The article explores the preattentive parallel stage of visual processing and its ability to guide the subsequent serial attention. It discusses the findings of three visual-search experiments that tested whether the preattentive stage can selectively guide attention to a specific target feature. The results showed 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. The article outlines a model where the preattentive process computes differences in features within each stimulus dimension, resulting in an activation map. This process is followed by a stage involving focal attention that is directed serially to the location with the highest activity. Selectivity is determined by bottom-up activations caused by differences in features within different stimulus dimensions. The findings suggest that the preattentive process can only perform local-mismatch detection followed by a serial stage in which the most mismatching areas are selected for further analysis. The results indicate that the preattentive process is not sensitive to top-down processing, and that selectivity depends on the relative discriminability of the stimulus dimensions. The experiments showed that when searching for a unique feature, the presence of an irrelevant item with a unique feature in the other dimension interferes with search. The results also showed that the presence of a unique color or form in the irrelevant dimension can affect search performance. The findings suggest that the preattentive process is not capable of selective attention to the known-to-be-relevant target feature, and that selectivity depends on the relative discriminability of the stimulus dimensions. The experiments also showed that the preattentive process is not sensitive to top-down processing, and that selectivity depends on the relative discriminability of the stimulus dimensions. The results suggest that the preattentive process is not capable of selective attention to the known-to-be-relevant target feature, and that selectivity depends on the relative discriminability of the stimulus dimensions. The findings support the model that assumes that the preattentive process calculates differences in features within stimulus dimensions, resulting in an activation map, followed by an attentive stage that automatically shifts to the location of the feature that pops out first.The article explores the preattentive parallel stage of visual processing and its ability to guide the subsequent serial attention. It discusses the findings of three visual-search experiments that tested whether the preattentive stage can selectively guide attention to a specific target feature. The results showed 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. The article outlines a model where the preattentive process computes differences in features within each stimulus dimension, resulting in an activation map. This process is followed by a stage involving focal attention that is directed serially to the location with the highest activity. Selectivity is determined by bottom-up activations caused by differences in features within different stimulus dimensions. The findings suggest that the preattentive process can only perform local-mismatch detection followed by a serial stage in which the most mismatching areas are selected for further analysis. The results indicate that the preattentive process is not sensitive to top-down processing, and that selectivity depends on the relative discriminability of the stimulus dimensions. The experiments showed that when searching for a unique feature, the presence of an irrelevant item with a unique feature in the other dimension interferes with search. The results also showed that the presence of a unique color or form in the irrelevant dimension can affect search performance. The findings suggest that the preattentive process is not capable of selective attention to the known-to-be-relevant target feature, and that selectivity depends on the relative discriminability of the stimulus dimensions. The experiments also showed that the preattentive process is not sensitive to top-down processing, and that selectivity depends on the relative discriminability of the stimulus dimensions. The results suggest that the preattentive process is not capable of selective attention to the known-to-be-relevant target feature, and that selectivity depends on the relative discriminability of the stimulus dimensions. The findings support the model that assumes that the preattentive process calculates differences in features within stimulus dimensions, resulting in an activation map, followed by an attentive stage that automatically shifts to the location of the feature that pops out first.