) similarity had little impact on experienced searchers, but novice searchers were more likely to miss a dissimilar second lesion compared to when it was similar to a detected first lesion, (3) experienced and novice searchers were faster at finding similar compared to dissimilar second lesions.

Conclusions

We demonstrated that SOS is a significant cause of lesion misses in virtual mammograms and that reader experience impacts detection rates for similar compared to dissimilar abnormalities. These results suggest that experience may impact strategy and/or recognition with theoretical implications for determining why SOS occurs.

From "satisfaction of search" to "subsequent search misses": a review of multiple-target search errors across radiology and cognitive science

For over 50 years, the satisfaction of search effect has been studied within the field of radiology. Defined as a decrease in detection rates for a subsequent target when an initial target is found within the image, these multiple target errors are known to underlie errors of omission (e.g., a radiologist is more likely to miss an abnormality if another abnormality is identified). More recently, they have also been found to underlie lab-based search errors in cognitive science experiments (e.g., an observer is more likely to miss a target 'T' if a different target 'T' was detected). This phenomenon was renamed the subsequent search miss (SSM) effect in cognitive science. Here we review the SSM literature in both radiology and cognitive science and discuss: (1) the current SSM theories (i.e., satisfaction, perceptual set, and resource depletion theories), (2) the eye movement errors that underlie the SSM effect, (3) the existing efforts tested to alleviate SSM errors, and (4) the evolution of methodologies and analyses used when calculating the SSM effect. Finally, we present the attentional template theory, a novel mechanistic explanation for SSM errors, which ties together our current understanding of SSM errors and the attentional template literature.

Prospects for using visual search tasks in modern cognitive psychology

The article describes the main results of modern foreign studies with modifications of classical visual search tasks, as well as proposed classification of such modifications. The essence of visual search is to find target stimuli among the distracters, and the standard task involves finding one target stimulus, which is usually a simple object. Modifications to the standard task may include the presence of more than one target on the screen, the search for more than one type of target, and options that combine both of these modifications. Proposed modifications of the standard task allow not only to study new aspects of visual attention, but also to approach real-life tasks within laboratory studies.

Distracting Objects Induce Early Quitting in Visual Search

Task-irrelevant objects can sometimes capture attention and increase the time it takes an observer to find a target. However, less is known about how these distractors impact visual search strategies. Here, I found that salient distractors reduced rather than increased response times on target-absent trials (Experiment 1; N = 200). Combined with higher error rates on target-present trials, these results indicate that distractors can induce observers to quit search earlier than they otherwise would. These effects were replicated when target prevalence was low (Experiment 2; N = 200) and with different stimuli that elicited shallower search slopes (Experiment 3; N = 75). These results demonstrate that salient distractors can produce at least two consequences in visual search: They can capture attention, and they can cause observers to quit searching early. This novel finding has implications both for understanding visual attention and for examining distraction in real-world domains where targets are often absent, such as medical image screening.

Do target detection and target localization always go together? Extracting information from briefly presented displays

The human visual system is capable of processing an enormous amount of information in a short time. Although rapid target detection has been explored extensively, less is known about target localization. Here we used natural scenes and explored the relationship between being able to detect a target (present vs. absent) and being able to localize it. Across four presentation durations (~ 33-199 ms), participants viewed scenes taken from two superordinate categories (natural and manmade), each containing exemplars from four basic scene categories. In a two-interval forced choice task, observers were asked to detect a Gabor target inserted in one of the two scenes. This was followed by one of two different localization tasks. Participants were asked either to discriminate whether the target was on the left or the right side of the display or to click on the exact location where they had seen the target. Targets could be detected and localized at our shortest exposure duration (~ 33 ms), with a predictable improvement in performance with increasing exposure duration. We saw some evidence at this shortest duration of detection without localization, but further analyses demonstrated that these trials typically reflected coarse or imprecise localization information, rather than its complete absence. Experiment 2 replicated our main findings while exploring the effect of the level of "openness" in the scene. Our results are consistent with the notion that when we are able to extract what objects are present in a scene, we also have information about where each object is, which provides crucial guidance for our goal-directed actions.

Using Eye Movements to Understand how Security Screeners Search for Threats in X-Ray Baggage

There has been an increasing drive to understand failures in searches for weapons and explosives in X-ray baggage screening. Tracking eye movements during the search has produced new insights into the guidance of attention during the search, and the identification of targets once they are fixated. Here, we review the eye-movement literature that has emerged on this front over the last fifteen years, including a discussion of the problems that real-world searchers face when trying to detect targets that could do serious harm to people and infrastructure.

