Effect of line orientation on various information-processing tasks.

The effects of interstimulus and stimulus-specific factors on central (vs. peripheral) oblique effects were examined using classification, focusing, discrimination, and sequential same-different tasks. Classification results showed that grouping the vertical with the horizontal line and the two diagonal lines with each other facilitated performance. Discrimination results revealed that the two diagonal lines were more confusable with each other than were the members of any other stimulus pair. Focusing results indicated that the vertical and horizontal lines served as better focusing stimuli. A set of sequential same-different tasks, each using only two alternative stimuli, allowed for the examination of stimulus-specific factors in focusing; the effects of similarity relations between all stimuli in the total set were greatly reduced by the constrained context. The two diagonal lines were the most difficult to compare and proved to be the worst foci in these tasks as well. In conclusion, there are two factors operating in the central oblique effect: greater confusability between the two diagonal lines and more favorable stimulus-specific properties of vertical and horizontal lines.