Perceptual sampling of orthogonal straight line features.

Among mathematical models of visual confusion of letters and similar material, those that posit a feature detect ion process have been especially popular. The present s tudy provides direct tests of several of the central assumptions of such models with feature-stimuli composed of the blank, one of two straight line features, or both line. features posit ioned at a right angle. In one condition, the two features were connected when they appeared together, whereas in the other condition they were separated by a gap. A model which makes the strong assumptions that the features are sampled ( 'detected ' ) independently and then reported in a direct, unbiased fashion, performed acceptably in both conditions. Feature dependency models and those positing a biased decision process were ruled out on the basis of poor fits or lack of parsimony. The perceptibil i ty (d') of a specific feature depended on the stimulus that contained it in the Gap condit ion but not in the Connected condition. The relative perceptibil i ty of the horizontal vs in the vertical features was also different in the Gap vs Connected conditions. The results were compared with other recent studies, including ones in which sampling independence was falsified, apparently because of greater stimulus complexity, and employing a stimulus set that did not contain all possible combinations of features.