Abstract
For most familiar objects, canonical view is a three-quarter view (i.e., oblique view between frontal view and profile view). Why does oblique orientation provide subjectively good, typical view of object? Here we propose a novel account for this. We conducted an object-orientation evaluation experiment. Pictures of familiar objects were presented, and participants evaluated the object orientations (i.e., azimuth angles) by rotating a disk so that its orientation matched to the orientation of presented object. Results showed that front, side and back orientations were evaluated accurately but oblique orientations were evaluated with significant errors (i.e., greater deviations from true orientations). Based on this data, we estimated the participants' sensitivity to object orientation, and found that they showed relatively low sensitivity to oblique orientations. This finding suggests that oblique orientations are only coarsely represented in the human visual system. To examine the relationship between object orientation perception and view-goodness, we conducted an analysis by objects. Based on the data mentioned above, we calculated orientations in which the orientation sensitivity is lowest (i.e., orientations which the participants can determine worst) for each of the stimulus objects. We also conducted a view-goodness rating experiment and estimated the orientations in which view-goodness is maximum for each object. Finally, we found that the least-sensitive orientations and maximum view-goodness orientations were significantly correlated, that is, views in which object orientation is poorly perceived are subjectively good views. Because oblique views contain more view-invariant features, they lack clues to determine object orientation precisely. Such characteristic would yield a consequence that views of various oblique orientations are visually similar to each other and perceived as single category of view, namely, a three-quarter view. This category includes broad range of object orientation, and then that view would be rated more familiar and typical.