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Cognitive studies may have implications for aviation security
By PATRICIA DONOVAN
Contributing Editor
Screeners at airport security checkpoints perform an important task in which they search for objects that belong to threat categories in complex X-ray images. New research by cognitive psychologists at UB and Georgia State University explores the cognitive processes that underlie screening, suggests limits on those processes and has implications for the training and evaluation of screeners in the field.
The findings were published in the article "Specific-Token Effects in Screening Tasks: Possible Implications for Aviation Security" in the November-December issue of the American Psychological Association's Journal of Experimental Psychology: Learning, Memory and Cognition (Vol. 31, No. 6) and in the article "Visual Search and the Collapse of Categorization," in the November-December issue of the APA's Journal of Experimental Psychology: General (Vol. 134, No. 4).
The studies were conducted with grant support from the Federal Aviation Administration by J. David Smith in UB's Department of Psychology and Center for Cognitive Science and his colleagues Joshua Redford, Lauren Gent, David Washburn, and Lauren Taglialatela at UB and Georgia State University.
The problem addressed by the research, Smith says, "is that screeners must be able to bring 'category-level' knowledge to their search for targets. That is, they must search for guns and knives generally, not for specific Beretta guns or Bowie knives they have been trained to recognize. Yet it has been unknown how the processes of categorization stand up to visual complexity or why they fail facing it. We filled this research gap by creating a visual-search and categorization paradigm in which participants searched for members of target categories in complex displays."
In the studies reported in the Journal of Experimental Psychology: General, the researchers found that participants had surprising difficulty detecting category targets in complex visual displays, despite intensive category training and even when the target was completely unobscured. In fact, even a little visual complexity sharply reduced the number of targets successfully identified.
In the studies reported in the Journal of Experimental Psychology: Learning, Memory, and Cognition, the researchers let the same targets repeat in visual displays from time to time so that participant screeners could build up familiarity with them. Under these conditions, Smith says, "We observed a 'heartbeat' in detection performance—it improved while target images repeated but dropped sharply when unfamiliar targets from the same categories appeared. This reliance on familiarity obtained whether the stimuli were abstract laboratory stimuli or stimuli from the real threat categories of knives, guns and scissors."
This same reliance was observed under field conditions by British aviation security. While the same test images repeated from time to time, screeners' detection performance steadily improved. When the test images were replaced, however, screeners' performance dropped sharply, as though the improvement in performance was attributable to familiarity with specific tokens.
"Our desire to ground this field observation experimentally," Smith says, "was the primary motivation for our research. Our results complete a successful cycle of generalization from the real world to the laboratory, and they make a general statement across stimulus domains about constraints on humans' categorization abilities when they face visual complexity."
The reliance on familiarity might also have implications for the training and evaluation of screeners in the field for the following reason: The "Threat Image Projection" (TIP) system provides an important potential means of assessing performance at security checkpoints. It includes a library of test images that can be digitally injected into the X-ray image of a bag as it is presented to the screener. This lets screeners' ongoing target-detection performance be evaluated, provides ongoing training and maintains screener vigilance. Yet, a strategy of using a fixed library of test images risks the specific-token effects that Smith and his colleagues observed. Estimates of screener performance might be inflated by these familiarity effects, compared to the detection levels that would be observed for real threats that will be from outside the library and unfamiliar. A more conservative and truer estimate of screener performance would result if one arranged testing so that targets essentially never repeated, so that familiarity could never develop and so that screeners were forced to rely on category general knowledge and strategies.
Smith notes that it is to the Transportation Security Administration's credit that it has actively responded to this specific-token effect by increasing the size of TIP libraries and by planning periodically to infuse new targets. These changes have the potential to keep TIP as a viable and accurate indicator of detection levels in the security system. These steps also show the promise of cognitive scientists and sponsoring agencies cooperating toward solving important problems.