Processing line location and orientation.

For stimulus dimensions of line location and orientation with both card-sorting and discrete reaction-time trials, facilitation occurred when dimensions were positively correlated, and interference appeared when dimensions varied orthogonally. Interference could not be attributed to differential sensory accrual arising from positional uncertainty or to a repetition-effects advantage for control over orthogonal conditions. Facilitation tended to disappear when the same response was not required for the two dimensions, and when competing responses were required, interference appeared with redundant dimensions (negatively correlated stimulus sets). These data seem consistent with a model that calls for automatic and parallel extraction of features and their locations, with facilitation-interference effects having their locus in postperceptual response processing.