Mammography to tomosynthesis: examining the differences between two-dimensional and segmented-three-dimensional visual search

BACKGROUND

Radiological techniques for breast cancer detection are undergoing a massive technological shift-moving from mammography, a process that takes a two-dimensional (2D) image of breast tissue, to tomosynthesis, a technique that creates a segmented-three-dimensional (3D) image. There are distinct benefits of tomosynthesis over mammography with radiologists having fewer false positives and more accurate detections; yet there is a significant and meaningful disadvantage with tomosynthesis in that it takes longer to evaluate each patient. This added time can dramatically impact workflow and have negative attentional and cognitive impacts on interpretation of medical images. To better understand the nature of segmented-3D visual search and the implications for radiology, the current study looked to establish a new testing platform that could reliably examine differences between 2D and segmented-3D search.

RESULTS

In Experiment 1, both professionals (radiology residents and certified radiologists) and non-professionals (undergraduate students) were found to have fewer false positives and were more accurate in segmented-3D displays, but at the cost of taking significantly longer in search. Experiment 2 tested a second group of non-professional participants, using a background that more closely resembled a mammogram, and replicated the results of Experiment 1-search was more accurate and there were fewer false alarms in segmented 3D displays but took more time.

CONCLUSION

The results of Experiments 1 and 2 matched the performance patterns found in previous radiology studies and in the clinic, suggesting this novel experimental paradigm potentially provides a flexible and cost-effective tool that can be utilized with non-professional populations to inform relevant visual search performance. From an academic perspective, this paradigm holds promise for examining the nature of segmented-3D visual search.

Finding cancer in mammograms: if you know it's there, do you know where?

Humans can extract considerable information from scenes, even when these are presented extremely quickly. The ability of an experienced radiologist to rapidly detect an abnormality on a mammogram may build upon this general capacity. Although radiologists have been shown to be able to detect an abnormality 'above chance' at short durations, the extent to which abnormalities can be localised at brief presentations is less clear. Extending previous work, we presented radiologists with unilateral mammograms, 50% containing a mass, for 250 or 1000 ms. As the female breast varies with respect to the level of normal fibroglandular tissue, the images were categorised into high and low density (50% of each), resulting in difficult and easy searches, respectively. Participants were asked to decide whether there was an abnormality (detection) and then to locate the mass on a blank outline of the mammogram (localisation). We found both detection and localisation information for all conditions. Although there may be a dissociation between detection and localisation on a small proportion of trials, we find a number of factors that lead to the underestimation of localisation including stimulus variability, response imprecision and participant guesses. We emphasise the importance of taking these factors into account when interpreting results. The effect of density on detection and localisation highlights the importance of considering breast density in medical screening.

Perceptual similarity in visual search for multiple targets

Visual search for multiple targets can cause errors called subsequent search misses (SSM) - a decrease in accuracy at detecting a second target after a first target has been found. One of the possible explanations of SSM errors is perceptual set. After the first target has been found, the subjects become biased to find perceptually similar targets, therefore they are more likely to find perceptually similar targets and less likely to find the targets that are perceptually dissimilar. This study investigated the role of perceptual similarity in SSM errors. The search array in each trial consisted of 20 stimuli (ellipses and crosses, black and white, small and big, oriented horizontally and vertically), which could contain one, two or no targets. In case of two targets, the targets could have two, three or four shared features (in the last case the targets were identical). The error rate decreased with increasing the similarity between the targets. These results state the role of perceptual similarity and have implications for the perceptual set theory.

An individual differences approach to multiple-target visual search errors: How search errors relate to different characteristics of attention

A persistent problem in visual search is that searchers are more likely to miss a target if they have already found another in the same display. This phenomenon, the Subsequent Search Miss (SSM) effect, has remained despite being a known issue for decades. Increasingly, evidence supports a resource depletion account of SSM errors-a previously detected target consumes attentional resources leaving fewer resources available for the processing of a second target. However, "attention" is broadly defined and is composed of many different characteristics, leaving considerable uncertainty about how attention affects second-target detection. The goal of the current study was to identify which attentional characteristics (i.e., selection, limited capacity, modulation, and vigilance) related to second-target misses. The current study compared second-target misses to an attentional blink task and a vigilance task, which both have established measures that were used to operationally define each of four attentional characteristics. Second-target misses in the multiple-target search were correlated with (1) a measure of the time it took for the second target to recovery from the blink in the attentional blink task (i.e., modulation), and (2) target sensitivity (d') in the vigilance task (i.e., vigilance). Participants with longer recovery and poorer vigilance had more second-target misses in the multiple-target visual search task. The results add further support to a resource depletion account of SSM errors and highlight that worse modulation and poor vigilance reflect a deficit in attentional resources that can account for SSM errors.