The use of optimal object information in fronto-parallel orientation discrimination

When determining an object's orientation an implicit object axis is formed, based on local contour information. Due to the oblique effect (i.e., the more precise perception of horizontal/vertical orientations than oblique orientations), an object's orientation will be perceived more precise if the axis is either horizontal or vertical than when the axis is oblique. In this study we investigated which object axis is used to determine orientation for objects containing multiple axes. We tested human subjects in a series of experiments using the method of adjustment. We found that observers always use object axes allowing for the highest object orientation discrimination, namely the axes lying closest to the horizontal/vertical. This implies that the weight the visual system attaches to axial object information is in accordance with the precision with which this information is perceived.