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Two sets of studies examined the viability of using bat-like sonar input for artificial neural networks in complex pattern recognition tasks. In the first set of studies, a sonar neural network was required to perform two face recognition tasks. In the first task, the network was trained to recognize different faces regardless of facial expressions. Following training, the network was tested on its ability to generalize and correctly recognize faces using echoes of novel facial expressions that were not included in the training set. The neural network was able to recognize novel echoes of faces almost perfectly (above 96% accuracy) when it was required to recognize up to five faces. In the second face recognition task, a sonar neural network was trained to recognize the sex of 16 faces (eight males and eight females). After training, the network was able to correctly recognize novel echoes of those faces as 'male' or as 'female' faces with accuracy levels of 88%. However, the network was not able to recognize novel faces as 'male' or 'female' faces. In the second set of studies, a sonar neural network was required to learn to recognize the speed of a target that was moving towards the viewer. During training, the target was presented in a variety of orientations, and the network's performance was evaluated when the target was presented in novel orientations that were not included in the training set. The different orientations dramatically affected the amplitude and the frequency composition of the echoes. The neural network was able to learn and recognize the speed of a moving target, and to generalize to new orientations of the target. However, the network was not able to generalize to new speeds that were not included in the training set. The potential and limitations of using bat-like sonar as input for artifical neural networks are discussed.

The present study assessed consistency of recollections of personal circumstances of the 9/11 World Trade Center attack and events of the day before (9/10), and the day after (9/12), in a sample of 100 New York City college students. The day before 9/11 represented an ordinary event. A questionnaire was administered twice, 1 wk. and 1 yr. after the 9/11 attack. Students were asked to describe their personal circumstances when hearing about the news of the World Trade Center attack and for the same time of day for 9/10 and 9/12. 18 students returned the follow-up questionnaire. Consistency of initial and follow-up responses for the central categories for both 9/11 and 9/12 of where, who, and activity was very high (9/11: "Where"--100%, "Who"--100%, "What"--94%; 9/12: "Where"--100%, "Who"--100%, "What"--80%). Recollections of 9/10 were significantly less consistent ("Where"--79%, "Who"--71%, "What"--71%). Analysis indicated that students formed vivid, consistent recollections during the events of both 9/11 and 9/12. It is likely that the events of 9/12 also became flashbulb memories, vivid recollections of traumatic events, because the emotional impact of the stressful events, i.e., police and military presence, disrupted schedules, relating to the 9/11 attack endured beyond the day of the attack.

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