By means of a variety of behavioral paradigms in humans and electrophysiological experiments in monkeys we have tried to demonstrate the existence of attention mechanisms allowing the selection of individual features (e.g. color, shape, etc.) of multi-dimensional visual stimuli. Various paradigms have been used for the experiments on human subjects, such as the “flanker task” and the “negative priming” paradigm. For the experiments on non-human primates we have recorded the firing activity of single neurons from the brain of animals actively engaged in performing a varietay of perceptual tasks.