Mathias S. Fleck

Rare Targets Are Rarely Missed in Correctable Search

Failing to find a tumor in an x-ray scan or a gun in an airport baggage screening can have dire consequences, making it fundamentally important to elucidate the mechanisms that hinder performance in such visual searches. Recent laboratory work has indicated that low target prevalence can lead to disturbingly high miss rates in visual search. Here, however, we demonstrate that misses in low-prevalence searches can be readily abated. When targets are rarely present, observers adapt by responding more quickly, and miss rates are high. Critically, though, these misses are often due to response-execution errors, not perceptual or identification errors: Observers know a target was present, but just respond too quickly. When provided an opportunity to correct their last response, observers can catch their mistakes. Thus, low target prevalence may not be a generalizable cause of high miss rates in visual search.

Generalized "Satisfaction of Search": Adverse Influences on Dual-Target Search Accuracy

The successful detection of a target in a radiological search can reduce the detectability of a second target, a phenomenon termed satisfaction of search (SOS). Given the potential consequences, here we investigate the generality of SOS with the goal of simultaneously informing radiology, cognitive psychology, and nonmedical searches such as airport luggage screening. Ten experiments utilizing nonmedical searches and untrained searchers suggest that SOS is affected by a diverse array of factors, including (1) the relative frequency of different target types, (2) external pressures (reward and time), and (3) expectations about the number of targets present. Collectively, these experiments indicate that SOS arises when searchers have a biased expectation about the low likelihood of specific targets or events, and when they are under pressure to perform efficiently. This first demonstration of SOS outside of radiology implicates a general heuristic applicable to many kinds of searches. In an example like airport luggage screening, the current data suggest that the detection of an easy-to-spot target (e.g., a water bottle) might reduce detection of a hard-to-spot target (e.g., a box cutter).

Staying in bounds: Contextual constraints on object-file coherence

Coherent visual perception necessitates the ability to track distinct objects as the same entities over time and motion. Calculations of such object persistence appear to be fairly automatic and constrained by specific rules. We explore the nature of object persistence here within the object-file framework; object files are mid-level visual representations that track entities over time and motion as the same persisting objects and store and update information about the objects. We present three new findings. First, objects files are constrained by the principle of “boundedness”; persisting entities should maintain a single closed contour. Second, object files are constrained by the principle of “containment”; all the parts and properties of a persisting object should reside within, and be connected to, the object itself. Third, object files are sensitive to the context in which an object appears; the very same physical entity that can instantiate object-file formation in one experimental context cannot in another. This contextual influence demonstrates for the first time that object files are sensitive to more than just the physical properties contained within any given visual display.

Reducing Satisfaction of Search Errors in Visual Search

Several occupations rely upon the ability to accurately and efficiently perform visual search. For example, radiologists must successfully identify abnormalities, and airport luggage screeners must recognize threatening items. By investigating various aspects of such searches, psychological research can reveal ways to improve search performance. We (Fleck, Samei, & Mitroff, in press) have recently focused on one specific influence that had previously been explored almost exclusively within the study of radiology: Satisfaction of Search (SOS), wherein the successful detection of one target can reduce detection of a second target in the same search array. To eliminate SOS errors, we must delineate the sources of the errors. Combined with our prior work, here we examine the specific roles of target heterogeneity and the decision-making component of target-distractor discrimination (i.e., how easy it is to determine whether a stimulus is a target or a distractor). In the current experiments, subjects searched arrays of line-drawn objects for targets of two different categories (tools and bottles) amongst several categories of distractor objects. On any given trial, there could be no targets, one target (either a tool or bottle), or two targets (both a tool and a bottle). The relative occurrence of these trial types varied across experiments. Compared to previous experiments that employed homogeneous targets and that required effortful evaluation to discriminate targets from distractors, the SOS effect was reduced here. That is, search accuracy for easily discriminable, heterogeneous objects was no worse for dual-target trials than for single-target trials. These results suggest that target heterogeneity and target-distractor discriminability may both play key roles in multiple target search accuracy.