By monitoring subjects' eye movements during a visual search task, we examined the possibility that the mechanism responsible for guiding attention during visual search has no memory for which locations have already been examined. Subjects did reexamine some items during their search, but the pattern of revisitations did notfit the predictions of the memory less search model. In addition, a large proportion of the refixations were directed at the target, suggesting that the revisitations were due to subjects' remembering which items had not been adequately identified. We also examined the patterns of fixations and compared them with the predictions of a memoryless search model Subjects' fixation patterns showed an increasing hazard function, whereas the memoryless model predicts a flat function. Lastly, we found no evidence suggesting that fixations were guided by amnesic covert scans that scouted the environment for new items during fixations. Results do not support the claims of the memorvless search model, and instead suggest that visual search does have memory.

Research has demonstrated that oculomotor visual search is guided by memory for which items or locations within a display have already been inspected. In the study reported here, we used a gaze-contingent search paradigm to examine properties of this memory. Data revealed a memory buffer for search history of three to four items. This buffer was effected in part by a space-based trace attached to a location independently of whether the object that had been seen at that position remained visible, and was subject to interference from other stimuli seen in the course of a trial.

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Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Abstract (a) Objective: Participants performed a tracking task and system monitoring task while aided by diagnostic automation. The goal of the study was to examine operator compliance and reliance as affected by automation failures, and to clarify claims regarding independence of these two constructs. (b) Background: Background data revealed a trend towards non-independence of the compliance-reliance constructs. (c) Method: Thirty-two undergraduate students performed the simulation that presented the visual display and collected dependent measures. (d) Results: False alarm prone automation hurt overall performance more than miss-prone automation. False alarm prone automation also clearly affected both operator compliance and reliance, while miss-prone automation only appeared to affect operator reliance. (e) Conclusion: Compliance and reliance do not appear to be entirely independent of each other. (f) Application: False alarms appear to be more damaging to overall performance than misses, and designers must take the compliancereliance constructs into affect.

The ability to perform multiple tasks simultaneously has become increasingly important as technologies such as cell phones and portable music players have become more common. In the current study, we examined dual-task costs in older and younger adults using a simulated street crossing task constructed in an immersive virtual environment with an integrated treadmill so that participants could walk as they would in the real world. Participants were asked to cross simulated streets of varying difficulty while either undistracted, listening to music, or conversing on a cell phone. Older adults were more vulnerable to dual-task impairments than younger adults when the crossing task was difficult; dual-task costs were largely absent in the younger adult group. Performance costs in older adults were primarily reflected in timeout rates. When conversing on a cell phone older adults were less likely to complete their crossing compared to when listening to music or undistracted. Analysis of time spent next to the street prior to each crossing, where participants were presumably analyzing traffic patterns and making decisions regarding when to cross, revealed that older adults took longer than younger adults to initiate their crossing, and that this difference was exacerbated during cell phone conversation, suggesting impairments in cognitive planning processes. Our data suggest that multi-tasking costs may be particularly dangerous for older adults even during everyday activities such as crossing the street.

An experiment examined visual performance in a simulated luggage-screening task. Observers participated in five sessions of a task requiring them to search for knives hidden in x-ray images of cluttered bags. Sensitivity and response times improved reliably as a result of practice. Eye movement data revealed that sensitivity increases were produced entirely by changes in observers' ability to recognize target objects, and not by changes in the effectiveness of visual scanning. Moreover, recognition skills were in part stimulus-specific, such that performance was degraded by the introduction of unfamiliar target objects. Implications for screener training are discussed.

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