Characteristic views and the visual inspection of simple faceted and smooth objects: 'tetrahedra and potatoes'

The way in which human subjects distribute their time when attempting to learn the surface appearance of objects placed on a stand free to rotate about its vertical axis was investigated. Experiments were undertaken to establish whether observers concentrate their time on particular views and, if so, to determine the image characteristics of the preferred views. For tetrahedra, subjects concentrated on views which presented a face or an edge centred on the line of sight. Both of these views were symmetric about the vertical axis. For potatoes as examples of opaque smooth objects, subjects concentrated on four views in which the object's principal (long) axis was oriented side-on or end-on to their line of sight. For such views the horizontal width (and surface area) of the object's image had maximum and minimum values. Preferred views were not systematically related to views defined as stable from the appearance of surface boundaries or 'singularities'.