Internal frame of reference as a determinant of the oblique effect

Theorists in perception have included peripheral or central factors in their explanations of the oblique effect. Studies investigating the central factors have shown that stimuli oriented vertically or horizontally have better encoding properties than do stimuli oriented obliquely and that oblique stimuli are more confusable. In the present study, the oblique effect was studied using single dots as stimuli. These dots were surrounded by either a square or a circle frame that provided information about their position in the visual field. The results of classification, focusing, and discrimination tasks showed that the processing of these dots followed the same pattern of results as it did with line stimuli: Dots located on the main axes (vertical and horizontal) were easier to classify than dots located on the oblique axes. The same pattern of results was found in both the square- and circle-frame experiments. The results suggest that an internal frame of reference, aligned with vertical and horizontal, facilitates processing of stimuli located on those axes.