What is the term for the tendency to perceive the shape of an object as constant, even when its shape appears to change on the retina?

The concept being described is shape constancy, which refers to the perceptual phenomenon where an object is perceived as having the same shape, even when the angle or perspective changes, leading to alterations in its appearance on the retina. This ability allows us to recognize familiar objects despite changes in their visual presentation.

For instance, when viewing a door from different angles, it may appear to be a rectangle when viewed head-on but morphs into a trapezoid when seen from the side. Despite this visual change, we still understand that the shape of the door remains rectangular in its three-dimensional form. This perceptual skill is crucial for navigating and interacting with our environment, as it helps us maintain a consistent understanding of objects regardless of variations in perspective.

Other options, like form constancy, might seem similar but are more typically associated with the perception of shape in different contexts rather than the specific aspect of maintaining a consistent understanding of an object's shape. Figure-ground perception relates to our ability to distinguish an object from its background, and structural consistency isn’t a standard term used in psychological contexts. Thus, shape constancy is the most accurate term that defines the phenomenon described in the question.