The usefulness of the $100-million security system around the Port Authority's airports depends ultimately on human observers [" 'Serious' breach," News, Aug. 14]. Many studies have shown that the detection of a target depends on how often any targets appear. If an agent is watching for intruders, and nothing of interest has occurred in days, attention lapses.

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It would help if the airport produced occasional random targets, in this case an intruder. There is good scientific data from the field of signal detection that quantifies lapses in attention due to infrequent stimuli.

Frank J. Mandriota, Bayport