Variant points of view on viewpoint invariance

In order to recognize an object, the visual system must make abstraction of proximal stimulus variations concomitant with the incidental vantage point. Theoretical models can be distinguished according to the degree to which they require the achievement of viewpoint independence prior to matching a stored object model. Recognition-by-components is one theory which incorporates the realization of general viewpoint invariance as one of its hallmarks. Some aspects of this theory, especially the orientation independence of the represented relations between object parts, are scrutinized. Next, an alternative approach is sketched in which object recognition is accomplished on the basis of a stimulus description which is dependent on the object's orientation, but which makes abstraction of other stimulus variations. Relevant neurophysiological findings are discussed, as well as behavioural evidence from experiments investigating orientation-dependent priming effects in the perception of biological motion.