Visual perception of shape-transforming processes: 'Shape Scission'.

Shape-deforming processes (e.g., squashing, bending, twisting) can radically alter objects' shapes. After such a transformation, some features are due to the object's original form, while others are due to the transformation, yet it is challenging to separate the two. We tested whether observers can distinguish the causal origin of different features, teasing apart the characteristics of the original shape from those imposed by transformations, a process we call 'shape scission'. Using computer graphics, we created 8 unfamiliar objects and subjected each to 8 transformations (e.g., "twisted", "inflated", "melted"). One group of participants named transformations consistently. A second group arranged cards depicting the objects into classes according to either (i) the original shape or (ii) the type of transformation. They could do this almost perfectly, suggesting that they readily distinguish the causal origin of shape features. Another group used a digital painting interface to indicate which locations on the objects appeared transformed, with responses suggesting they can localise features caused by transformations. Finally, we parametrically varied the magnitude of the transformations, and asked another group to rate the degree of transformation. Ratings correlated strongly with transformation magnitude with a tendency to overestimate small magnitudes. Responses were predicted by both the magnitude and area affected by the transformation. Together, the findings suggest that observers can scission object shapes into original shape and transformation features and access the resulting representational layers at will.