Theories of visual pattern recognition frequently assume that processing begins with an analysis of the pattern into component parts, which are often assumed to be line segments of particular orientations, lengths, positions, and curvatures. The present experiments measured discriminability of these simple parts when presented either in isolation or within configural contexts that provided no formal information useful for the discrimination. Certain contexts either impaired or did not affect performance. Other contexts were found, however, which dramatically improved discriminability. Thus, two patterns which differed only in a single part could be discriminated from each other more quickly than could their distinguishing parts shown in isolation. Further experiments suggest that this "configural superiority" effect influences perceptual components of processing rather than memorial components. The mechanism underlying configural superiority appears to be the detection of novel and distinguishing features, such as corners and intersections, which emerge when parts are placed in close proximity to each other. The outlines of a model for preattentive feature discrimination are presented.