The article by Jan Theeuwes investigates the perceptual selectivity for color and form in visual search tasks. Through three experiments, Theeuwes examines whether the preattentive parallel stage can selectively guide the attentive stage to a particular, known relevant target feature. The experiments involve subjects searching for a salient green circle surrounded by either unique form (green squares) or unique color (red circles) among other elements. The results show that complete top-down selectivity toward a particular feature is not possible, even after extended and consistent practice. Selectivity depends on the relative discriminability of the stimulus dimensions: the presence of an irrelevant item with a unique color interferes with parallel search for a unique form, and vice versa. This suggests that the preattentive process calculates differences in features within dimensions, resulting in a pattern of activations that are then automatically shifted to the location of the most salient feature, regardless of whether it is a target or a distractor. The findings support a model where the preattentive stage operates without capacity limitations and in parallel, followed by a serial attention stage that shifts to the location of the most salient feature.The article by Jan Theeuwes investigates the perceptual selectivity for color and form in visual search tasks. Through three experiments, Theeuwes examines whether the preattentive parallel stage can selectively guide the attentive stage to a particular, known relevant target feature. The experiments involve subjects searching for a salient green circle surrounded by either unique form (green squares) or unique color (red circles) among other elements. The results show that complete top-down selectivity toward a particular feature is not possible, even after extended and consistent practice. Selectivity depends on the relative discriminability of the stimulus dimensions: the presence of an irrelevant item with a unique color interferes with parallel search for a unique form, and vice versa. This suggests that the preattentive process calculates differences in features within dimensions, resulting in a pattern of activations that are then automatically shifted to the location of the most salient feature, regardless of whether it is a target or a distractor. The findings support a model where the preattentive stage operates without capacity limitations and in parallel, followed by a serial attention stage that shifts to the location of the most salient feature.