Perceptual sampling of orthogonal straight line features

Summary Among mathematical models of visual confusion of letters and similar material, those that posit a feature detection process have been especially popular. The present study 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 positioned 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 perceptibility (d) of a specific feature depended on the stimulus that contained it in the Gap condition but not in the Connected condition. The relative perceptibility 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.We would like to thank J.T. Berning for help in conducting the experiments. The first and second authors were supported by NSF Grant #BNS 76-84053 and the third author by Purdue Research Foundation Grant #XR 0104 during the early portions of this research. The latter portions were aided by National Science Foundation Grant #BNS 79-20298 to the first author. The third author is now at Human Performance Center, Ohio State University, Columbus, Ohio 43210. Send for reprints to Dr. James T. Townsend, Department of Psychological Sciences, Purdue University, West Lafayette, Indiana 47907, USA