Human Systems Integration Division @ NASA Ames

We have investigated the perceived rigidity of rotating ellipses under a variety of conditions, following Wallach et al. (1956), who observed that rigidity is seen only when the eccentricity or aspect ratio is large. We measured the degree of rigidity as a function of aspect ratio, and found that a number of factors besides aspect ratio can have a profound effect of the percept. For example, a single rotating ellipse is often perceived to be more rigid than a family of concentric ellipses of the same aspect ratio. In a similar finding, we have observed that an asymmetric gaussian blob with elliptical contours is seen to be more rigid than a single ellipse, suggesting that low-frequency content may be important for rigidity. We have also considered the problem of how existing models of motion processing (the outputs of which are usually "flow fields") might be extended to generate categorical judgements of rigidity,and propose a model in which rigidity is seen when the deviation from the best fitting rigid interpretation is below some fixed criterion.