Hybrid visual and memory search for scenes and objects with variable viewpoints.

In hybrid search, observers search visual arrays for any of several target types held in memory. The key finding in hybrid search is that response times (RTs) increase as a linear function of the number of items in a display (visual set size), but RTs increase linearly with the log of the memory set size. Previous experiments have shown this result for specific targets (find exactly this picture of a boot on a blank background) and for broad categorical targets (find any animal). Arguably, these are rather unnatural situations. In the real world, objects are parts of scenes and are seen from multiple viewpoints. The present experiments generalize the hybrid search findings to scenes (Experiment 1) and multiple viewpoints (Experiment 2). The results replicated the basic pattern of hybrid search results: RTs increased logarithmically with the number of scene photos/categories held in memory. Experiment 3 controls the experiment for which viewpoints were seen in an initial learning phase. The results replicate the findings of Experiment 2. Experiment 4 compares hybrid search for specific viewpoints, variable viewpoints, and categorical targets. Search difficulty increases from specific viewpoints to variable viewpoints and then to categorical targets. The results of the four experiments show the generality of logarithmic search through memory in hybrid search.

Visual search errors are persistent in a laboratory analog of the incidental finding problem.

When radiologists search for a specific target (e.g., lung cancer), they are also asked to report any other clinically significant "incidental findings" (e.g., pneumonia). These incidental findings are missed at an undesirably high rate. In an effort to understand and reduce these errors, Wolfe et al. (Cognitive Research: Principles and Implications 2:35, 2017) developed "mixed hybrid search" as a model system for incidental findings. In this task, non-expert observers memorize six targets: half of these targets are specific images (analogous to the suspected diagnosis in the clinical task). The other half are broader, categorically defined targets, like "animals" or "cars" (analogous to the less well-specified incidental findings). In subsequent search through displays for any instances of any of the targets, observers miss about one third of the categorical targets, mimicking the incidental finding problem. In the present paper, we attempted to reduce the number of errors in the mixed hybrid search task with the goal of finding methods that could be deployed in a clinical setting. In Experiments 1a and 1b, we reminded observers about the categorical targets by inserting non-search trials in which categorical targets were clearly marked. In Experiment 2, observers responded twice on each trial: once to confirm the presence or absence of the specific targets, and once to confirm the presence or absence of the categorical targets. In Experiment 3, observers were required to confirm the presence or absence of every target on every trial using a checklist procedure. Only Experiment 3 produced a marked decline in categorical target errors, but at the cost of a substantial increase in response time.

Looking ahead: When do you find the next item in foraging visual search?

Many real-world visual tasks involve searching for multiple instances of a target (e.g., picking ripe berries). What strategies do observers use when collecting items in this type of search? Do they wait to finish collecting the current item before starting to look for the next target, or do they search ahead for future targets? We utilized behavioral and eye-tracking measures to distinguish between these two possibilities in foraging search. Experiment 1 used a color wheel technique in which observers searched for T shapes among L shapes while all items independently cycled through a set of colors. Trials were abruptly terminated, and observers reported both the color and location of the next target that they intended to click. Using observers' color reports to infer target-finding times, we demonstrate that observers found the next item before the time of the click on the current target. We validated these results in Experiment 2 by recording fixation locations around the time of each click. Experiment 3 utilized a different procedure, in which all items were intermittently occluded during the trial. We then calculated a distribution of when targets were visible around the time of each click, allowing us to infer when they were most likely found. In a fourth and final experiment, observers indicated the locations of multiple future targets after the search was abruptly terminated. Together, our results provide converging evidence to demonstrate that observers can find the next target before collecting the current target and can typically forage one to two items ahead.

Perception in dynamic scenes: What is your Heider capacity?

The classic animation experiment by Heider and Simmel (1944) revealed that humans have a strong tendency to impose narrative even on displays showing interactions between simple geometric shapes. In their most famous animation with three simple shapes, observers almost inevitably interpreted them as rational agents with intentions, desires, and beliefs ("That nasty big triangle!"). Much work on dynamic scenes has identified basic visual properties that can make shapes seem animate. Here, we investigate the limits on the ability to use narrative to share information about animated scenes. We created 30 second Heider-style cartoons with 3-9 items. Item trajectories were generated automatically by a simple set of rules, but without a script. In Experiments 1 and 2, 10 observers wrote short narratives for each cartoon. Next, new observers were shown a cartoon and then presented with a narrative generated for that specific cartoon or one generated for a different cartoon having the same items. Observers rated the fit of the narrative to the cartoon on a scale from 1 (clearly does not fit) to 5 (clearly fits). Performance declined markedly when the number of items was larger than 3. Experiment 3 had observers determine if a short clip of a cartoon came from a longer clip. Experiment 4 had observers determine which of two narratives fit a cartoon. Finally, in Experiment 5, narratives always mentioned every item in a display. In all cases of matching narrative to cartoon, performance drops most dramatically between 3 and 4 items. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Event monitoring: Can we detect more than one event at a time?

A prior study by Wu and Wolfe found that the capacity for event monitoring (e.g. did an item change its state?) is more limited than for classic multiple object tracking. That limited capacity, K, could arise from either of two situations. It could be that people can detect K events simultaneously or it could be that they can successfully detect just one event at a time while monitoring K out of a total of N items. In the three different experiments of the present study, observers were asked to monitor a set of moving objects while watching for two critical events occurring in that set. Observers' performance can be well described by a model that includes an ability to detect two changes at once. Our results suggest that the capacity for event monitoring is further limited when tracking an additional event, but within the monitored set, people can detect at least two events simultaneously.

Hybrid value foraging: How the value of targets shapes human foraging behavior.

In hybrid foraging, observers search visual displays for multiple instances of multiple target types. In previous hybrid foraging experiments, although there were multiple types of target, all instances of all targets had the same value. Under such conditions, behavior was well described by the marginal value theorem (MVT). Foragers left the current "patch" for the next patch when the instantaneous rate of collection dropped below their average rate of collection. An observer's specific target selections were shaped by previous target selections. Observers were biased toward picking another instance of the same target. In the present work, observers forage for instances of four target types whose value and prevalence can vary. If value is kept constant and prevalence manipulated, participants consistently show a preference for the most common targets. Patch-leaving behavior follows MVT. When value is manipulated, observers favor more valuable targets, though individual foraging strategies become more diverse, with some observers favoring the most valuable target types very strongly, sometimes moving to the next patch without collecting any of the less valuable targets.

How did I miss that? Developing mixed hybrid visual search as a 'model system' for incidental finding errors in radiology.

In a real world search, it can be important to keep 'an eye out' for items of interest that are not the primary subject of the search. For instance, you might look for the exit sign on the freeway, but you should also respond to the armadillo crossing the road. In medicine, these items are known as "incidental findings," findings of possible clinical significance that were not the main object of search. These errors (e.g., missing a broken rib while looking for pneumonia) have medical consequences for the patient and potential legal consequences for the physician. Here we report three experiments intended to develop a 'model system' for incidental findings - a paradigm that could be used in the lab to develop strategies to reduce incidental finding errors in the clinic. All the experiments involve 'hybrid' visual search for any of several targets held in memory. In this 'mixed hybrid search task,' observers search for any of three specific targets (e.g., this rabbit, this truck, and this spoon) and three categorical targets (e.g., masks, furniture, and plants). The hypothesis is that the specific items are like the specific goals of a real world search and the categorical targets are like the less well-defined incidental findings that might be present and that should be reported. In all these experiments, varying target prevalence, number of targets, etc., the categorical targets are missed at a much higher rate than the specific targets. This paradigm shows promise as a model of the incidental finding problem.