Mechanismen underlying visual search in barn owls.

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Visual search is a cognitive ability of humans and animals. During visual search attention is attracted to salient stimuli in the environment. In laboratory research observers are asked to search a target item in a scene containing many distracter items. In easy search tasks, search time and number of fixations do not depend on the number of other items presented. Therefore, such a search is also called parallel or feature search. The target is said to pop out. We have recently shown on the behavioral level that barn owls have a pop-out effect, similar to what is known from humans. Now we propose to study the neural basis of visual-search mechanisms in the barn owl and to further compare the behavior of barn owls with that of humans. Specifically we propose to record neural activity from awake, actively fixating owls while they are stimulated with visual-search patterns. We expect to find neurons in the forebrain of the barn owls that are sensitive to feature-search stimuli. The response of such neurons would differ in a situation when the target has the same orientation as the distracters and when it has a different orientation than the distracters. The same experiments will be done in sedated, passively viewing owls to see what difference an active behavior makes in the neural responses. Furthermore, we want to use stimulus paradigms recently tested in humans to see whether owls react to these stimuli similarly as humans do. All in all these experiments are intended to increase our knowledge about how evolution has shaped brains to cope with complex visual environments.