Knowledge Representation by Arthur B. Markman;

Author:Arthur B. Markman; [Markman, Arthur B.]
Language: eng
Format: epub
ISBN: 9781134802975
Publisher: Taylor & Francis (Unlimited)
Published: 2023-06-15T00:00:00+00:00

Causal Information in Visual Object Representations

The previous two sections focused primarily on visual representations used for object recognition. These representations make an assumption that is easy to miss: that the point of visual representation is to store information about what the world outside looks like. There must be explicit representations of properties like edges, boundaries, or relations between parts of objects. This assumption seems plausible enough, although it is not necessary. Gibson (1950, 1986) argued that enduring representations of the properties of images in the visual world are not needed. Instead, he argued that people perceive aspects of the world in terms of their affordances. On his view, the goal of perception is to provide functional information about objects in the world such as whether things can be grasped, picked up, or walked around. (I discuss Gibson’s views about perception further in chap. 10.)

Visual representations may involve determining properties beyond the sizes and shapes of objects or their parts. One interesting theory of this type was developed by Leyton (1992), who argued that the purpose of vision is to extract causal information from the environment. He argued that symmetry in the world is a sign of the absence of causality and that asymmetries in the world reflect past causal forces. A simple example of this causal view is shown in Figure 6.9. At the right is a square. A square is symmetric in a variety of ways: All the sides are the same length, and all the angles are equal. A rectangle, like the one just to the left of the square, has two sides that are longer than the other two. Leyton suggested that the visual system interprets the longer sides as having been expanded by some force. Similarly, a parallelogram has angles that are not equal. Leyton argued that these can be interpreted as coming from a rectangle that has been sheared. Finally, the tilted parallelogram at the far left in Figure 6.9 has angles that diverge from the vertical and horizontal planes that help define the visual field. Leyton argued that this tilted parallelogram is interpreted as having been rotated by a force. On this view of vision, visual representation is not meant for representing perceptual properties of the visual world but rather for representing causal forces in the world.

Fig. 6.9 Causal transformations of a rotated parallelogram derived from asymmetries like those discussed by Leyton (1992). Leyton presented a detailed grammar of the forces likely to have acted on objects to create shapes. For example, a protrusion in a circle, like that shown in Figure 6.10A, can be detected as a set of changes in the curvature of the object. This protrusion can be interpreted as an inner force that has pushed outward. In contrast, an indentation in a perimeter can be interpreted as a resistance from the outside. In Figure 6.10B, the indentation in the center is viewed as the product of a resisting force pushing inward. The protrusions on either side of the indentation show evidence of forces pushing outward on either side of the resistance.

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